P0115

P0115
ECT Engine Coolant Temperature - Malfunction
ECT Sensor signal implausible





Function
The ECT Sensor measures the engine temperature and changes it to a signal for the Engine Control Module (ECM).
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.
From ECM pin 74 the ECT Sensor receives + 5 V and from pin 34, the ECM is internally connected to Ground (GND).

Diagnostic conditions
During the diagnosis of the ECT Sensor, the ECM records the temperature change (as a resistance change) of the engine at a certain starting temperature change within a certain time interval, when the engine coolant temperature must increase.
During a malfunction of the ECT Sensor and the consequential storage of the Diagnostic Trouble Code (DTC) P0115, the ECM switches to a fixed value which corresponds to a cylinder head temperature of 140.3°C. With this the malfunction of the ECT sensor has minimal influence on the operation of the engine at operating temperature. It may, however, lead to starting problems and poor acceleration during the warm-up period.





Wiring Diagram.

NOTE: If DTC P0115 is displayed as "Not detected" and the fault counter is above 1, there is a repeated fault (intermittent connection).









Diagnostic procedure.
Connect scan tool and read engine temperature.
1. Connect scan tool with adapter cable.
2. Switch ignition on.
- If OK. Read Fault memory.
3. Read cylinder head temperature.
- When fixed value is 140,3°C - Proceed to measure resistance at ECT Sensor.

Read fault counter
1. Dial menu point "Fault Memory"
2. Read fault.
3. During fault display the fault counter and the erase counter are shown.
4. Observe display of fault counter while moving connectors and wires. Loose connections will increase the numbers on the counter.
5. Repair loose connection.
6. Erase memory.
7. End

Measuring resistance at ECT Sensor
1. Disconnect white connector at connector panel in the engine compartment.
2. Connect Ohm meter with test lead in direction of ECT Sensor (connector tags).
3. Resistance values:
- 0°C = 4.4 - 6.8 kohms
- 20°C = 1.4 - 3.6 kohms
- 40°C = 1 - 1,3 kohms
- 80°C =250 - 390 ohms
- 100°C = 160 - 210 ohms.

- If not OK.: Replace ECT Sensor
- If OK: Check final output of ECM

Check final output of ECM
1. At removed connector of ECT Sensor, connect Volt meter (plug-in connectors) in direction of ECM
2. Switch ignition on.
Display: approx. 5 V
- If OK: Replace ECT Sensor
- If not OK: Check resistance in electrical circuit.

Check resistance in the electrical circuit
1. Switch ignition off, disconnect ECM.
2. With test lead, connect Ohm meter between pin 74 and pin 34 at the ECM connector
3. Resistance for engine at operating temperature: approx. 90 ohms
- If OK: Replace ECM
- If not OK: Check for wire break.

Check for wire break
1. Switch ignition off.
2. Remove connectors at ECM and ECT Sensor.
3. With Ohm meter, check between ECM connector pin 34 and ECT Sensor connector pin 3.
4. With Ohm meter, check between ECM connector pin 74 and ECT Sensor connector pin 1.
- Display each time: < 5 ohms
- If OK.: End Test
- If not OK: Replace wiring harness.

Checking short circuit in wiring harness
1. Switch ignition off.
2. Remove ECM connector and ECT Sensor connector.
3. Connect Ohm meter to ECM connector pin 34 and pin 74.
- Display: Infinite resistance
- If not OK: Replace wiring harness