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 Class2 serial data line send out a periodic identifier message. The PCM is listening for the identifier messages from the EBCM and the BFC 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 can not communicate with the Body Function Controllor (BFC) and the Electronic Brake Control Module (EBCM) or can recieve but can not send.
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 Failure Records buffer. |
| • | 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. |
| • | A scan tool can clear the MIL/DTCs. |
Diagnostic Aids
| • | Move the PCM and BFC connectors while watching the IPC to see if serial data is lost. When serial data is lost, the IPC telltales are illuminated. This is a good indication that serial data is lost to the BFC. |
| • | An intermittent problem may be caused by electrical interference on the ground circuit of the IPC, a poor connection, rubbed through wire insulation, or a wire that is broken inside the insulation. |
| • | Any circuitry, that is suspected as causing the intermittent complaint, should be thoroughly checked for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed |
| - | Damaged terminals |
| - | Poor terminal to wire connection |
| • | Install an additional ground wire from the IPC to the negative side of the battery if electrical interference is suspected. |
| Refer to Electrcial Diagnosis of the service manual for additional diagnostic information. |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The Powertrian 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.
-
A scan tool that cannot display PCM data indicates that a short, or open may exist on the serial data circuit. Refer to Data Link Connector Diagnosis portion of the service manual for further diagnosis.
-
An intermittent short on the EBCM serial data circuit could cause this DTC to set. When the malfunction is present, the scan tool will lose communication with the PCM. Check for chaffed wiring or a malfunctioning EBCM.
-
The DTC is intermittent when a scan tool can communicate with the PCM. DTCs within the BFC or EBCM may lead to a possible cause of the intermittent problem.
-
If the serial data loss occurred after a good theft password has been received, the PCM will allow the vehicle to be started on following attempts. After making the necessary repairs to the vehicle the PCM must be reprogrammed and the password learn procedure and the crankshaft position system variation procedures must be completed to allow the theft system to operate properly, Refer to the Powertrain Control Module (PCM) portion of the service manual for the reprogramming procedures.
-
If no malfunctions have been found at this point and no additional DTCs were set, refer to Diagnostic Aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | |||
Install a scan tool. Can the scan tool display data from the PCM? | -- | |||
3 | Check for a poor connection, open, or shorted serial data circuit to the Body Function Controller (BFC)and repair as necessary. Was a repair necessary? | -- | ||
Check for an intermittent short on the EBCM serial data circuit and repair as necessary. Was a repair necessary? | -- | |||
Check for DTCs or communication with the other modules and make any necessary repairs. Is the action complete? | -- | -- | ||
Does the scan tool indicate that this diagnostic ran and passed? | -- | |||
Check if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK, refer to Diagnostic Aids |
