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Diagnostic Procedures

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  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Are any engine coolant temperature DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, go to next step.
  3. Connect a scan tool. Turn ON the ignition, with the engine OFF. Disconnect the ECT sensor. Does the scan tool indicate that the ECT sensor is at a temperature that is colder than -31°F (-35°C)? If yes, go to next step. If no, see DTC P0117: ECT SENSOR CIRCUIT - LOW VOLTAGE  .
  4. Using a jumper wire, jumper the terminals at the ECT sensor harness connector together. Does the scan tool indicate the ECT is at a temperature that is more than 302°F (150°C)? If yes, go to next step. If no, see DTC P0118: ECT SENSOR CIRCUIT - HIGH VOLTAGE  .
    5. NOTE: Allow time for the engine to warm up if the engine has not already reached the specified temperature. Seven minutes is the maximum amount of time the engine should take to reach this temperature from a cold start. Less time should be necessary if the engine is already warm.
  5. Reconnect the ECT sensor. Start and idle the engine. With the engine idling, observe the ECT sensor display on the Engine 1 Data List of the scan tool. Does the scan tool indicate that the engine coolant temperature has reached 140°F (60°C)? If yes, see DIAGNOSTIC AIDS  . If no, go to next step.
  6. Use a Digital Multimeter (DMM) in order to measure the resistance of the ECT sensor. See appropriate SENSOR OPERATING RANGE CHARTS article. Is the ECT resistance close to the value that is indicated in the Temperature Vs Resistance table? If yes, go to next step. If no, go to step  8 .
  7. For an engine cooling system condition, check for the following conditions:
    • Thermostat operation.
    • Coolant level.
    • Coolant to water ratio.
    • Cooling fan operation etc.

    After repairs, go to step  9 .

  8. Replace the ECT sensor. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After replacement, go to next step.
  9. Using the scan tool, clear the DTCs. Start engine and idle the engine at the normal operating temperature. Select DTC and the Specific DTC function. Enter the DTC number that was set. Operate the vehicle within the Conditions for Setting DTC until the scan tool indicates the diagnostic ran. Does the scan tool indicate the diagnostic passed? If yes, go to next step. If no, go to step  2 .
  10. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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