For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P1691: Engine Coolant Temperature (ECT) Output Circuit

### Circuit/System Description

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.

### Conditions for Running the DTC

• | The ignition is ON.

• | The ignition 1 voltage is between 10-16 volts.

• | This DTC runs continuously once the above conditions are met.

### Conditions for Setting the DTC

• | The ECM detects that the commanded state of the driver and the actual state of the signal circuit do not match.

• | The above condition must be present for a minimum of 25 seconds.

### Action Taken When the DTC Sets

DTC P1691 is a Type C DTC.

### Conditions for Clearing the DTC

DTC P1691 is a Type C DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

#### Special Tools

J 33431-C Signal Generator and Instrument Panel Tester

### Circuit/System Verification

1. Engine running, observe the DTC information with a scan tool. DTC P1691 should not set.

⇒ | If DTCs P0654 or P0656 are also set, refer to Symptoms - Displays and Gages for further diagnosis of the instrument panel cluster (IPC).

2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the engine control module.
2. Ignition OFF, connect the J 33431-C to the engine coolant temperature gage output signal circuit at the ECM harness connector and a good ground.
3. Ignition ON, set the J 33431-C to generate a speedometer signal. The engine coolant temperature gage should change.

⇒ | If the gage changes, replace the ECM.

⇒ | If the gage does not change, test the engine coolant temperature gage output signal circuit for the following conditions:

• | Open

• | Short to ground

• | Short to voltage

• | High resistance

⇒ | If the circuits test normal, replace the IPC.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Instrument Cluster Replacement

• | Control Module References for engine control module replacement, setup, and programming