Note. Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information (see GENERAL TROUBLESHOOTING INFORMATION ).
- 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»(ref-221327-S40690856972006022400000) ). 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»(ref-221326-S09424395132006022400000) ), 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»(ref-221342-S09897997502006022400000) ).
- 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»(ref-221326) ), 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»(ref-221326) ), 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»(ref-351945-S31385529132009122900000) ), or substitute a known-good ECM (see «SUBSTITUTING THE ECM»(ref-221338-S28616532062006022400000) ).
- 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»(ref-221338-S28616532062006022400000) ), 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»(ref-351945-S35124653042009122900000) ). 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»(ref-221338-S28616532062006022400000) ), 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.