DTC Troubleshooting

DTC Troubleshooting: P0128 (87-2)

DTC P0128:

Cooling System Malfunction

NOTE: Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information Initial Inspection and Diagnostic Overview.

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 the FAN LOW CTRL in the DATA LIST with the HDS.

Is it OFF?

YES -

Go to step 5.

NO -

Wait until the FAN HIGH CTRL and FAN LOW CTRL in the DATA LIST are off, then go to step 5.

5. Check the radiator fan operation.

Does the radiator fan keep running?

YES -

Check the radiator fan and A/C condenser fan circuit Radiator Fan and A/C Condenser Fan Circuit Troubleshooting. Also check the radiator fan relay Power Relay Test. If the circuit and the relay are OK, go to step 19.

NO -

Go to step 6.

6. Let the engine cool until the coolant temperature is 104 °F (40 °C) or less.

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

8. Start the engine, and let it idle.

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

10. Check ECT SENSOR 2 in the DATA LIST with the HDS.

11. Compare the value of recorded ECT SENSOR 2 and the present value of ECT SENSOR 2.

Did the temperature rise 14 °F (8 °C) or more?

YES -

Test the thermostat Service and Repair, then go to step 12.

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 PCM.�

12. Turn the ignition switch to ON (II).

13. Reset the PCM with the HDS.

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

15. Do the PCM idle learn procedure PCM Idle Learn Procedure.

16. Test-drive at a steady speed between 15-75 mph (24-120 km/h) for 10 minutes.

17. Check for Pending or Confirmed DTCs with the HDS.

Is DTC P0128 indicated?

YES -

Check the cooling system, then go to step 19.

NO -

Go to step 18.

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

Does the HDS indicate PASSED?

YES -

Troubleshooting is complete. If any other Pending or Confirmed DTCs were indicated in step 17, go to the indicated DTC's troubleshooting.�

NO -

If the HDS indicates FAILED, check the cooling system, then go to step 1. If the HDS indicates NOT COMPLETED, go to step 14.

19. Update the PCM if it does not have the latest software PCM Update, or substitute a known-good PCM.

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

21. Start the engine. Hold the engine speed at 3,000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

22. Test-drive at a steady speed between 15-75 mph (24-120 km/h) for 10 minutes.

23. Check for Pending or Confirmed DTCs with the HDS.

Is DTC P0128 indicated?

YES -

Check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the PCM. If the PCM was updated, substitute a known-good PCM, then go to step 20. If the PCM was substituted, go to step 1.

NO -

Go to step 24.

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

Does the HDS indicate PASSED?

YES -

If the PCM was updated, troubleshooting is complete. If the PCM was substituted, replace the original PCM Service and Repair. If any other Pending or Confirmed DTCs were indicated in step 23, go to the indicated DTC's troubleshooting.�

NO -

If the HDS indicates FAILED, check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the PCM. If the PCM was updated, substitute a known-good PCM, then go to step 20. If the PCM was substituted, go to step 1. If the HDS indicates NOT COMPLETED, go to step 20.