DTC P0128: Cooling System Malfunction
- Turn the ignition switch to ON (II).
- Clear the DTC with the HDS.
- Make sure the blower switch is OFF.
- 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.
- Check the radiator fan operation.
Does the radiator fan keep running?
YES -Check the radiator fan circuit (see RADIATOR FAN SWITCH TEST ). If the circuit and the switch are OK, go to step 19.
NO -Go to step 6.
- Let the engine cool until the coolant temperature is 104°F (40°C) or less.
- Note the value of ECT SENSOR 1 and ECT SENSOR 2 in the DATA LIST with the HDS.
- Start the engine, and let it idle.
- Let the engine idle until ECT SENSOR 1 goes up 49°F (27°C) or more from the recorded temperature.
- Check ECT SENSOR 2 in the DATA LIST with the HDS.
- Compare the recorded value of ECT SENSOR 2 and its current value.
Did temperature rise 17°F (9.5°C) or more from the recorded temperature?
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.
NO -Test the thermostat (see THERMOSTAT TEST ), then go to step 12.
- Turn the ignition switch to ON (II).
- Reset the ECM with the HDS.
- Let the engine cool until the coolant temperature is between 21°F (-6°C) and 104°F (40°C).
- Do the ECM idle learn procedure (see ECM IDLE LEARN PROCEDURE ).
- Test-drive at a steady speed between 15-75 mph (24-120 km/h) for 10 minutes.
- Check for Temporary DTCs or DTCs with the HDS.
Is DTC P0128 indicated?
YES -Check the cooling system (see COOLING SYSTEM ), then go to step 1.
NO -Go to step 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 Temporary DTCs or DTCs were indicated in step 17, go to the indicated DTC's troubleshooting.
NO -If the screen indicates FAILED, check the cooling system (see COOLING SYSTEM ), then go to step 1. If the screen indicates NOT COMPLETED, go to step 14
- Update the ECM if it does not have the latest software (see ECM UPDATE ), or substitute a known-good ECM (see SUBSTITUTING THE ECM ).
- Let the engine cool until the coolant temperature is between 21°F (-6°C) and 104°F (40°C).
- Start the engine. Hold the engine speed at 3,000 RPM without load (in neutral) until the radiator fan comes on, then let it idle.
- Test-drive at a steady speed between 15-75 mph (24-120 km/h) for 10 minutes.
- 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. If the ECM was updated, substitute a known-good ECM (see SUBSTITUTING THE ECM ), then go to step 20. If the ECM was substituted, go to step 1.
NO -Go to step 24.
- Monitor the OBD STATUS for DTC P0128 in the DTCs MENU with the HDS.
Does the screen indicate PASSED?
YES -If the ECM was updated, troubleshooting is complete. If the ECM was substituted, replace the original ECM (see ECM REPLACEMENT ). If any other Temporary DTCs or 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 ECM. If the ECM was updated, substitute a known-good ECM (see SUBSTITUTING THE ECM ), then go to step 20. If the ECM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 20 and recheck.