Code No. P0115: Engine Coolant Temperature Sensor System

OPERATION

A power voltage of 5 V is applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the engine-ECU (terminal No. 14).
The power voltage is earthed to the engine-ECU (terminal No. 29) 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-ECU.
In response to the signal, the engine-ECU controls the fuel injection 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 Criterion

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 0.1 V or less (water temperature of above 140°C or equivalent) for 4 seconds.

Check Condition

After the engine has started up.

Judgment Criterion

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 above 40°C or equivalent).

PROBABLE CAUSE

Failed engine coolant temperature sensor
Open/short circuit and damage in engine coolant temperature sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

Item No. 8: 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?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Go to Step 2 .

STEP 2. Connector check: A-108 engine coolant temperature sensor connector

Q. Is the check result normal?

Go to Step 3 .

Repair or replace the connector.

STEP 3. Perform resistance measurement at A-108 engine coolant temperature sensor connector.

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?

Go to Step 4 .

Replace the engine coolant temperature sensor.

STEP 4. Perform resistance measurement at A-108 engine coolant temperature sensor connector.

Disconnect connector and measure at harness side.
Voltage between terminal No. 2 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 8 .

Go to Step 5 .

STEP 5. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 6 .

Repair or replace the connector.

STEP 6. Check harness between A-108 (terminal No. 2) engine coolant temperature sensor connector and A-34 (terminal No. 29) engine-ECU connector.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

Go to Step 7 .

Repair the damaged harness wire.

STEP 7. M.U.T.-III data list

Item No. 8: 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?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Replace the engine-ECU then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

STEP 8. Perform voltage measurement at A-108 engine coolant temperature sensor connector.

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?

Go to Step 13 .

Go to Step 9 .

STEP 9. Perform voltage measurement at A-34 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Disconnect A-108 engine coolant temperature sensor connector.
Ignition switch: ON
Voltage between terminal No. 14 and earth.

OK: 4.5 - 4.9 V

Q. Is the check result normal?

Go to Step 10 .

Go to Step 11 .

STEP 10. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Check output line for open circuit.

Repair or replace the connector.

STEP 11. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 12 .

Repair or replace the connector.

STEP 12. Check harness between A-108 (terminal No. 1) engine coolant temperature sensor connector and A-34 (terminal No. 14) engine-ECU connector.

Check output line for short circuit.

Q. Is the check result normal?

Go to Step 7 .

Repair the damaged harness wire.

STEP 13. Perform voltage measurement at A-108 engine coolant temperature sensor connector.

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?

Go to Step 7 .

Go to Step 14 .

STEP 14. Connector check: A-34 engine-ECU connector

Q. Is the check result normal?

Go to Step 15 .

Repair or replace the connector.

STEP 15. Check harness between A-108 (terminal No. 1) engine coolant temperature sensor connector and A-34 (terminal No. 14) engine-ECU connector.

Check output line for damage.

Q. Is the check result normal?

Go to Step 7 .

Repair or replace the connector.