DTC P1668 Engine Coolant Temperature (ECT) Output Circuit

The engine control module (ECM) creates the engine coolant temperature gage output signal by pulsing the circuit to ground. The ECM monitors the voltage on the engine coolant temperature gage output circuit. If the ECM determines that the voltage is out of the normal operating range, a DTC sets.

The engine is running.

The ECM detects an open, short to ground, or a short to voltage on the temperature gage output circuit.

DTC P1668 is a Type C DTC.

DTC P1668 is a Type C DTC.

Schematic Reference

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Special Tools

J 33431-C Signal Generator and Instrument Panel Tester

With the engine idling for 1 minute, observe the DTC information with a scan tool. DTC P1668 should not set.

1. Ignition ON, observe the DTC info with a scan tool. Verify that DTCs P0654, and P0656 are not also set.

⇒	If DTCs P0654 and P0656 are also set, test the ignition 1 voltage circuit and the ground circuit of the instrument panel cluster (IPC) for an open, short to ground, or high resistance.

⇒	If the circuits/connections test normal, replace the IPC.

2. Ignition OFF, disconnect the harness connector of the ECM.
3. Install the J 33431-C between the output circuit of the temperature gage and the negative terminal of the battery.
4. Ignition ON, set the J 33431-C to generate a speedometer signal. Verify the temperature gage operation.

⇒	If the temperature gage does not operate, test the output circuit of the temperature gage for an open, short to ground, short to voltage, or a high resistance. If the circuit/connections test normal, replace the IPC.

5. If all circuits/connections test normal, replace the ECM.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.