OPERATION
- A power voltage of 5 V is applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the engine-A/T-ECU (terminal No. 98).
- The power voltage is earthed to the engine-A/T-ECU (terminal No. 88) <Vehicle except for Australia, South africa and Hong kong> or (terminal No. 96) <Vehicle except for Australia, South africa and Hong kong> from the engine coolant temperature sensor (terminal No. 2).
FUNCTION
- The engine coolant temperature sensor converts the engine coolant temperature into a voltage signal, and inputs the voltage to the engine-A/T-ECU.
- In response to the signal, the engine-A/T-ECU controls the fuel infection amount and the fast idle speed when the engine is cold state.
- The engine coolant temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the engine coolant temperature rises. Therefore, the sensor output voltage varies with the engine coolant temperature, and becomes lower as the engine coolant temperature rises.
TROUBLE JUDGMENT
Check Condition
- 2 seconds later after the ignition switch has been in "ON" position or just after the engine has started up.
Judgment Criteria
- The sensor output voltage is 4.6 V or more (water temperature of below
-45°C or equivalent) for 4 seconds.
- The sensor output voltage is 4.6 V or more (water temperature of below
-45°C or equivalent) for 2 seconds. <Vehicle except for Hong kong>
- The sensor output voltage is 0.1 V or less (water temperature of above
140°C or equivalent) for 4 seconds. <Vehicle for Hong kong>
- The sensor output voltage is 0.1 V or less (water temperature of above
140°C or equivalent) for 2 seconds. <Vehicle except for Hong kong>
- The sensor output voltage rises 1.6 V or more (engine
coolant temperature below
40°C or equivalent) from 1.6 V or less (engine coolant temperature above40°C or equivalent).
PROBABLE CAUSE
- Failed engine coolant temperature sensor
- Open/short circuit in engine coolant temperature sensor circuit or loose connector contact
- Failed engine-A/T-ECU
STEP 1. MUT-II/III data list
- Item 21: Engine coolant temperature sensor
OK:
- Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
- Engine hot state: At 80 -
120°C
Q: Is the check result normal?
YES:
Intermittent malfunction (Refer to GROUP 00 -
How to Use Troubleshooting/Inspection
Service Points 
).NO: Go to Step 2
.)
Q: Is the check result normal?
YES:
Go to Step 3 .NO: Repair.
- Disconnect connector, and measure at sensor side.
- Resistance between terminal No. 1 and No. 2.
OK:
- Engine coolant temperature at
-20°C : 14 - 17 kΩ
- Engine coolant temperature at
0°C : 5.1 - 6.5 kΩ
- Engine coolant temperature at
20°C : 2.1 - 2.7 kΩ
- Engine coolant temperature at
40°C : 0.9 - 1.3 kΩ
- Engine coolant temperature at
60°C : 0.48 - 0.68 kΩ
- Engine coolant temperature at
80°C : 0.26 - 0.36 kΩ
Q: Is the check result normal?
YES:
Go to Step 4 .NO: Replace engine coolant temperature sensor.
- Disconnect connector and measure at harness side.
- Resistance between terminal No. 2 and earth.
OK: 2 Ω
or less
Q: Is the check result normal?
YES:
Go to Step 8 .NO: Go to Step 5
.)
YES:
Go to Step 6 .
NO: Repair.
.NO: Repair.
- Check earthing line for open circuit and damage.
Q: Is the check result normal?
YES:
Go to Step 7 .NO: Repair.
STEP 7. MUT-II/III data list
- Item 21: Engine coolant temperature sensor
OK:
- Engine cold state: At ambient temperature (atmospheric temperature) or equivalent.
- Engine hot state: At 80 -
120
°C
Q: Is the check result normal?
YES:
Intermittent malfunction (Refer to GROUP 00 -
How to Use Troubleshooting/Inspection
Service Points ).NO: Replace engine-A/T-ECU.
- Disconnect connector, and measure at harness side.
- Ignition switch: ON
- Voltage between terminal No. 1 and earth.
OK: 4.5 -
4.9 V
Q: Is the check result normal?
YES:
Go to Step 13 .NO: Go to Step 9
.
- Measure engine-A/T-ECU terminal voltage.
- Disconnect B-108 engine coolant temperature sensor.
- Ignition switch: ON
- Voltage between terminal No. 98 and earth.
OK: 4.5 -
4.9 V
Q: Is the check result normal?
YES:
Go to Step 10 .NO: Go to Step 11
.
Q: Is the check result normal?
YES:
- Check and repair harness between B-108 (terminal No. 1) engine coolant temperature sensor connector and C-137 (terminal No. 98) engine-A/T-ECU connector.
- Check output line for open circuit.
Q: Is the check result normal?
YES:
Go to Step 12 .NO: Repair.
- Check output line for short circuit.
Q: Is the check result normal?
YES:
Go to Step 7 .NO: Repair.
- Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
- Ignition switch: ON
- Voltage between terminal No. 1 and earth.
OK:
- Engine coolant temperature at
-20°C : 3.9 - 4.5 V
- Engine coolant temperature at
0°C : 3.2 - 3.8 V
- Engine coolant temperature at
20°C : 2.3 - 2.9 V
- Engine coolant temperature at
40°C : 1.3 - 1.9 V
- Engine coolant temperature at
60°C : 0.7 - 1.3 V
- Engine coolant temperature at
80°C : 0.3 - 0.9 V
Q: Is the check result normal?
YES:
Go to Step 7 .NO: Go to Step 14
.
Q: Is the check result normal?
YES:
Go to Step 15 .NO: Repair.
- Check output line for damage.
Q: Is the check result normal?
YES:
Go to Step 7 .NO: Repair.