P0115 – Engine Coolant Temperature Sensor System MMC Colt

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

2 seconds later after the ignition switch has been in “ON” position or just after the engine has started up.

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.

After the engine has started up.

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 CAUSES

Failed engine coolant temperature sensor

Open or shorted engine coolant temperature sensor circuit, harness damage, or connector damage

Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Item No. 8: Engine coolant temperature sensor

Q. Is the check result normal?

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

Q. Is the check result normal?

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.

Q. Is the check result normal?

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.

Q. Is the check result normal?

STEP 5. Connector check: A-08 engine-ECU connector

Q. Is the check result normal?

STEP 6. Check harness between A-108 (terminal No. 2) engine coolant temperature sensor connector and A-08 (terminal No. 29) engine-ECU connector.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

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

Item No. 8: Engine coolant temperature sensor

Q. Is the check result normal?

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.

Q. Is the check result normal?

STEP 9. Perform voltage measurement at A-08 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.