DTC Troubleshooting
DTC P0128: Cooling System MalfunctionNOTE: Before you troubleshoot, record ail freeze data and any on-board snapshot, and review the general troubleshooting information.
1. Turn the ignition switch ON (II).
2. Clear the DTC with the HDS.
3. Turn the blower switch OFF.
4. Turn the A/C switch OFF.
5. Check the FAN CTRL in the DATA LIST with the HDS.
Is it OFF?
YES - Go to step 6.
NO - Wait until the FAN CTRL is off, then go to step 6.
6. Check the radiator fan operation.
Does the radiator fan keep running?
YES - Check the radiator fan high speed circuit, and the radiator fan relay. If the circuits and the relay are OK, go to step 20.
NO - Go to step 7.
7. Let the engine cool until the coolant temperature is 104 °F (40 °C) or less.
8. Note the value of ECT SENSOR 1 and ECT SENSOR 2 in the DATA LIST with the HDS.
9. Start the engine, and let it idle.
10. Let the engine idle until ECT SENSOR 1 goes up 49 °F (27 °C) or more from the recorded temperature.
11. Check ECT SENSOR 2 in the DATA LIST with the HDS.
12. Compare the value of recorded ECT SENSOR 2 and the value of present ECT SENSOR 2.
Did temperature rise 17 °F (9.5 °C) or more?
YES - 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.
NO - Test the thermostat, then go to step 13.
13. Turn the ignition switch ON (II).
14. Reset the ECM/PCM with the HDS.
15. Let the engine cool until the coolant temperature is between 21 °F( - 6 °C) and 104 °F (40 °C).
16. Do the ECM/PCM idle learn procedure.
17. Test-drive at a steady speed between 15 - 75 mph (24 - 120 km/h) for 10 minutes.
18. Check for Temporary DTCs or DTCs with the HDS.
Is DTC P0128 indicated?
YES - Check the cooling system, then go to step 1.
NO - Go to step 19.
19. 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 Temporary DTCs or DTCs were indicated in step 18, go to the indicated DTCs troubleshooting.
NO - If the screen indicates FAILED, check the cooling system, then go to step 1. If the screen indicates NOT COMPLETED, go to step 17.
20. Update the ECM/PCM if it does not have the latest software, or substitute a known-good ECM/PCM.
21. Let the engine cool until the coolant temperature is between 21 °F (-6 °C) and 104 °F (40 °C).
22. Start the engine. Hold the engine speed at 3,000 rpm without load (in Park or neutral) until the radiator fan comes on, then let it idle.
23. Test-drive at a steady speed between 15 - 75 mph (24 - 120 km/h) for 10 minutes.
24. Check for Temporary DTCs or 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 ECM/PCM. If the ECM/PCM was updated, substitute a known-good ECM/PCM, then go to step 23. If the ECM/PCM was substituted, go to step 1.
NO - Go to step 25
25. Monitor the OBD STATUS for DTC P0128 in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES - If the ECM/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM. If any other Temporary DTCs or DTCs were indicated in step 24, go to the indicated DTCs troubleshooting.
NO - If the screen indicates FAILED, check for poor connections or loose terminals at ECT sensor 1, ECT sensor 2, and the ECM/PCM. If the ECM/PCM was updated, substitute a known-good ECM/PCM, then go to step 23. If the ECM/PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 23.