Circuit Description
The serial data communications system allows various modules to communicate and share information with each other. Each bit of information has one of two lengths: long or short. This reduces the vehicle wiring, and provides for the transmission and reception of multiple signals over a single wire. The messages carried on the 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 serial data line send out a periodic identifier message. The PCM is listening for the identifier messages from the EBCM and the 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 cannot communicate with the EBCM for a duration of 15 seconds after having previously established communications with the EBCM within that ignition cycle. |
| • | The ignition switch in the crank position for 15 seconds and the engine is not rotating due to a starter malfunction or an electrical malfunction. |
Action Taken When the DTC Sets
| • | The PCM will record operating conditions at the time the DTC sets. This information will be stored in the Failure Records buffer. |
| • | A history DTC is stored in the PCM and IPC. |
Conditions for Clearing the DTC
| • | A PCM history DTC will clear after 40 consecutive warm up cycles without a malfunction. |
| • | An IPC history DTC will clear after 100 consecutive ignition cycles without a malfunction. |
| • | The condition responsible for setting the DTC no longer exists and the scan tool Clear DTCs function is used. |
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 connection |
| • | Rubbed through wire insulation |
| • | Broken 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 refer to the step numbers 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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A scan tool that cannot display PCM data indicates that a short, or open may exist on the serial data circuit. Refer to Scan Tool Does Not Communicate with Components for further diagnosis.
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An intermittent short on the body control module (BCM) 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 BCM.
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The DTC is intermittent when a scan tool can communicate with the PCM. DTCs with other modules may lead to a possible cause of the intermittent problem.
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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 Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 2.4L or Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 3.1L | ||||||||
Can the scan tool display data from the PCM? | -- | |||||||||
3 |
Was a repair necessary? | -- | ||||||||
Was a repair necessary? | -- | |||||||||
Test for DTCs or communication with the other modules and make any necessary repairs. Is the action complete? | -- | -- | ||||||||
6 |
Does the scan tool indicate that this diagnostic ran and passed? | -- | ||||||||
Test if any additional DTCs are set. Are any DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 2.4L or Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 3.1L |
