P1631

Diagnostic Chart:

Wiring Diagram:

CIRCUIT DESCRIPTION

The Class II serial date circuit is used to communicate between the VCM and the VTD (Passlock)/Electronic Variable Orifice (EVO) Control Module systems.

When the Passlock portion of the Vehicle Theft Deterrent System (VTD) system has sensed the proper operation of the ignition switch and lock (determines that the switch and lock have not been tampered with), the Passlock system transmits a password to the VCM. The VCM enables fuel delivery if this password matches the password stored in VCM memory. However; if communication is lost or a VTD failure occurs (during an ignition cycle that the VCM has enabled fuel) the VCM will enter a fail-safe mode: Fail Enable (VTD System Failure with Fuel Enabled). The VCM remains in Fail Enable mode, for the current and future ignition cycles, until the fault is corrected and a valid pass word is received, or until battery power is removed. If the battery power is removed while the VCM is in the Fail Enable mode (ignition ON or OFF) the VCM disables fuel delivery. The vehicle will not start, or it will start then stall.

When the VCM receives an invalid password or no password, before the Fuel Disable Decision Point, the VCM disables fuel delivery. The Fuel Disable Decision Point occurs at about 300 RPM during the engine crank mode.

CONDITIONS FOR SETTING THE DTC

^ DTC P1626 is not set.

^ The VCM is not in password Learn Mode.

^ A number of invalid passwords have been received by the VCM, before the Fuel disable Decision Point.

^ The VCM has established communications with the VTD (Passlock) Control Module and received a valid password, during this ignition cycle.

^ The VCM cannot re-establish communications, no Node alive/SOH messages received, with the VTD (Passlock) Control Module for 5 seconds.

OR

The VCM cannot establish communications with the VTD (Passlock) Control Module and has not received a valid password before the Fuel Disable Decision Point.

ACTION TAKEN WHEN THE DTC SETS

^ The vehicle does not start, or it starts then stalls.

^ A DTC P1631 is stored in the VCM memory.

^ The VCM will not illuminate the MIL.

^ The Security lamp may be illuminated by the VTD (Passlock) system.

^ The VCM disables fuel delivery until the fault is corrected and a valid password is received from the VTD (Passlock) Control Module.

CONDITIONS FOR CLEARING THE MIL/DTC

^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (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.

^ Disconnect the VCM battery feed for 30 seconds.

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 VCM is replaced, the VCM must re-learn a valid password and Crankshaft variation.

^ If the VTD (Passlock) Control Module is replaced, the VCM must re-learn a valid password.

^ Check for published service bulletins relating to exhibited symptoms or component operation.

^ Inspect all related wiring and connections including the VCM and VTD (Passlock) Control Module connections. These may cause an intermittent malfunction

^ Thoroughly check any circuit that can cause an intermittent complaint for the following:

- Backed out terminals

- Improper mating

- Broken locks

- Improperly formed or damaged terminals

- Poor terminal to wiring connections

- Physical damage to the wiring harness

- Corrosion

^ If the vehicle does not start, or starts and stalls:

- Turn OFF the ignition and wait at least 5 seconds before trying to restart.

- When the VCM receives a password from the 'VTD (Passlock) Control Module that does not match the stored password, a DTC P1631 should be present. Check for VTD codes first; if no codes are present, then force a relearn of the password. Refer to Password Learn Procedure.

^ Monitor the VCM's VTD (Passlock) parameters with a scan tool.

^ The scan tool's Diagnostic Circuit Check can be used to:

- Monitor the Class II Serial Data circuit for Node Alive/SOH messages.

- Monitor for loss of communications DTCs (DTCs with the letter U as a prefix).

- Clear loss of communications DTCs.

^ The scan tool's Diagnostic Circuit Check's Active status indicates that the module is communicating with the scan tool; Inactive indicates that a module that had established communications with the scan tool is not currently communicating. If a module is not listed at all, then the missing module never successfully established communications with the scan tool; refer to Electrical Diagnosis for any unlisted modules.

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the diagnostic table.

3. The 11 minute and 30 second time criteria, are a minimum required amount of time. The time limit can exceed this limit, without interfering with the Auto Learn Procedure. A scan tool can be used (VTD Auto Learn Timer equals Inactive) to determine when the 11 minutes has expired.

8. If DTC P1631 is set, indicates that the procedure was not followed correctly. The Re-learn procedure will have to be re-performed.