A Class Il serial data communications system is used on this vehicle to allow various modules to communicate and share information with each other. Each bit of information has one of two lengths: long or short. This allows vehicle wiring to be reduced and the transmission and reception of multiple signals over a single wire. The messages carried on a Class II serial data streams are also prioritized. If two messages attempt to establish communications on the data line at the same time, the message with the higher priority will continue. The message with the lower priority message will wait. If a module cannot respond to the PCM, a DTC is stored.

The VTD system has allowed fuel delivery.

The PCM has detected a loss of the state of health serial data message from the VTD system.

Important: Several BFC diagnostic procedures call for disconnecting the BFC and then turning the vehicle ignition to the RUN position. These procedures will result in the PCM setting DTC P1626. Therefore, DTC P1626 stored in history may be the result of previous BFC diagnostic work.

For complete serial data line schematics and VTD system diagnosis, refer to Electrical Diagnosis.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following conditions:

Refer to Testing for Continuity , Intermittents and Poor Connections Diagnosis , Repairing Connector Terminals and Connector Repairs in Wiring Systems.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Number(s) below refer to the step number(s) on the Diagnostic Table:

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. A scan tool that cannot display PCM data indicates that a short exists on the serial data circuit.

6. The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed.

   If the serial data loss occurred after a good theft password has been received, the PCM must be reprogrammed and the password learn and the crankshaft position variation learn procedures must be completed to allow the theft system to operate properly.

7. If the serial data circuit to the Body Function Controller (BFC) was not open, then the serial communication loss to the PCM lies within the BFC. Refer to Body Function Controller portion of the service manual for Passlock diagnosis.

9. If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.