P0128
DTC P0128 (LUJ)
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions 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
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 26°C (78.8°F) colder than the commanded engine coolant temperature while the IAT is between 10-65°C (50-149°F)
or
The ECM detects that the actual engine coolant temperature is 46°C (114.8°F) colder than the commanded engine coolant temperature while the IAT is between -7°C to +10°C (-19.4 to+50°F)
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 [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition OFF, inspect the cooling system surge tank for the proper coolant level. Refer to Loss of Coolant Loss of Coolant and Cooling System Draining and Filling Cooling System Draining and Filling.
2. Ignition ON, 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 Diagnostic Trouble Code (DTC) List - Vehicle.
3. Engine idling for 15 min with the A/C OFF.
Note: Depending on ambient temperature, it may take up to 4 min for the temperatures to equalize.
4. Command the Engine Coolant Thermostat Heater to 0% with a scan tool. Increase the engine speed to 3 000 RPM. Observe the scan tool ECT Sensor parameter. The temperature should increase to greater than 102°C (215°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 3 000 RPM. 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. You may also operate the vehicle within the conditions that you observed from the freeze frame/failure records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the B34 Engine Coolant Temperature Sensor.
2. Ignition OFF for 1 min, test for less than 5 ohms 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. 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 2 for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.
Caution:
If the fuse in the jumper wire opens, the signal circuit may have a short to a voltage or a short to ground and the sensor might be damaged.
4. Install a 3 A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the scan tool ECT Sensor parameter is warmer than 139°C (282.2°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.
Component Testing
Static Test
1. Ignition off, disconnect the harness connector at the B34 Engine Coolant Temperature Sensor.
Note: A thermometer can be used to test the sensor off 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 (ECT) Temperature Versus Resistance (ECT) 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.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Engine Coolant Temperature Sensor Replacement (Water Outlet) Engine Coolant Temperature Sensor Replacement (Water Outlet)Engine Coolant Temperature Sensor Replacement (Thermostat) Engine Coolant Temperature Sensor Replacement (Thermostat)Engine Coolant Temperature Sensor Replacement (Radiator) Engine Coolant Temperature Sensor Replacement (Radiator)
* Engine Coolant Thermostat Housing Removal Service and Repair
* Control Module References Control Module References for ECM replacement, programming and setup