For a complete wiring diagram Refer to Section 8W.Engine Coolant Temperature Sensor performance looks at the outputs of three temperature sensors and compares them under cold start conditions. Following a start to run delay time, the outputs of the ambient, engine coolant, and intake air temperature sensors will be compared. If the intake air and ambient air temperature sensors agree and the engine coolant temperature does not agree, the engine coolant temperature sensor is declared as irrational.When Monitored:The engine off time is greater than 480 minutes. Ambient Temperature if greater than 4 °C (38 °F).Set Condition:After a calibrated amount of cool down time the PCM compares the ECT Sensor, IAT Sensor, and the Ambient Air Temp Sensor values. If the ECT Sensor value is not within 10°C (50°F) of the other two temperature sensors. Two Trip Fault. Three good trips to turn off the MIL. ETC light will illuminate.Possible CausesEXCESSIVE RESISTANCE IN THE (K2) ECT SIGNAL CIRCUITEXCESSIVE RESISTANCE IN THE (K900) SENSOR GROUND CIRCUITECT SENSORPCMAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCStart the engine.Allow the engine to reach normal operating temperature.With a scan tool, select View DTCs.It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.Is the DTC Active or Pending at this time?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 2. ECT SENSOR VOLTAGE ABOVE 4.6 VOLTSTurn the ignition off.Disconnect the ECT Sensor harness connector.Ignition on, engine not running.With a scan tool, read the ECT voltage.Is the voltage above 4.6 volts?YesGo To 3NoGo To 43. ECT SENSOR

Connect a jumper wire between the (K2) ECT Signal circuit and the (K900) Sensor ground circuit in the ECT Sensor harness connector.With a scan tool, read the ECT voltage.Is the voltage below 1.0 volt with the jumper wire installed?YesReplace the ECT Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 4Remove the jumper wire before continuing. 4. EXCESSIVE RESISTANCE IN THE (K2) ECT SIGNAL CIRCUITTurn the ignition off.Disconnect the C2 PCM harness connector.Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 and #8815-1 to perform diagnosis.Using a voltmeter perform a voltage drop test. Backprobe the (K2) ECT Signal circuit at the ECT Sensor harness connector and probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.Start the engine and allow it to reach normal operating temperature.Monitor the voltmeter.Is the voltage below 0.5 of a volt?YesGo To 5NoRepair the open in the (K2) ECT Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)5. EXCESSIVE RESISTANCE IN THE (K900) SENSOR GROUND CIRCUITTurn the ignition off.Move the voltmeter leads to backprobe the (K900) Sensor Ground circuit at the ECT Sensor harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is indicated on the voltmeter.When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.Start the engine and allow it to reach normal operating temperature.Monitor the voltmeter.Is the voltage below 0.5 of a volt?YesGo To 6NoRepair the open in the (K900) Sensor ground circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)6. PCMBefore continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.Were there any problems found?YesRepair as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)NoReplace and program the Powertrain Control Module per Service Information.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)