Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
DTC P0128: Cooling System Malfunction ('06-08 models)
- Turn the ignition switch ON (II).
- Clear the DTC with the HDS.
- Turn the blower switch 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 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.
- 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 40°F (22°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 the present value of ECT SENSOR 2.
Did the temperature rise 14°F (8°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 (see THERMOSTAT TEST ), then go to step 12.
- Turn the ignition switch ON (II).
- Reset the ECM/PCM 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/PCM idle learn procedure (see ECM/PCM 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, 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 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 14.
- Update the ECM/PCM if it does not have the latest software (see UPDATING THE ECM/PCM ), or substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ).
- 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 Park or 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/PCM. If the ECM/PCM was updated, substitute a known-good ECM/PCM (see SUBSTITUTING THE ECM/PCM ), then go to step 20. If the ECM/PCM 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/PCM was updated, troubleshooting is complete. If the ECM/PCM was substituted, replace the original ECM/PCM (see '06-08 MODELS ). If any other Temporary DTCs or DTCs were indicated in step 23, 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 (see SUBSTITUTING THE ECM/PCM ), then go to step 20. If the ECM/PCM was substituted, go to step 1. If the screen indicates NOT COMPLETED, go to step 20.
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.