DTC Troubleshooting

Control System DTCs

DTC Troubleshooting: P0128

DTC P0128 : Cooling System Malfunction

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information How To Troubleshoot The Fuel And Emissions Systems.

1. Radiator fan control command check:

Radiator fan control command check
-1. Turn the ignition switch to ON (II).

-2. Clear the DTC with the HDS.

-3. Turn the blower switch off.

-4. Check the FAN HIGH CTRL and FAN LOW CTRL in the DATA LIST with the HDS.

Are they OFF?
-YES- Go to step 2.
-NO- Wait until the FAN HIGH CTRL and FAN LOW CTRL are off, then go to step 4.

2. Radiator fan operation check:

Radiator fan operation check
-1. Check the radiator fan operation.

Does the radiator fan keep running?
-YES- Go to step 3.
-NO- Wait until the FAN HIGH CTRL and FAN LOW CTRL are off, then go to step 4.

3. Radiator fan circuit and radiator fan relay check:

Radiator fan circuit and radiator fan relay check
-1. Check the radiator fan circuit, and the radiator fan relay.

Is it OK?
-YES- Repair the radiator fan circuit, and the radiator fan relay, then do the repair verification.
-NO- Update the ECM/PCM ECM/PCM Update if it does not have the latest software, or substitute a known-good ECM/PCM Service and Repair, then do the repair verification.

4. Problem verification:

Problem verification
-1. Let the engine cool until the coolant temperature is 104 °F (40 °C) or less.

-2. Note the value of ECT SENSOR 1 and ECT SENSOR 2 in the DATA LIST with the HDS.

-3. Start the engine, and let it idle.

-4. Let the engine idle until ECT SENSOR 1 goes up 36 °F (20 °C) or more from the recorded temperature.

-5. Check ECT SENSOR 2 in the DATA LIST with the HDS.

-6. Compare the recorded value of ECT SENSOR 2 and the present value of ECT SENSOR 2.

Did temperature rise 9 °F (5 °C) or more?
-YES- Test the thermostat Thermostat Removal, Installation, and Test and replace it if needed, then do the repair verification.
-NO- Intermittent failure, the system is OK at this time. Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the ECM/PCM.

Repair verification (OBD STATUS check):

-1. Turn the ignition switch to ON (II).

-2. Reset the ECM/PCM with the HDS How To Troubleshoot The Fuel And Emissions Systems.

-3. Let the engine cool until the coolant temperature is between 21 °F (-6 °C) and 104 °F (40 °C).

-4. Do the ECM/PCM idle learn procedure. ECM/PCM Idle Learn Procedure

-5. Test-drive at a steady speed between 15-75 mph (25-120 km/h) for 30 minutes.

-6. Monitor the OBD STATUS for DTC P0128 in the DTCs MENU with the HDS.

Does the HDS indicate PASSED, FAILED, or NOT COMPLETED?
-PASSED- Troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM Service and Repair. If any other Pending or Confirmed DTCs are indicated, go to the indicated DTC's troubleshooting.
-FAILED- Go to step 1 and recheck. If the ECM/PCM was updated, substitute a known-good ECM/PCM Service and Repair, then check the OBD STATUS again.
-NOT COMPLETED- Meet the test condition, and check the OBD STATUS again.