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P0128 Engine Too Cold Too long

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Mopar1973Man

By Mopar1973Man

DTC P0128: ENGINE IS COLD TOO LONG

Monitor & Set Conditions

Engine Coolant Temperature (ECT) sensor voltage is monitored when the engine is running, engine coolant temperature is 20 to 130°F (-6 to 55°C) and no ECT or battery temperature DTCs are set. DTC will set if coolant temperature reading is less than 170°F (77°C) after the engine has been running for 10-32 minutes (depending on engine coolant temperature at engine start).

Possible Causes

  • Wiring Harness
  • ECT Sensor
  • ECT Sensor - Engine Hot
  • ECM

Testing

1. Turn ignition off. Disconnect ECT sensor harness connector. The ECT sensor is located at the front of the cylinder head, near the thermostat housing. Inspect ECT sensor harness connector for miswired, corroded, pushed out or damaged terminals. If terminals are not miswired, corroded, pushed out or damaged, go to next step. If terminals are miswired, corroded, pushed out or damaged, repair as necessary.

2. This test procedure will be invalid if the thermostat is stuck open. Turn ignition on. Measure engine temperature near ECT sensor using an external temperature measuring device. Ensure engine temperature is less than 124°F (50°C). Using DRBIII(R) scan tool, monitor ECT sensor reading. If both temperature readings are within 10 percent of each other, go to next step. If both temperature readings are not within 10 percent of each other, replace the ECT sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article.

3. Continue monitoring engine temperature near ECT sensor using an external temperature measuring device and using a scan tool, continue monitoring ECT sensor reading. Start engine and allow it to reach a temperature greater than 180°F (82°C). If both temperature readings are within 10 percent of each other, replace and program the ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. If both temperature readings are not within 10 percent of each other, replace the ECT sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. If engine temperature does not reach 180°F (82° C), diagnose cooling system malfunction.

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