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 PCM cannot communicate with the theft deterrent system.

Attempting to start the vehicle by bypassing the theft deterrent system or substituting parts without performing the password learn procedure may set a DTC P1631.

If no password is received a DTC P1610, P1626 and P1631 may be set.

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation.

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for the following items:

If the Body Function Controller (BFC) is replaced the PCM must be reflashed to allow the new password to be learned. Refer to Password Learn Procedure . The ignition must be turned off for at least 30 seconds then on for the PCM to learn the new BFC password.

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. Refer to Powertrain Control Module Replacement/Programming , Crankshaft Position System Variation Learn and Password Learn Procedure for reprogramming procedures.

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 Control Module System Check in Body Control System.

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.