DTC P1668. Chevrolet Joy 2008

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 P1668 Engine Coolant Temperature (ECT) Output Circuit

### Circuit 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 engine is running.

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets

DTC P1668 is a Type C DTC.

### Conditions for Clearing the MIL/DTC

DTC P1668 is a Type C DTC.

### Reference Information

#### Schematic Reference

• | Engine Controls Schematics for the 0.8L engine

• | Engine Controls Schematics for the 1.0L engine

#### Connector End View Reference

• | Engine Control Module Connector End Views for the 0.8L engine

• | Engine Control Module Connector End Views for the 1.0L engine

• | Engine Controls Connector End Views for the 0.8L engine

• | Engine Controls Connector End Views for the 1.0L engine

#### 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

#### Special Tools

J 33431-C Signal Generator and Instrument Panel Tester

### Circuit/System Verification

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

### Circuit/System Testing

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.

### 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