JPH11351976A - Trouble diagnosing apparatus for engine temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively detect a stack trouble of an engine temperature sensor or particularly a high stack trouble of a high temperature side. SOLUTION: At the time of executing at least once or more (preferably five to ten times) of the state that a vehicle speed is about 30 km/hr or more and the state that the speed is not the 30 km/hr or more after an engine is started, if a changing degree (a difference between a maximum value thwmax and a minimum value thwmin) of an output value of a water temperature sensor during a period so far is larger than a predetermined value, it is decided normal, and if not, it is decided abnormal. This process is executed when an atmospheric temperature is, for example, 35 deg.C or lower when started at a high temperature engine. Meanwhile, when started at a low temperature engine, the normal or the abnormal is decided according to whether the changing degree of the output value of the sensor is larger than the predetermined value or not during a period so far at the time of elapsing a predetermined time at the time of starting the engine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a failure diagnosis device for an engine temperature sensor such as a water temperature sensor for detecting the temperature of engine cooling water.

[0002]

2. Description of the Related Art Failures of a temperature sensor such as a water temperature sensor for detecting the temperature of engine cooling water include a short-circuit, a disconnection failure, and a stack failure in which a sensor output is fixed at a constant value. As means for determining a stack failure of the temperature sensor, for example, as described in Japanese Patent Publication No. 3-56417, a sensor output after a predetermined time has elapsed since the engine was started is compared with a predetermined determination value. It is known that when the output sticks to one side with respect to the determination value, it is determined that the temperature sensor is abnormal.

[0003]

By the way, the stack failure of the temperature sensor includes, for example, a low stack in which the sensor output is fixed at a low temperature (low) side of, for example, 20 ° C. or less, and a 20 ° C.
There is a high stack that sticks on the high temperature side (high) exceeding
The failure determination can be performed by the conventional failure determination means that determines that the temperature sensor is abnormal when the output value after a predetermined time has elapsed from the start of the engine and sticks to one side of the determination value. For example, when the present invention is applied to a water temperature sensor, if the sensor output does not increase from, for example, 10 ° C. even after a lapse of a predetermined time from the start of the engine, it can be determined that the low-side stack is present. However, in the case of the high stack in which the sensor output is stuck on the high temperature side exceeding, for example, 20 ° C., the stack failure cannot always be reliably determined by the conventional failure determination means.

As described above, the high stack is a failure in which the sensor output is stuck on the high temperature side exceeding, for example, 20.degree. C., but when the engine is stopped and restarted in a short time, the water temperature becomes 70.degree. At the time of a warm start that changes at a high temperature such as ° C., it is difficult to distinguish between normal and abnormal when the sensor output is fixed at a temperature close to the water temperature at the time of the warm start.

Therefore, it is an object to reliably determine a stack failure of an engine temperature sensor such as a water temperature sensor, particularly a high stack failure on a high temperature side.

[0006]

An engine temperature sensor failure diagnostic apparatus according to the present invention diagnoses a failure of a temperature sensor for detecting an engine temperature based on a change state of an output value of the temperature sensor. Load state determining means for determining whether the load is in a predetermined state; and, after starting the engine, the load state determining means determines at least once that the engine load is in the predetermined state and that the engine load is not in the predetermined state. Waiting for the above-described execution, comparing the degree of change in the output value of the temperature sensor in the period up to that time with a predetermined degree, and when the degree of change in the output value is within the predetermined degree, the temperature sensor is abnormal. Is provided.

[0007] The engine temperature depends on the calorific value of the engine, and the calorific value is substantially proportional to the intake air amount of the engine, that is, the load. Therefore, if the load of the engine changes, the engine temperature changes, and unless there is a failure in the temperature sensor, the sensor output changes according to the change in the load. For example, in the case of an engine that drives a vehicle, the degree of change in the output value of the temperature sensor during a period in which the engine load is in a predetermined state and not in a predetermined state at least once from a normal driving mode. Therefore, there is such a specific load state (predetermined state) such that a high stack failure in which the sensor output is stuck on the high temperature side can be reliably determined. Then, after the engine is started, when the load of the engine is in such a predetermined state and when it is not at least once, if the change in the output value of the temperature sensor in the period up to that time is within the predetermined degree, it is determined that the temperature sensor is abnormal. It can be determined.

In the above failure diagnosis apparatus, it is preferable that the abnormality determination means performs the determination when the engine temperature at the time of starting the engine is equal to or higher than a predetermined temperature. In this case, by setting the predetermined temperature near the engine temperature at the time of high temperature restart, that is, at the time of warm start, even at the time of the warm start at which the engine temperature changes at a high temperature, at the temperature close to the water temperature at the time of the warm start. The high stack on the high temperature side to which the sensor output is fixed can be reliably determined.

Preferably, the abnormality determining means performs the determination when the outside air temperature at the time of starting the engine is equal to or lower than a predetermined temperature. The predetermined temperature is, for example, 35 ° C. If the engine is restarted when the outside air temperature is higher than 35 ° C., for example, the engine water temperature will be 100 ° C. regardless of the load condition.
To the high temperature side close to
Cannot determine stack. Therefore, the determination is performed when the outside air temperature at the time of starting the engine is equal to or lower than the predetermined temperature.

In a normal running mode of a vehicle, a high stack fault is detected based on the degree of change in the output value of the temperature sensor during a period in which the engine load is in a predetermined state and is not in a predetermined state at least once. There is such a load state (predetermined state) that can be reliably determined. After the engine starts, when the engine load has passed at least once during the predetermined state and when the engine load has not been the same, the temperature during the period up to that time If the degree of change in the output value of the sensor is within a predetermined degree, it is possible to determine that the temperature sensor is abnormal, as described above. In this case, the predetermined state is, for example, when the intake air amount of the engine is equal to or more than a predetermined value. This is a predetermined load range equal to or more than the medium load.

In a normal driving mode, the operation is not frequently switched between a low load and a load region having a middle load or more, and the switching between the load regions is performed for a time period in which a change in the engine temperature appears. It is usually executed in Further, when switching between regions where the amount of intake air is small, a change in temperature is unlikely to appear because the amount of heat generation is small even as an absolute amount. Therefore, the accuracy of the abnormality determination of the temperature sensor can be improved by setting the predetermined state to a predetermined load region that is equal to or higher than a medium load where the intake air amount of the engine is equal to or higher than a predetermined value. Then, the predetermined load range, that is, the predetermined load range above the medium load where the intake air amount of the engine is equal to or more than the predetermined value, that is, the predetermined state may be determined by the vehicle speed in the case of the engine that drives the vehicle. That is, when the speed of the vehicle driven by the engine is equal to or higher than the predetermined speed, the predetermined state is determined. After the engine is started, the vehicle speed is equal to or higher than the predetermined speed and at least once when the vehicle speed is not higher. If the degree of change in the output value of the temperature sensor during the period up to that time is within a predetermined degree, the temperature sensor can be determined to be abnormal. The predetermined speed is, for example, 30 km / h. The vehicle speed of, for example, 30 km / h or more generally corresponds to a load region of a medium load or more where the intake air amount of the engine becomes a predetermined value or more.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows the entire structure of an automobile engine provided with a failure diagnosis apparatus to which the present invention is applied.

In FIG. 1, 1 is an engine body, and 2 is a combustion chamber thereof. An intake port 3 and an exhaust port 4 are opened in the combustion chamber 2, and an intake valve 5 and an exhaust valve 6 are arranged at openings of the intake port 3 and the exhaust port 4 to the combustion chamber 2. An intake passage 7 is connected to an inlet of the intake port 3, and an exhaust passage 8 is connected to an outlet of the exhaust port 4. In the intake passage 7, an air cleaner 9, an air flow sensor 10, a throttle valve 11, a surge tank 12, and a fuel injection valve 1 are arranged in this order from the upstream side.
3 is provided, and a bypass passage 14 for bypassing the throttle valve 11 is provided. A bypass valve (ISC valve) 15 for controlling the idle speed is provided in the middle of the passage 14. A crank angle sensor 16 for detecting a crank angle signal is provided at a predetermined position of the engine body 1, and a water temperature sensor 17 for detecting the temperature of the engine cooling water is provided. A catalyst device 18 for purifying exhaust gas is provided in the middle of the exhaust passage 8, and an oxygen sensor 19 is provided upstream thereof.

An ignition plug 20 is provided at the top of the combustion chamber 2. In addition, EC which controls the engine in the car
U (engine control unit) 21 is provided, a warning light 22 is provided, and the vehicle speed sensor 2
3 are installed.

FIG. 2 shows a cooling system of the engine. This engine is, for example, an in-line four-cylinder gasoline engine, and a water jacket 30 for circulating cooling water through a cylinder block and a cylinder head is formed in the engine body 1. Cooling water is pressure-fed from left to right in the figure by a water pump 31 driven by a crankshaft (not shown) via a belt or the like, and the cooling water flows from the engine body 1 while flowing through the water jacket 30. Heated by heat, while the water temperature is lower than the set temperature of the thermostat valve 32, the thermostat valve 32 closes to circulate the cooling water from the water jacket 30 through the bypass passage 33,
On the other hand, when the cooling water temperature becomes higher than the set temperature, the thermostat valve 32 is opened, and the cooling water flows through the thermostat valve 32 into the upper hose 34 to reach the radiator 35,
Cooled while passing through the radiator 35, the lower hose 36
A cooling system is configured to flow through the inside and return to the water pump 31. The water temperature sensor 17 is provided at a position facing the water jacket 30. In the figure,
Reference numeral 37 denotes an electric fan for forcibly cooling the radiator 35 by sucking air from a front grill (not shown) when the cooling water temperature becomes higher than a predetermined value.
Is a heater core for heating the interior of the vehicle. The heater core 38
An upstream cooling water passage 39 and a downstream cooling water passage 40 are provided so that hot water circulates from the water jacket 30 on the engine side.
Is connected to the water jacket 30. The hot water flow rate is adjusted by a hot water valve (not shown) provided in the upstream cooling water passage 39.

The detection signals of the air flow sensor 10, the crank angle sensor 16, the water temperature sensor 17, the oxygen sensor 19, and the vehicle speed sensor 23 are input to the ECU 21 as control information. Then, based on the control information, the EC
In U21, processing of ignition timing control, processing of fuel injection control, I
Processing such as SC control is performed, and processing for failure diagnosis of the water temperature sensor 17 is performed.

The fault diagnosis process is for detecting a high stack fault which is fixed on the high temperature side where the output value of the water temperature sensor 17 exceeds 20 ° C. After the engine is started, the load of the engine is reduced. A change in the output value of the water temperature sensor 17 during at least one time between a state where the engine intake air amount is equal to or more than a predetermined value in a predetermined load region above a medium load (a predetermined state) and a state where it is not, at least once. If the degree is within the predetermined degree, it is determined that the water temperature sensor 17 is abnormal (high stack failure on the high temperature side). And
Specifically, the state of the load of the engine is viewed at the vehicle speed, and when the vehicle speed is 30 km / h or more, the predetermined state is considered.
Changes in the output value of the water temperature sensor 17 during at least one or more (preferably 5 to 10) times when the vehicle speed is 30 km / h or more and the vehicle speed is less than 30 km / h after the engine is started. Watch the degree. And
The output value thw of the water temperature sensor 17 during the above period changes, for example, as shown by a solid line in FIG.
If the difference between the maximum value thwmax and the minimum value thwmin of hw is larger than a predetermined value, it is determined that the hw is normal, and if it is not more than the predetermined value, it is determined that the hw is abnormal (high stack failure on the high temperature side).

However, after the engine is started, the vehicle speed is 30 km /
Since the above-described failure diagnosis processing for determining normal / abnormal based on the degree of change of the sensor output value during a period of at least one time of a state of h or more and a state of less than h is applied only to the determination of a high stack on the high temperature side. Therefore, the water temperature (sensor output) at the time of starting the engine becomes a predetermined temperature (for example, 70 ° C.).
The above processing is executed at the time of a warm start of at least (° C.). In this process, the outside air temperature is high and the water temperature at the time of restart is 100 ° C.
Since an erroneous determination occurs in a state of sticking near, when the outside air temperature at the time of starting is higher than a predetermined temperature (for example, 35 ° C.), it is not executed. On the other hand, at the time of a cold start in which the water temperature at the time of engine start is lower than the above-mentioned predetermined value, the system simply waits for a lapse of a predetermined time from the start of the engine, and changes the output value of the water temperature sensor 17 (the maximum value th
Normal / abnormal (high-temperature-side high-stack failure) is determined based on whether the difference between wmax and the minimum value thwmin) is greater than a predetermined value.

The specific procedure of the failure diagnosis processing is as shown in the flow charts of FIGS. 4 and 5, and is started after the start, and various information is input in step S101. And
In step S102, the current water temperature (sensor output value) th
Whether the current value thw is higher than the maximum value thwmax up to that point is checked, and if the current value thw is higher than the maximum value thwmax, the maximum value thwmax is updated in step S103, and the process proceeds to the next step S104, where the current value thw becomes the maximum value thwmax. th
If wmax or less, skip step S103 and proceed to step S104. Then, in skip S104, it is determined whether the current water temperature (sensor output value) thw is lower than the previous minimum value thwmin. If the current value thw is lower than the minimum value thwmin, the minimum value thwmin is updated in step S105. Proceeding to the next step S106, if the current value thw is equal to or greater than the minimum value thwmin, skip step S105 and proceed to step S106.

In step S106, it is checked whether or not the starting water temperature (sensor output value) ths is equal to or lower than a predetermined temperature thso (for example, 70 ° C.). If the starting water temperature ths is lower than the predetermined temperature thso (at a cold start), the process proceeds to S107, where the timer value T is added, and then the step S108 is performed.
It is determined whether the timer value T has reached a predetermined value To (for example, 300 seconds). If the timer value T has not reached the predetermined time To, the process returns to step S101 and returns to steps S101 to S108.
Is repeated, and when the predetermined value To is reached, step S1
Go to 09. Then, in step S109, it is determined whether the difference between the maximum value thwmax and the minimum value thwmin of the sensor output value is larger than a predetermined value K ₁ (for example, 2 ° C.), and the difference between the maximum value thwmax and the minimum value thwmin is determined to be a predetermined value. K ₁ is greater than time, and stores it in determined to be normal in step S110, when the predetermined value K ₁ or less, and stores it to the determination in step S111 abnormal (high-temperature side of the high-stack fault) At the same time, the warning light 22 is turned on.

On the other hand, at step 106, the starting water temperature ths
Is equal to or higher than the predetermined temperature thso (during warm start), the process proceeds to step S112, and it is determined whether or not the start-time outside air temperature has is equal to or lower than the predetermined temperature thasso (for example, 35 ° C.).
If the start-time outside air temperature has is not lower than the predetermined temperature isso, the process is terminated without any processing. If the start-time outside air temperature is is lower than the predetermined temperature isso, the process proceeds to step S113. In step S113, it is determined whether the vehicle speed V is equal to or higher than the predetermined vehicle speed Vo (for example, 30 km / h). If the vehicle speed V is not equal to or higher than the predetermined vehicle speed Vo, a flag F is set in step S114 (F = 1). Then, the process proceeds to step S118 described below. If the vehicle speed V is equal to or higher than the predetermined vehicle speed Vo in step S113, it is determined in step S115 whether F = 1. If F = 1, the predetermined vehicle speed Vo is shifted from a region not higher than the predetermined vehicle speed Vo.
The fact that the process has shifted to the above-mentioned area this time means that step S1
In step S11, the counter value C is added.
At step 7, the flag F is lowered (F = 0), and the process proceeds to step S118. If F = 1 is not satisfied in step S115, it means that the vehicle speed is equal to or higher than the predetermined vehicle speed Vo before the previous time, so that step S116 is skipped and step S117 is performed.
The flag F is lowered, and the process proceeds to step S118. And
In step S118, the counter value C becomes a predetermined value (for example, 1
0), and if it has not reached the predetermined value, the flow returns to step S101 to return to steps S101 to S118.
repeat. When the counter value C reaches a predetermined value, the maximum value thwm of the sensor output value is determined in step S109.
ax and a minimum value thwmin are checked to see if they are larger than a predetermined value K ₁ (for example, 2 ° C.), and a maximum value thwmax is determined.
Minimum value when the difference between thwmin is larger than the predetermined value K ₁ stores it in determined to be normal in step S110, when the predetermined value K ₁ or less, abnormal in step S 111 (high-temperature side of the high-stack and (Failure) is determined and stored, and the warning lamp 22 is turned on.

In this example, the vehicle speed is 30 k at the time of a warm start.
When the vehicle speed has been at least once more than m / h and the vehicle speed is lower than 30 km / h, the high temperature side high stack failure is diagnosed by observing the degree of change in the output value of the water temperature sensor 17 in the period up to that time. At the time of a cold start, when a predetermined time has elapsed after the start, the degree of change in the output value of the water temperature sensor 17 in the period up to that time is also diagnosed as a high-stack fault on the high-temperature side. Thus, the high-stack fault on the high-temperature side can be reliably diagnosed irrespective of the level of the water temperature at the start. However, it is conceivable that the vehicle speed frequently fluctuates at around 30 km / h depending on the way of driving. When the vehicle speed fluctuates, the water temperature does not change.
If the stack determination is made under the condition setting that the number of times when the speed is not less than m / h and when it is not the same has reached a predetermined number,
There is a risk of misjudgment. Therefore, in order to prevent erroneous determination even in such a case, the failure diagnosis processing may be changed as follows.

As an example, steps S113 to S118 in the flowcharts shown in FIGS. 4 and 5 are changed as shown in FIG.

In this case, in step S112, the starting outside air temperature “thas” is increased to a predetermined temperature “thaso” (for example, 35 ° C.).
In the following cases, the process proceeds to step S213, where the vehicle speed V becomes the first speed.
The predetermined vehicle speed V ₁ or (V ₁ <Vo) to see if, when the vehicle speed V is not the first predetermined vehicle speed V ₁ or more, step S
In 214 lowered second flag F _2, then step S21
First flagged F ₁ at 5, the flow returns to step S101.

If the vehicle speed V is equal to or higher than the _first predetermined vehicle speed V ₁ in step S 213, F ₁ = 0 in step S 216.
(After V ≧ V ₁ , the differential value of V has never been negative.) If F ₁ = 0, step S
Proceeding to 215, if F ₁ = 0, V is set in step S217.
See if the derivative of is positive. When the differential value of V is negative, the vehicle speed exceeds the first predetermined vehicle speed V ₁ , for example, 3
That it is vertically per 0 km / h, the process proceeds to step S215, the sets a first flag F _1.

Further, when the differential value of V is called positive in step S217, that it is elevated without vertically after the vehicle speed exceeds a first predetermined vehicle speed V _1, step S
Advances to 218, the vehicle speed V is the second predetermined vehicle speed V ₂ or more (Vo
<V ₂ ) is checked. And step S
If the vehicle speed V is the second predetermined vehicle speed V ₂ than in 218, after the vehicle speed V reaches the first predetermined vehicle speed V ₁ or more, the vehicle speed V remains differential value of V is positive a second predetermined vehicle speed that it becomes V ₂ or more, in this case, the process proceeds to step S219,
If not, the process returns to step S101.

In step S219, it is checked whether F ₂ = 0. If F ₂ = 0, the vehicle speed V has become equal to or higher than the first predetermined vehicle speed V ₁ , and the vehicle speed V has now become equal to or higher than the second predetermined vehicle speed V _{2 while} the differential value of V remains positive. adds the counter value C in step S220, then the second flag F ₂ was lowered (F ₂ = 0) at step S221, the process proceeds to step S222. Also, in step S219, F ₂ =
If it is not 0, the second predetermined vehicle speed V ₂
Because of the above, steps S220 and S221 are skipped, and the process proceeds to step S222.

Then, in step S222, it is determined whether or not the counter value C has reached a predetermined value (for example, 10). If the counter value C has not reached the predetermined value, the process returns to step S101 to repeat steps S101 to S222. When the counter value C reaches a predetermined value, the process proceeds to step S109, where the maximum value thwmax and the minimum value thw of the sensor output value are set.
It is determined whether or not the difference from min is greater than a predetermined value K ₁ (for example, 2 ° C.), and the maximum value thwmax and the minimum value thwmi are determined.
When the difference between n is larger than the predetermined value K ₁ is step S1
10 is determined to be normal by storing it, when the predetermined value K ₁ or less, stores it determines in step S111 abnormal (high-temperature side of the high-stack fault), a warning lamp is turned on 22 .

Instead of setting a condition that the vehicle speed is 30 km / h or more and a condition that the vehicle speed is not 30 km / h, it is also possible to look at a load variation that leads to a change in water temperature based on the variation range of the vehicle speed. Therefore, the processing of the failure diagnosis may be changed as follows.

As an example, steps S113 to S118 in the flowcharts shown in FIGS. 4 and 5 are changed as shown in FIG.

In this case, in step S112, the outside air temperature during at startup is increased to a predetermined temperature, for example, 35 ° C.
In the following cases, the process proceeds to step S313 and the current vehicle speed V
Is higher than the previous maximum value Vmax,
If the current value V is higher than the maximum value Vmax, step S3
In step S315, the maximum value Vmax is updated, and the next step S315 is performed.
When the current value V is equal to or less than the maximum value Vmax, the process skips step S314 and proceeds to step S315. Then, whether or not the current vehicle speed V is lower than the previous minimum value Vmin is determined in skip S315, and if the current value V is lower than the minimum value Vmin, the minimum value V is determined in step S316.
min is updated and the process proceeds to the next step S317. If the current value V is equal to or greater than the minimum value Vmin, the process skips step S316 and proceeds to step S317.

Next, at step S317, the maximum vehicle speed V
It is checked whether the differential value of the difference between max and the minimum value Vmin has become 0 (zero). Then, the maximum value Vmax of the vehicle speed
Differential value of the difference between the minimum value Vmin is lower the flag F ₁ 0 Otherwise step S318 and, then, step S3
At 19, Vmax and Vmin are returned to 0 (zero), and the process returns to step S101.

Then, in step S317, the differential value of the difference between the maximum value Vmax and the minimum value Vmin of the vehicle speed is 0 (zero).
, It is checked in step S320 whether the difference between Vmax and Vmin is equal to or greater than a predetermined value ΔVo. And Vma
If the difference between x and Vmin is smaller than ΔVo, the process returns to step S101. If the difference between Vmax and Vmin is equal to or more than ΔVo, the process proceeds to step S321.

Then, when the flow advances to step S321, F ₁
If F ₁ = 0, it is determined that the fluctuation range of the current vehicle speed has become equal to or greater than a predetermined value.
At step S22, the counter value C is added.
3 flagged F ₁ in (F ₁ = _1), the process proceeds to step S324. If F ₁ = 0 is not satisfied in step S321, it means that the fluctuation range of the vehicle speed has become equal to or larger than the predetermined value before the previous time, and the process skips step S322 and proceeds to step S323.

In step S324, it is determined whether the counter value C has reached a predetermined value (for example, 10). If the counter value C has not reached the predetermined value, the process returns to step S101 and repeats steps S101 to S324. When the counter value C reaches the predetermined value, the process proceeds to step S109, and it is determined whether the difference between the maximum value thwmax and the minimum value thwmin of the sensor output value is larger than a predetermined value K ₁ (for example, 2 ° C.). when the difference between the value thwmax and minimum thwmin is larger than the predetermined value K ₁ stores it in determined to be normal in step S110, a predetermined value K ₁ following time,
In step S111, it is determined that there is an abnormality (high stack failure on the high-temperature side), the information is stored, and the warning lamp 22 is turned on.

In each of the above examples, the condition setting for the failure determination is performed based on the vehicle speed. However, similar condition settings may be performed based on the amount of intake air and other parameters instead of the vehicle speed.

[0038]

According to the present invention, a stack failure of an engine temperature sensor such as a water temperature sensor, particularly a high stack failure on a high temperature side can be reliably detected.

[Brief description of the drawings]

FIG. 1 is an overall structural diagram of an engine according to an embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a cooling system of the engine.

FIG. 3 is a time chart of processing of a failure diagnosis of a water temperature sensor.

FIG. 4 is a flowchart (part 1) for executing a failure diagnosis process for a water temperature sensor according to an example of the embodiment;

FIG. 5 is a flowchart (part 2) for executing a failure diagnosis process of the water temperature sensor.

FIG. 6 is a part of a flowchart for executing processing for failure diagnosis of a water temperature sensor according to another example.

FIG. 7 is a part of a flowchart for executing a failure diagnosis process of a water temperature sensor according to still another example.

[Explanation of symbols]

 1 Engine Body 17 Water Temperature Sensor 21 ECU (Engine Control Unit) 22 Warning Light 23 Vehicle Speed Sensor

Claims (6)

[Claims] An engine temperature sensor failure diagnosis device for diagnosing a failure of a temperature sensor for detecting an engine temperature based on a change state of an output value of the temperature sensor determines whether or not an engine load is in a predetermined state. Load state determining means, and after starting the engine, the load state determining means waits at least once for determining that the load of the engine is in the predetermined state and for determining that the engine load is not in the predetermined state. Comparing the degree of change of the output value of the temperature sensor with the predetermined degree during the period of time, and determining that the temperature sensor is abnormal when the degree of change of the output value is within the predetermined degree. A failure diagnosis device for an engine temperature sensor. 2. The failure diagnosis device for an engine temperature sensor according to claim 1, wherein said abnormality determination means performs the determination when the engine temperature at the time of starting the engine is equal to or higher than a predetermined temperature. 3. The failure diagnosis device for an engine temperature sensor according to claim 1, wherein the abnormality determination means performs the determination when an outside air temperature at the time of starting the engine is equal to or lower than a predetermined temperature. 4. The failure diagnosis device for an engine temperature sensor according to claim 1, wherein the predetermined state is a predetermined load range above a middle load where an intake air amount of the engine becomes a predetermined value or more. 5. The fault diagnosis device for an engine temperature sensor according to claim 4, wherein the predetermined load range is a load range in which the speed of a vehicle driven by the engine is equal to or higher than a predetermined speed. 6. A failure diagnosis device for an engine temperature sensor for diagnosing a failure of a temperature sensor for detecting an engine temperature based on a change state of an output value of the temperature sensor, wherein a speed of a vehicle driven by the engine is equal to or higher than a predetermined speed. Vehicle speed state determining means for determining whether or not the vehicle speed is higher than or equal to the predetermined speed, and a determination that the vehicle speed is not higher than the predetermined speed is performed at least once by the vehicle speed state determining means after the engine is started. And comparing the degree of change in the output value of the temperature sensor in the period up to that time with a predetermined degree, and determining that the temperature sensor is abnormal when the degree of change in the output value is within the predetermined degree. An apparatus for diagnosing a failure of an engine temperature sensor, comprising a determination unit.