P0115
P0115
ECT Sensor signal implausible
P0117
ECT Engine Coolant Temperature - Malfunction
Function
The ECT sensor measures the engine temperature by means of a variable resistor. For the sensor, transistors of group NTC (negative temperature coefficient) are used, which means that the resistance is lowered when the engine coolant temperature increases. The change in resistance is recorded by the ECM which accordingly adjusts the amount of injected fuel and the ignition point during the warm-up phase of the engine.
The ECT sensor receives + 5 V from ECM pin 74, and the ECM is internally connected to ground from pin 34.
Diagnostic conditions
P0115
60 seconds after engine start-up, load interruption. A fault is recorded after a debounce time of 2 seconds if the measured engine temperature is lower than the calculated engine temperature minus approx. 4°C.
P0117
A fault is recorded after a debounce time of 2 seconds if an engine temperature of less than 45°C is measured.
Resistance values:
-10 °C = 8.0 - 11.0 kOhms
20 °C = 2.0 - 3.0 kOhms
80 °C = 260 - 390 ohms
In the event of a malfunction of the ECT sensor, the ECM switches to a fixed value which corresponds to a cylinder head temperature of 130.5°C. Failure of the ECT sensor therefore has only a minimal influence on the operation of the engine at operating temperature. It may, however, lead to starting problems and poor acceleration in the case of a cold start and during the warm-up period.
Wiring Diagram
NOTE: The displayed engine temperature value may be the substitute value. In the event of misfiring in the third cylinder, the ECT sensor warms up too slowly, and this may lead to a fault being recorded erroneously.
Diagnostic procedure
P0115
P0117
Check ECT (NTC II) Sensor.
1. Remove connector in the engine compartment.
2. Connect ohmmeter to ECT (NTC II) Sensor connector, pins 1 and 3.
- Specified value: 2 - 3 kOhms at 20°C
Check Output voltage of ECM
1. Remove connector for ECT (NTC II) Sensor in the engine compartment.
2. Connect voltmeter to ECM connector, pin 1 and 3.
3. Ignition on.
- Specific value: approx. 5 V.
Check wiring from ECM to ECT (NTC II) Sensor for continuity.
1. Remove connector in the engine compartment.
2. Remove ECM connector.
3. Connect ohmmeter to ECM connector, pin 34 and connector, pin 3 in the engine compartment.
- Specified value: 0 - 5 ohms.
4. Connect ohmmeter to ECM connector, pin 74 and connector, pin 1 in the engine compartment.
- Specified value: 0 - 5 ohms.
Check wiring between ECM and ECT (NTC II) Sensor for short circuit to ground.
1. Remove connector in the engine compartment.
2. Remove ECM connector.
3. Connect ohmmeter to ECM connector pin 74 and to ground.
- Specified value: infinite resistance
- If meter reads 0 - 5 ohms, check wiring harness for chafing and pinching damage.
Check wiring from ECM to ECT (NTC II) Sensor for short circuit to B+.
1. Remove connector in the engine compartment.
2. Connect voltmeter (plus) to connector in the engine compartment pin 3 and to ground (minus).
3. Switch ignition on.
- Specified value: 0 Volt
4. Connect voltmeter (plus) to connector in the engine compartment pin 1 and to ground (minus).
5. Switch ignition on.
- Specified value: 5 Volt
- If meter reads battery voltage in both cases, check wiring harness for chafing and pinching damage.