1000 - 1999: 1231

1231-00 ENGINE COOLANT TEMPERATURE SENSOR CIRCUIT





When Monitored and Set Condition

- When Monitored: With the ignition on.
- Set Condition: The A/C Heater Control Module reports an abnormally high or low voltage that is detected by the Instrument Cluster. The abnormal condition is at the Powertrain Control Module (PCM) on the Engine Coolant Temperature Sensor Signal circuit. The abnormal condition is communicated from the PCM to the Instrument Cluster by the CAN bus.





For a complete HVAC Circuit Diagram, HVAC Schematics and Diagrams.

Diagnostic Test

1. READ ENGINE COOLANT TEMPERATURE SENSOR VOLTAGE WITH scan tool
Turn the ignition on.
With the scan tool, read the Engine Coolant Temperature Sensor voltage.
Does the scan tool display ENGINE COOLANT TEMP: 5.0 VOLTS or greater?

Yes

- Go to 2

No

- Go to 6

2. MEASURE THE VOLTAGE OF THE ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT




Turn the ignition off.
Disconnect the Engine Coolant Temperature Sensor harness connector.

NOTE: Check connector - Clean/repair as necessary.

Turn the ignition on.
Measure the voltage of the Engine Coolant Temperature Sensor Signal Circuit at the Engine Coolant Temperature Sensor harness connector.
Is the voltage above 5.5 volts?

Yes

- Repair the Engine Coolant Temperature Sensor Signal circuit for a short to voltage.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- Go to 3

3. READ ENGINE COOLANT TEMPERATURE SENSOR VOLTAGE WITH scan tool
Turn the ignition off.
Connect a jumper wire between the Engine Coolant Temperature Sensor Signal circuit and the Sensor Ground circuit.
Turn the ignition on.
With the scan tool, read the Engine Coolant Temperature Sensor voltage.
Does the scan tool display ENGINE COOLANT TEMP: 4.5 VOLTS or greater?

Yes

- Go to 4

No

- Replace the Engine Coolant Temperature Sensor. Engine Coolant Temperature Sensor - Removal.
- Perform BODY VERIFICATION TEST. Body Verification Test

4. MEASURE THE RESISTANCE OF THE ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT




Turn the ignition off.
Disconnect the Powertrain Control Module harness connector.

NOTE: Check connector - Clean/repair as necessary.

Measure the resistance of the Engine Coolant Temperature Sensor Signal circuit from the Powertrain Control Module harness connector to the Engine Coolant Temperature Sensor harness connector.
Is the resistance below 5.0 ohms?

Yes

- Go to 5

No

- Repair the Engine Coolant Temperature Sensor Signal circuit for an open.
- Perform BODY VERIFICATION TEST. Body Verification Test

5. MEASURE THE RESISTANCE OF THE SENSOR GROUND CIRCUIT




With the ignition off.
Measure the resistance of the Sensor Ground circuit from the Powertrain Control Module harness connector to the Engine Coolant Temperature Sensor harness connector.
Is the resistance below 5.0 ohms?

Yes

- Replace the Powertrain Control Module. Powertrain Control Module - Removal.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- Repair the Sensor Ground circuit for an open.
- Perform BODY VERIFICATION TEST. Body Verification Test

6. READ ENGINE COOLANT TEMPERATURE SENSOR VOLTAGE WITH scan tool
Turn the ignition off.
Disconnect the Engine Coolant Temperature Sensor harness connector.

NOTE: Check connector - Clean/repair as necessary.

Turn the ignition on.
With the scan tool, read the Engine Coolant Temperature Sensor voltage.
Does the scan tool display ENGINE COOLANT TEMP: 4.5 VOLTS or greater?

Yes

- Go to 7

No

- Go to 9

7. READ A/C HEATER CONTROL MODULE DTC'S WITH scan tool
Turn the ignition off.
Reconnect the Engine Coolant Temperature Sensor connector.
Turn the ignition on.
With the scan tool, read A/C Heater Control Module DTC's.
Wait two minutes.
With the scan tool, read A/C Heater Control Module DTC's.
Does the scan tool display an Engine Coolant Temperature Sensor Failure DTC?

Yes

- Replace the Engine Coolant Temperature Sensor. Engine Coolant Temperature Sensor - Removal.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- Go to 8

8. READ A/C HEATER CONTROL MODULE DTC'S WITH scan tool
Ensure the Engine Coolant Temperature Sensor is connected at this time.
Start the engine.
Turn the A/C system on and run for at least five minutes.
With the scan tool, read A/C Heater Control Module DTC's.
Does the scan tool display an Engine Coolant Temperature Sensor Failure DTC?

Yes

- Replace the Engine Coolant Temperature Sensor. Engine Coolant Temperature Sensor - Removal.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- The condition that caused this DTC to set is currently not present. Inspect the related wiring harness for a possible intermittent condition.
- Perform BODY VERIFICATION TEST. Body Verification Test

9. MEASURE THE RESISTANCE BETWEEN GROUND AND THE ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT




Turn the ignition off.
Disconnect the Powertrain Control Module harness connector.

NOTE: Check connector - Clean/repair as necessary.

Measure the resistance between ground and the Engine Coolant Temperature Signal circuit at the Powertrain Control Module connector.
Is the resistance below 1000.0 ohms?

Yes

- Repair the Engine Coolant Temperature Sensor Signal circuit for a short to ground.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- Go to 10

10. MEASURE THE RESISTANCE FROM THE ENGINE COOLANT TEMPERATURE SENSOR SIGNAL CIRCUIT TO THE SENSOR GROUND CIRCUIT




With the ignition off.
Measure the resistance from the Engine Coolant Temperature Sensor Signal circuit to the Sensor Ground circuit at the Engine Coolant Temperature Sensor harness connector.
Is the resistance below 1000.0 ohms?

Yes

- Repair the Engine Coolant Temperature Sensor Signal circuit for a short to the Sensor Ground circuit.
- Perform BODY VERIFICATION TEST. Body Verification Test

No

- Replace the Powertrain Control Module. Powertrain Control Module - Removal.
- Perform BODY VERIFICATION TEST. Body Verification Test