DTC P1626 Theft Deterrent Fuel Enable Signal Lost. Cadillac Concours 1996

For 1990-2009 cars

### Circuit Description

After the key resistor pellet has been confirmed by the Passkey portion of the Vehicle Theft Deterrent System (VTD), the IPC sends a password to the PCM via the Class 2 Serial Data Bus. If this password matches the password stored in the PCM, fuel will be enabled. If the IPC does not send a password or if the PCM doesn't receive it, the vehicle will not start unless the VTD system has Fail-Enabled. If the IPC and PCM loose communication with each other while the engine is running the VTD system will Fail-Enable and allow the driver to restart the vehicle on future ignition cycles until communications between the IPC and PCM are restored. If the battery is disconnected during this period, the vehicle will loose its Fail-Enable status and will no longer start until communications has been reestablished. If the IPC and PCM loose communications with each other while the engine is not running, the VTD system will disable fuel until communications is restored to prevent vehicle theft. In both cases DTC P1626 will be set. The PCM will not disable fuel injection once it has been enabled within a given ignition cycle to prevent stalling as a result of VTD system faults.

### Conditions for Setting the DTC

#### Test Conditions

• | Vehicle Theft Deterrent (VTD) system is enabled.

• | Fuel enable decision point has been reached.

#### Failure Conditions

• | The system has Fail-Enabled due to a loss of communications while the engine is running.

| OR

• | No password message is received by the PCM from the IPC prior to the VTD Fuel Decision Point.

### Action Taken When the DTC Sets

• | The PCM enables fuel on future ignition cycles only if the failure occured when the engine was running.

• | The Malfunction Indicator Lamp (MIL) will not illuminate.

• | The PCM will command a message to be displayed.

• | The PCM may record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records.

### Conditions for Clearing the Message/DTC

• | The PCM will turn the message OFF after one run and pass of the diagnostic test.

• | A History DTC will clear after forty consecutive warm-up cycles with no failures of any non-emission related diagnostic test.

• | A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.

• | Use a scan tool to clear DTCs.

• | Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

### Diagnostic Aids

The most likely cause of DTC P1626 is a loss of serial data communication to the IPC. Check for loss of power to the IPC or for other causes of communication loss.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to A Powertrain On Board Diagnostic (OBD) System Check
2 | Is DTC P1604 also set? | -- | Go to DTC P1604 Loss of IPC Serial Data | Go to Step 3
3 | Check for Vehicle Theft Deterrent or IPC DTC's. Are any DTC's set? | -- | Go to DTC(s) that are set | Refer to Diagnostic Aids