Volt

DTC P0128

The engine control module (ECM) monitors the temperature of the engine coolant for engine control and as enabling criteria for some diagnostics.The ECM monitors the amount of time to reach a predetermined temperature based on the Start up ECT sensor. The ECM uses this temperature to determine if the engine has warmed up to the thermostat regulating temperature. If the engine coolant temperature does not increase normally or does not reach the thermostat regulating temperature, diagnostics that use the ECT as enabling criteria, may not run when expected. If the engine coolant temperature fails to reach the thermostat regulating temperature, before a predetermined amount of time, the DTC sets.

The ECM detects that the amount of time it takes for the ECT sensor to reach target temperature has exceeded a calibrated time.

DTC P0128 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Hybrid Modes of Operation Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

1. Vehicle OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Loss of Coolant and Cooling System Draining and Filling .
2. Vehicle in Service Mode, observe the DTC information with a scan tool. DTC P00B7, P0597, P0598, P0599, or P2181 should not be set.

⇒	If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

3. Engine running for 15 min with the A/C OFF.

Note: Depending on ambient temperature, it may take up to 4 min for the temperatures to equalise.

4. Command the engine coolant thermostat heater to 0% with a scan tool. Increase the engine speed to wide open throttle. Observe the scan tool ECT Sensor parameter. The temperature should increase to greater than 75°C (167°F).

⇒	If less than the specified value, replace the E41 engine coolant thermostat heater.

5. Command the engine coolant thermostat heater to 100% with a scan tool. Increase the engine speed to wide open throttle. Observe the scan tool radiator coolant temperature sensor and the ECT Sensor parameters. The radiator coolant temperature sensor and the ECT Sensor parameters should be within 20°C (68°F).
6. Engine idling, observe the DTC information with a scan tool. DTC P0128 should not set.
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. Vehicle OFF, disconnect the harness connector at the B34 engine coolant temperature sensor.
2. Vehicle OFF, all systems OFF. It may take up to 2 minutes for all vehicle systems to power down.Test for less than 5 Ω between the low reference circuit terminal 2 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 engine control module.

3. Vehicle in Service Mode, 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 2 for a short to ground. If the circuit tests normal, replace the K20 engine control module.

Note: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

4. Install a 3A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the scan tool ECT Sensor parameter is greater than 130°C (266°F).

⇒	If less 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.

5. If all circuits test normal, test or replace the B34 engine coolant temperature sensor.

Static Test

1. Vehicle OFF, remove the engine coolant temperature sensor.

Note: A thermometer can be used to test the sensor off the vehicle.

2. Test the B34 engine coolant temperature sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the Temperature Versus Resistance table and verify that the resistance is within 5% of the specification.

⇒	If not within the specified range, replace the B34 engine coolant temperature sensor.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.