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
DTC P1691 01: Engine Coolant Temperature (ECT) Output Circuit Short to Battery
DTC P1691 02: Engine Coolant Temperature (ECT) Output Circuit Short to Ground
DTC P1691 04: Engine Coolant Temperature (ECT) Output Circuit Open Circuit
DTC P1691 54: Engine Coolant Temperature (ECT) Output Circuit Temperature High

### Circuit/System Description

The engine control module (ECM) controls the engine coolant temperature (ETC) gage by pulsing the control circuit to ground at a predetermined hertz rate. The ECM monitors the voltage on the engine coolant temperature (ECT) output circuit. If the ECM determines the voltage is out of the normal operating range or detects a high temperature condition, a DTC sets.

### Conditions for Running the DTC

• | The ignition is ON.

• | The ignition voltage is between 8.5-16.5 volts.

• | DTC P1691 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P1691 01

The ECM detects a short to voltage on the control circuit.

#### P1691 02

The ECM detects a short to ground on the control circuit.

#### P1691 04

The ECM detects an open on the control circuit.

#### P1691 54

The ECM detects that the internal output driver is over temperature.

### 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

### Circuit/System Verification

1. Engine idling, observe the scan tool DTC information parameter. DTC P1691 should not set.
2. Engine idling at the normal operating temperature. Compare the scan tool ECT sensor parameter with the engine coolant temperature gage on the instrument panel cluster (IPC). The temperatures should match.
3. 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 ECM.
2. Connect the J 33431-C to the engine coolant temperature gage output signal circuit terminal XK67 at the ECM harness connector and 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 and repair the signal circuit for the following conditions:

• | An open

• | A short to ground

• | A short to voltage

• | A high resistance

4. If all 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