Cruze

DTC P0128

The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 V to the engine coolant temperature (ECT) sensor signal circuit and an ground for the low reference circuit. The purpose of this diagnostic is to analyse the performance of the thermostat by comparing the measured engine coolant temperature (ECT) sensor to a modelled engine coolant temperature using information from the following inputs:

The ECM uses the start up ECT and the start up IAT to begin the diagnostic calculation. The air flow into the engine is accumulated, and vehicle speed, distance, engine load, and engine run time are also factored in to determine if the ECT does increase normally and then maintains that temperature within a calibrated range of the modelled ECT.

The ECM determines that the modelled engine coolant temperature has met the calibrated target of +92°C (+198°F) and the measured engine coolant temperature (ECT) sensor is less than +81°C (+178°F) for greater than 2 s.

DTC P0128 00 is a Type B DTC.

The following conditions can also set the DTC:

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Turn OFF the ignition.
2. Inspect the cooling system surge tank for the proper engine coolant level. Refer to Cooling System Leak Testing and Cooling System Draining and Filling .
3. If the ignition has been OFF for 8 h or greater, the intake air temperature, the ambient temperature, and the engine coolant temperature should be within +9°C (+16°F) of each other. Ignition ON, observe the scan tool IAT Sensor, Ambient Air Temperature, ECT Sensor parameters. Compare those scan tool sensor parameters to each other and also to the ambient temperature to determine if the ECT Sensor is skewed colder.
4. Engine running, observe the scan tool ECT Sensor parameter. The reading should be between -39 to +120°C (-38 to +248°F) depending on the current ambient temperature and the vehicle operating conditions.
5. Use the scan tool to verify the proper operation of the engine cooling system fan.

Note: A critical analysis of the operation of the thermostat is necessary to properly diagnose this DTC.

6. Verify the proper heat range and the operation of the thermostat. Refer to Thermostat Diagnosis : 2.0L Diesel LNP → 2.0L Diesel LLW → LDE, L2W, LXT, LXV, 2H0, and LUW .
7. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.

1. Inspect the B74 Manifold Absolute Pressure Sensor and the B66 Intake Air Temperature Sensor elements for contamination and debris.
2. Ignition OFF, disconnect the harness connector at the B34A Evaporator Temperature Sensor 1.
3. Ignition OFF for 90 s, test for less than 5 Ω between the low reference circuit terminal 2 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

4. Ignition ON, verify the scan tool ECT Sensor parameter is colder than -39°C (-38°F).

⇒	If warmer than the specified range, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.

5. Install a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool ECT Sensor parameter is greater than 128°C (262°F).

⇒	If colder than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.

6. If all circuits/connections test normal, replace the B34A Engine Coolant Temperature Sensor 1.

Static Test

Measure and record the resistance of the K20 Engine Control Module Sensor at various ambient temperatures, then compare those measurements to the Temperature Versus Resistance : IAT → ECT .

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.