For 1990-2009 cars

### Circuit Description

The powertrain control module (PCM) controls the fuel injector operation based on a vehicle theft deterrent (VTD) password from the vehicle body control module (BCM). When the ignition is first turned ON, the BCM sends a programmed theft deterrent password to the PCM. The PCM acknowledges the password and responds to the BCM that normal fuel injector operation will continue. If the PCM detects an incorrect password, a theft deterrent system failure, or an attempted vehicle theft, DTC P1631 will set. The engine will not start as long as the condition is present.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

• | The PCM detects an incorrect password from the VTD system.

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

### Action Taken When the DTC Sets

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

• | The PCM 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 MIL/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 PCM has learned does not agree with the password received from the VTD system. This condition can occur if the BCM has been replaced and the PCM Password Learn function has not been enabled. If the BCM has been replaced, the password must be relearned.

Step | Action | Yes | No
--- | --- | --- | ---
1 | Did you perform A Diagnostic System Check-Theft Deterrent? | Go to Step 2 | Go to Diagnostic System Check - Theft Deterrent
2 | Perform the Password Learn Procedure. Refer to Programming Theft Deterrent System Components . Did you complete the procedure? | System OK | --