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. 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 Powertrain Control Module (PCM) is listening for the identifier messages from the following modules:
| • | Electronic brake control module (EBCM) |
| • | Body control module (BCM) |
| • | Instrument panel cluster (IPC) |
If the PCM does not receive an identifier message from a module, the PCM assumes that there is a loss of communication and a DTC is stored. A DTC P1626 will set after the engine has been started, theft has passed, and there is lost of communication between the PCM and the BCM. Since this DTC P1626 set after the engine has been started, the theft protection is bypassed at subsequent key ups. The vehicle will start, but as long as DTC P1626 is set there is no theft protection.
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. |
| • | A scan tool can 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 the following conditions:
| • | Poor electrical terminal connection |
| • | Broken wire inside the insulation |
Thoroughly check any suspected circuitry for the following items:
| • | Backed out terminals or improper mating |
| • | Improperly formed or damaged terminals |
| • | Poor terminal to wiring connections |
| • | Physical damage to the wiring harness |
| • | Corrosion |
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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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 malfunction occurred. The information is then stored in the scan tool for later reference.
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If the serial data circuit to the Body Control Module (BCM) was not open, then the serial communication loss to the PCM lies within the BCM. Refer to Body Control Module System Check Passlock diagnosis.
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The replacement PCM must be reprogrammed and the crankshaft position system variation procedure must be performed. Refer to the latest Techline procedures for PCM reprogramming and Crankshaft Position System Variation Learn for the Crankshaft Position Variation Procedure.
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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 Crankshaft Position System Variation Learn portion of the service manual for the reprogramming procedures.
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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? | -- | Go to Step 2 | ||||||
2 |
Was DTC P1626 Current? | -- | ||||||
3 |
Is DTC P1626 still Current? | -- | ||||||
4 | Check if DTC U1064 is set with the scan tool. Is DTC U 1064 also set? | -- | ||||||
5 | Check if DTC U1064 is Current or in History with the scan tool. Is DTC U1064 Current? | -- | ||||||
6 |
Is DTC U1064 Current? | -- | ||||||
7 | Attempt to communicate with the Body Control Module (BCM) with the scan tool. Can you communicate with the BCM? | -- | ||||||
Check for any Body Control Module (BCM) DTCs with the scan tool. Are there any BCM DTCs set? | -- | |||||||
9 | Does the Body Control Module (BCM) indicate the password is valid? | -- | ||||||
10 | Attempt to communicate to Electronic Brake Control Module (EBCM) and the IPC with the scan tool. Can you communicate to the Electronic Brake Control Module (EBCM) and IPC with the scan tool? | -- | ||||||
11 |
Was a repair necessary? | -- | ||||||
12 | Attempt to communicate to the BCM with the scan tool. Can you communicate with the BCM with the scan tool? | -- | ||||||
13 |
Was a repair necessary? | -- | ||||||
14 | Perform the Password Learn Procedure. Refer to Password Learn . Is the action complete? | -- | -- | |||||
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 |
