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 P1631: Theft Deterrent Fuel Enable Signal Not Correct

### Circuit/System Description

The body control module (BCM) sends the fuel enable password to the engine control module (ECM) via the serial data circuit. The ECM compares this password to the learned password. If the learned password matches the password received from the BCM, the ECM will allow vehicle starting.

### Conditions for Running the DTC

Ignition is in the ACCESSORY or RUN position.

### Conditions for Setting the DTC

The ECM receives an incorrect fuel enable password from the BCM.

### Action Taken When the DTC Sets

• | The security indicator will illuminate.

• | Vehicle starting will be disabled.

### Conditions for Clearing the DTC

• | A current DTC will be cleared when a correct fuel enable password is received.

• | A history DTC will be cleared after 40 malfunction-free ignition cycles.

### Reference Information

#### Schematic Reference

Immobilizer Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Immobilizer Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

Important: Because of normal system communications between the TDM and ECM, any theft deterrent B-codes must be diagnosed prior to the diagnosis of P-codes.

Perform the 10-Minute Immobilizer Relearn procedure. Refer to Immobilizer System Component Programming . The ECM should successfully complete the password learn and the vehicle should start.

⇒ | If the ECM does not complete the learn or vehicle starting remains disabled, replace the ECM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup and programming