P1626

Circuit Description
The Vehicle Theft Deterrent system consists of the following components:
^ The Powertrain Control Module (PCM)
^ The Body Control Module (BCM)
^ The Ignition Lock and key
After the Body Control Module (BCM) has confirmed the key resistor pellet, the BCM sends a password to the PCM via the Class 2 Serial Data circuit. When this password matches the password stored in the PCM, the system enables the fuel. If the BCM does not send a password or if the PCM does not receive it, the vehicle will not start unless the PCM is in VTD Fail-Enabled mode. If the BCM and PCM lose communications with each other after the system has received the correct password, the PCM goes into VTD Fail-Enable mode. This allows the driver to restart the vehicle on future ignition cycles until communications between the BCM and the PCM are restored. If the BCM and PCM lose communications before the PCM receives the BCM password, the PCM disables the fuel until communications is restored in order to prevent vehicle theft. In both cases, DTC P1626 sets. The PCM will not disable the fuel injection once the PCM enabled the fuel within a given ignition cycle in order to prevent stalling as a result of VTD system faults.

Conditions for Running the DTC
^ The system has reached the fuel the enable decision point.
^ The PCM is in Failed Enable Mode due to loss of communications with the BCM after the system received the correct password earlier in the ignition cycle.

Conditions for Setting the DTC
The PCM does receive the password message from the BCM prior to the VTD Fuel Decision Point.

Action Taken When the DTC Sets
^ The PCM enables the fuel on future ignition cycles only if the PCM is in Failed Enable Mode.
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time during which the diagnostic fails. The PCM stores this information in the Failure Records.

Conditions for Clearing the MIL/DTC
^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important:
^ Remove any debris from the PCM/TAC module connector surfaces before servicing the PCM/TAC module. Inspect the PCM/TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM/TAC modules.
^ For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter kit J 35616-A. Using this kit prevents damage to the harness/component terminals.
^ The most likely cause of DTC P1626 is a loss of serial data communication from the BCM. Inspect for a loss of power to the BCM or for other causes of communication loss. Inspect for the following intermittent conditions on the class 2 circuit:
- Poor connections
- Open Circuit
- Grounded Circuit
- Shorted to a voltage
^ For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. A communication condition exists if the engine does not start and DTC P1626 sets. The PCM disables the fuel control if the PCM does not receive the password from the BCM before the engine is started.
3. The PCM in VTD Fail Enabled mode indicates that a communication condition occurred while the engine was operating. The engine will continue to operate if the PCM does not receive the password from the BCM while the engine is operating.
4. Test for an intermittent condition with the Class 2 circuit if the engine starts and idles.