Chevrolet Trax: DTC P0128

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0128

Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature

Circuit/System Description

NOTE: The engine coolant temperature sensor is referred to as B34A Engine Coolant Temperature Sensor 1 in schematics and other areas.

The engine control module (ECM) monitors the temperature of the engine coolant for engine control and enabling criteria for some diagnostics. The amount of air flow into an engine is proportional to the amount of heat an engine generates. The ECM monitors the amount of air flow into the engine to calculate engine coolant temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the thermostat regulating temperature. If the ECT 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 ECT fails to reach the thermostat regulating temperature, before a predetermined amount of air flow enters the engine, the DTC sets.

Conditions for Running the DTC

• DTCs P00B3, P00B6, P0101, P0102, P0103, P0111, P0112, P0113, P0116, P0117 or P0118 are not set.
• Average Airflow is greater than 11 g/s.
• Thermostat Heater duty commanded cycle 10%.
• Engine not run time 30 min
• Engine run time between 22 s and 30 min
• The DTC runs once per ignition key cycle.

Conditions for Setting the DTC

The ECM detects that the actual engine coolant temperature is 26ºC (78.8ºF) colder than the commanded engine coolant temperature while the IAT is between 10-65ºC (50-149ºF)

or

The ECM detects that the actual engine coolant temperature is 46ºC (114.8ºF) colder than the commanded engine coolant temperature while the IAT is between -7ºC to +10ºC (-19.4 to+50ºF)

Action Taken When the DTC Sets

DTC P0128 is a Type B DTC

Conditions for Clearing the DTC

DTC P0128 is a Type B DTC.

Reference Information

Schematic Reference

Engine Controls Schematics (Encore) , Engine Controls Schematics (Trax)

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - ENCORE WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - TRAX

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (LUV) , Powertrain Diagnostic Trouble Code (DTC) Type Definitions (2H0)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify the cooling system is filled to the correct coolant level. Refer to Loss of Coolant , and Cooling System Draining and Filling .

• If the coolant level is not correct

Repair as necessary

• If the coolant level is correct

2. Verify the DTC P00B7, P0116, P0117, P0118, P0597, P0598, or P0599 is not set.

• If a DTC is set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle

• If a DTC is not set

3. Engine running for 15 min with the A/C OFF, increase the engine speed to 3,000 RPM.
4. Verify the scan tool ECT Sensor parameter is greater than 79ºC (174ºF) when commanding the Engine Coolant Thermostat Heater to 0%.

• If less than 79ºC (174ºF)

Replace the E41 Engine Coolant Thermostat Heater.

• If greater than 79ºC (174ºF)

5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
6. Verify the DTC does not set.

• If the DTC sets

Refer to Step 1.

• If the DTC does not set

7. All OK.

Component Testing

1. Ignition OFF, disconnect the B34 Engine Coolant Temperature Sensor harness connector at the sensor.
2. Test for refer to Temperature Versus Resistance Temperature Versus Resistance between the signal circuit terminal 1 and the low reference terminal 2.

• If the temperature versus resistance are not within the specified ranges

Replace the B34 Engine Coolant Temperature Sensor.

• If the temperature versus resistance are within the specified ranges

3. Test for infinite resistance between each terminal and the sensor housing

• If less than infinite resistance

Replace the B34 Engine Coolant Temperature Sensor.

• If infinite resistance

4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Engine Coolant Temperature Sensor Replacement (Water Outlet) , Engine Coolant Temperature Sensor Replacement (Radiator)
• Engine Coolant Thermostat Housing Removal
• Control Module References for engine control module replacement, programming and setup.

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