P1626

Circuit Description
A Class II 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.

Conditions for Running the DTC
The VTD system has allowed fuel delivery.

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

Action Taken When the DTC Sets
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.
^ A history DTC is stored.

Conditions for Clearing the MIL/DTC
^ A history DTC will clear after 40 consecutive warm up cycles without a fault.
^ DTCs can be cleared by using a scan tool.

Diagnostic Aids
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:

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.

^ Intermittent short circuit on the serial data circuit. Refer to Scan Tool Does Not Communicate with Components in Data Link Communications. Be sure to check all related wiring for an intermittent short to ground or short to voltage.
^ Poor connection. Inspect the PCM and BFC harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
^ Damaged harness. Inspect the wiring harness for damage. Check for an intermittent short or open circuit in the wiring harnesses related to the BFC, including the ignition, battery feed, ground, and serial data circuits.

Refer to Testing for Continuity, Intermittents and Poor Connections Diagnosis. Symptom Related Diagnostic Procedures

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.

Test Description
The numbers below refer to the step numbers 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 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.