P1631
Diagnostic Chart:
Wiring Diagram:
CIRCUIT DESCRIPTION
The Vehicle Theft Deterrent (VTD) System, called a Passlock II System, is designed to prevent vehicle theft by disabling the engine unless the Passlock lock cylinder is correctly engaged by a mechanical key. The Passlock II System utilizes four components for theft detection: the lock cylinder, the ignition switch, the Truck Body Controller (TBC) and the Powertrain Control Module (PCM).
When starting the engine, the PCM looks for a password from the TBC through the Class 2 serial data circuit. If the password is not recognized or not present, the PCM will disable the engine. If an incorrect or no Password received, this indicates that the engine will start and stall immediately. THEFT SYSTEM telltale will flash on the PC for approximately 4 seconds. If an incorrect or Disable Password Received, (More than three invalid passwords are received) this indicates that the engine is disabled for at least 10 minutes and that the THEFT SYSTEM telltale will flash on the PC for approximately 4 seconds then illuminate solid on the Instrument Panel Cluster (IPC) for the 10 minutes. After the vehicle has passed theft detection, the PCM will continue a normal engine operation. If the PCM loses the TBC communication within the same ignition cycle, the vehicle will continue to run on the following ignition cycles. This mode is called the fail enable mode. Additional information can be found in the Passlock Theft Deterrent Systems.
CONDITIONS FOR SETTING THE DTC
An unrecognized or incorrect password is sent to the PCM from the TBC.
ACTION TAKEN WHEN THE DTC SETS
^ The PCM will record operating conditions at the time during which the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.
^ A history DTC stores.
^ The engine fueling is disabled by the PCM.
CONDITIONS FOR CLEARING THE MIL/DTC
^ A history DTC will clear after 40 consecutive warm up cycles without a fault.
^ A scan tool can clear the DTC(s).
DIAGNOSTIC AIDS
Attempting to start the vehicle by bypassing the Passlock II system or by substituting parts without performing the password learn procedure may set a DTC P1631 and a P1532.
If no password is received, a DTC U1064 and P1632 may be set.
An intermittent may be caused by a poor connection, a rubbed through wire insulation, or by a wire broken inside the insulation.
Thoroughly check any suspected circuitry for the following items:
^ Backed out terminals or improper mating.
^ Broken locks.
^ Improperly formed or damaged terminals.
^ Poor terminal to wiring connections.
^ Physical damage to the wiring harness.
^ Corrosion.
TEST DESCRIPTION
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data captured when the fault occurred. The information then stores in the scan tool for later reference.
2. The scan tool can display whether or not the TBC has received and learned the password from the lock cylinder. If the password is not received, the reason the PCM set this DTC may due to a password that has not yet been learned due to a component being replaced, or a problem in the TBC or a VTD component.
3. The theft deterrent password resides in the Truck Body Controller (TBC). Anytime a VTD component is replaced, the Powertrain Control Module (PCM) must relearn the new TBC password.
4. A TBC Passlock theft deterrent DTC being set indicates that a Passlock II component may be malfunctioning. Refer to the applicable TBC table for diagnosis.
5. If no vehicle theft deterrent DTCs were set and the TBC has not learned (received) a password from the ignition lock cylinder, the TBC may need to learn the password or be malfunctioning.
6. Replacement PCMs must be reprogrammed. A reprogrammed PCM does not require the password learn procedure to be performed. The password will be learned on the first ignition cycle. Refer to the latest Techline information for programming procedures. Reprogram the replacement PCM and perform the crankshaft position system variation learning procedure. Refer to the latest Techline procedures for PCM reprogramming and the Crankshaft Position (CKP) System Variation Learn Procedure portion of the service manual for the crankshaft position variation learning procedure.
8. If no malfunctions are present at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.