Circuit Description
A Class 2 serial data communications system is used on this vehicle in order 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 for the reduction of the vehicle wiring, and for the transmission and reception of multiple signals over a single wire. The messages carried on the Class 2 serial data stream 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.
All modules on the Class 2 serial data line send out a periodic identifier message. The PCM is listening for the identifier messages from the EBCM and the body control module (BCM), as well as an echo of the PCM identifier message. If a module cannot respond to the PCM, a DTC is stored.
Conditions For Setting the DTC
The PCM has lost communication with the body control module (BCM) after the PCM received a theft passed message from the BCM.
Action Taken When the DTC Sets
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers. |
| • | A history DTC stores. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm up cycles without a fault. |
| • | Use a scan tool to clear the DTCs. |
Diagnostic Aids
Attempting to start the vehicle by bypassing the Passlock ll system or by substituting parts without performing the password learn procedure may set a DTC P1631 and a P1632.
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 broken wire inside the insulation.
Thoroughly inspect 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 numbers below refers to the step numbers on the diagnostic table:
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
2 | Was DTC U1064 also set? | -- | Go to DTC U1001-U1254 Lost Communication with XXX in Data Link Communications | |
3 | Has any part of the vehicle theft deterrent system been tampered with? | -- | ||
4 |
Did you complete the repair? | -- | -- | |
5 | Does the BCM indicate that the password is valid? | -- | ||
|
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming Did you complete the replacement? | -- | -- | ||
7 | Repair the BCM DTCs as necessary . Did you complete the repair? | -- | ||
8 |
Does the scan tool display any DTCs? | -- | System OK |
