DTC P0128: Cooling System Malfunction

1. Turn the ignition switch to ON (II).
2. Clear the DTC with the HDS.
3. Make sure the blower switch is off.
4. Check the FAN CTRL in the DATA LIST with the HDS.

   Is it OFF? 

   YES  -Go to step 5.

   NO  -Wait until the FAN CTRL is off, then go to step 5.

5. Check the radiator fan operation.

   Does the radiator fan keep running? 

   YES  -Check the radiator fan circuit (see RADIATOR FAN HIGH SPEED CIRCUIT TROUBLESHOOTING ) and the radiator fan relay (see 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 122°F (50°C) or less.
7. Quickly 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 is 162 °F (72 °C).
10. Check ECT SENSOR 2 in the DATA LIST with the HDS.
11. Compare the recorded value of ECT SENSOR 2 and the present value of ECT SENSOR 2.

    Did temperature rise 48 °F (9 °C) or more? 

    YES  -Test the thermostat (see FAN MOTOR TEST ), 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 19 °F (-7 °C) and 122 °F (50 °C).
15. Do the PCM idle learn procedure (see 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  -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 screen 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 screen indicates FAILED, check the cooling system (see COMPONENT LOCATION INDEX ). If the cooling system is OK, go to step 19. If the screen indicates NOT COMPLETED, go to step  14.

19. Update the PCM if it does not have the latest software (see PCM UPDATE ), or substitute a known-good PCM (see SUBSTITUTING THE PCM ).
20. Let the engine cool until the coolant temperature is between 19 °F (-7 °C) and 122 °F (50 °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 (see SUBSTITUTING THE 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 screen indicate PASSED? 

YES  -If the PCM was updated, troubleshooting is complete. If the PCM was substituted, replace the original PCM (see PCM REPLACEMENT ). If any other Pending or Confirmed DTCs were indicated in step 23, go to the indicated DTC's troubleshooting.

NO  -If the screen 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 (see SUBSTITUTING THE PCM ), then go to step  20. If the PCM was substituted, go to step  1. If the screen indicates NOT COMPLETED, go to step  20.