Circuit Description
The serial data circuit is used in order to communicate between the powertrain control module (PCM) and the vehicle theft deterrent body control module (BCM) systems.
When the Passlock™ portion of the Vehicle Theft Deterrent (VTD) System has sensed the proper operation of the ignition switch and lock, or determined that the switch and lock have not been tampered with, the BCM transmits a password to the PCM. Fuel delivery is enabled if this password matches the password stored in the modules memory. If a component in the theft deterrent system has been replaced, the modules need to relearn the password of the new components. If the relearn procedure was not performed, this diagnostic trouble code (DTC) will set.
If a VTD failure occurs during an ignition cycle that the PCM has enabled fuel, then the BCM will enter a fail-safe mode: Fail Enable VTD System Failure with Fuel Enabled. The BCM remains in Fail Enable Mode, for the current and future ignition cycles, until the fault is corrected and a valid password is received, or until battery power is removed. If the battery is disconnected or the codes are cleared, the vehicle will lose its Fail Enable status and will not start until the fault is corrected, the ten minute timer expires, and the PCM receives the correct fuel delivery password.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1631 Theft Deterrent Start Enable Signal Not Correct
Conditions for Running the DTC
| • | DTC P1626 is not active. |
| • | The PCM is not in password learn mode. |
| • | The VTD Passlock™ System is enabled. |
| • | The fuel enable decision point has been reached, or the engine is cranking. |
Conditions for Setting the DTC
The PCM did not receive a valid password before the fuel disable decision point was reached.
Action Taken When the DTC Sets
| • | The PCM stores the DTC in history after the first failure but will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores the failure information in the scan tools Freeze Frame/Failure Records. |
| • | The Service Vehicle Soon (SVS) light may be illuminated. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. |
| • | A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle. |
| • | Use the scan tool Clear Information function. |
Diagnostic Aids
Important: Do not clear DTCs unless directed by a diagnostic procedure. Clearing DTCs will also clear valuable Freeze Frame and Failure Records data.
| • | If the PCM is replaced, the PCM must re-learn a valid password and crankshaft variation. |
| • | If the BCM is replaced, the PCM must re-learn a valid password. |
| • | Check for published service bulletins relating to exhibited symptoms or component operation. |
| • | If the vehicle does not start, or starts and stalls: |
| - | Turn OFF the ignition and wait at least 5 seconds before trying to restart. |
| - | If a fault or tamper has been detected, the BCM will not forward the correct password to the PCM for a period of ten minutes, even if the condition is corrected during that time period. This may cause a DTC P1631 to set in the PCM. This timer can be monitored in the Passlock™ Data parameter of the scan tool. Once the time has elapsed, the BCM will determine if the condition is still present. |
| • | The PCM and BCM parameters can be monitored with a scan tool. |
| • | The Passlock™ state and the auto learn timer can be viewed in the Passlock™ Data parameter of the scan tool. |
| • | Check the following for preventing the Passlock™ sensor from communicating with the BCM: |
| - | Passlock sensor |
| - | Ignition switch assembly |
| - | Passlock sensor circuitry |
| - | Bent pins at the small Passlock™ sensor |
| • | If this DTC sets along with a DTC B2960, then the problem was caused by malfunctioning Passlock™ components or circuitry, not the PCM. |
| • | Inspect all related wiring and connections including the PCM and BCM connections. These may cause an intermittent malfunction. |
| • | An intermittent may be caused by any of the following conditions: |
| - | A poor connection |
| - | Rubbed through wire insulation |
| - | A broken wire inside the insulation |
| • | Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections . |
If a repair is necessary, refer to Wiring Repairs or Connector Repairs .
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This DTC may set as a result of other Passlock™ System problems. Diagnose any BCM DTCs prior to continuing with this diagnostic.
-
A DTC B3031 may set in the BCM during the Password Learn Procedure.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Data Communication Schematics | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
|
Important: You must diagnose the Bxxxx codes prior to diagnosing any Pxxxx code.
Does the scan tool display DTC P1631 as a current DTC? | Go to Step 3 | Go to Testing for Intermittent Conditions and Poor Connections | |
Perform the Passlock™ Programming procedure. Refer to Immobilizer System Component Programming . Did the powertrain control module (PCM) successfully learn the password? | Go to Step 4 | ||
4 |
Important: Before clearing DTCs, monitor all DTC status parameters and note any additional DTCs.
Does the engine start and operate normally? | System OK | Go to Step 2 |
