For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using the 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 P1629: Theft Deterrent Fuel Enable Signal Not Received

### Circuit/System Description

The theft deterrent module (TDM) sends the fuel enable password to the engine control module (ECM) via the serial data circuit. The ECM then challenges this password. Both the ECM and TDM perform a calculation on this challenge. If the calculated response from the TDM equals the calculation performed by the ECM, the ECM will allow vehicle starting.

### Conditions for Running the DTC

• | Ignition is in the RUN position.

• | The ECM is not in learn mode.

### Conditions for Setting the DTC

The ECM receives does not receive the challenge response from the TDM within 2 seconds.

### Action Taken When the DTC Sets

The security indicator will illuminate.

### Conditions for Clearing the DTC

• | A current DTC P1629 will be cleared when a challenge response is received.

• | A history DTC will be cleared after 40 malfunction-free ignition cycles or when a scan tool is used to clear DTC’s.

### Diagnostic Aids

DTC P1629 is an indicator that the challenge response was not received within the required 2 second window. This does not necessarily indicate a fault is present with the TDM or ECM. Factors such as a long engine crank, a delay in the serial data communication, or B-codes set in the TDM will cause DTC P1629 to set. This DTC should not be used as a fault indicator, but rather as a symptom to assist in the diagnosis of these other systems.

### Reference Information

#### Schematic Reference

Immobilizer Schematics

#### Connector End View Reference

Immobilizer 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

• | Scan Tool Data List

• | Scan Tool Data Definitions