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 engine control module (ECM) controls the fuel injector operation based on a theft deterrent password from the body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed theft deterrent password to the ECM. The ECM acknowledges the password and responds to the BCM that normal fuel injector operation will continue. If the ECM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC 1631 will set. The engine will not start as long as the condition is present.

### Conditions for Running the DTC

Ignition is in the RUN position.

### Conditions for Setting the DTC

• | The ECM detects an incorrect password from the theft deterrent system.

• | The condition is present for less than 1 second.

### Action Taken When the DTC Sets

• | The ECM will not illuminate the malfunction indicator lamp (MIL).

• | The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

### Conditions for Clearing the DTC

• | A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

• | The DTC can be cleared by using a scan tool.

### Diagnostic Aids

DTC P1631 indicates that the vehicle theft deterrent password that the ECM has learned does not agree with the password received from the theft deterrent system. This condition can occur if an incorrect key is used when attempting to start the vehicle, or if the BCM has been replaced and the ECM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.

### Reference Information

#### Schematic Reference

Immobilizer Schematics

#### Connector End View Reference

Master Electrical Component List

#### 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

• | Scan Tool Data List

• | Scan Tool Data Definitions

### Circuit/System Testing

Perform the password learn procedure. Refer to Programming Theft Deterrent System Components .

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for BCM replacement, setup, and programming