Circuit Description
The Vehicle Theft Deterrent (VTD) system consists of the following components:
| • | Powertrain Control Module (PCM) |
| • | Body Control Module (BCM) |
| • | Ignition Lock |
After the Body Control Module (BCM) has confirmed the proper voltage from the ignition switch, 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 loose 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 PCM are restored. If the BCM and PCM loose 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 fuel 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 the diagnostic fails. The PCM stores this information in the Failure Records. |
Conditions for Clearing the DTC
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC will clear after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Use a scan tool in order to clear the DTC. |
Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
The most likely cause of DTC P1626 is a loss of serial data communication from the BCM. Check for a loss of power to the BCM or for other causes of communication loss. Check for the following intermittent conditions on the class 2 circuit:
| • | Open Circuit |
| • | Grounded Circuit |
| • | Circuit shorted to a voltage |
Test Description
The numbers below refer to steps on the diagnostic table.
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A communication problem 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.
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The PCM in VTD Fail Enabled mode indicates that a communication problem 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.
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Inspect for an intermittent problem with the Class 2 circuit if the engine starts and idles.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Does the engine start and idle? | -- | Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent. | ||
Install a scan tool. Is the PCM in VTD Fail Enabled mode? | -- | Go to Diagnostic Aids | ||
|
Important: : Monitor all the DTC status parameters and observe or record any additional DTCs before Clearing the DTCs.
Does the engine start and idle? | -- | Go to Diagnostic Aids | ||
5 | Is DTC P1626 set? | -- | Go to Diagnostic System Check - Theft Deterrent in Theft Deterrent. |
