Circuit Description
The serial data circuit is used to communicate information between each module connected to the serial data line. Each module is assigned a specific recognition code (source ID). This code is used to identify which module is communicating on the serial data line. Modules communicate with others by periodically sending messages on the serial data line. These messages contains specific information (or commands) a system requires to function properly. When a module receives a message it also learns the source ID of the system that sent it. This source ID is used to determine which module actually sent the message and for State of Health (SOH) monitoring. SOH monitoring determines if a module is unable to communicate properly. Modules periodically send a SOH message to each other containing their source ID. If a system fails to receive a SOH message from a module that it communicates with, then a DTC identifying what module did not respond will set. Any module that also cannot communicate properly, will also store the appropriate communication DTC that was assigned to that module.
Conditions for Setting the DTC
| • | The RFA system sends out a State of Health (SOH) message to the Body Control Module (BCM), and no SOH message response was sent back. |
| • | Condition must be present for 5 seconds. |
Action Taken When the DTC Sets
| • | Stores a DTC U1064 in the RFA system. |
| • | No BCM output functions will be available to the RFA system. |
| • | No driver warning message will be displayed for this DTC. |
Conditions for Clearing the DTC
| • | This DTC requires an ignition cycle in order to change from current to history. |
| • | The RFA system receives a SOH message back from the BCM. |
| • | A history DTC will clear after 50 consecutive ignition cycles if the condition for the malfunction is no longer present. |
| • | Use the IPC clearing DTCs feature. |
| • | Use a scan tool. |
Diagnostic Aids
| • | If the problem is an intermittent loss of communications. Carefully inspect the serial data line and related components for the following intermittent conditions: |
| - | There is an intermittent open or short (to ground or voltage) in the serial data line. |
| - | Intermittent loss of communication with the BCM. |
| - | Damaged or loose star connector terminals. |
| • | If the serial data line is shorted to ground or shorted to voltage, all systems connected to the same serial data line will not be able to communicate properly. Systems capable of storing loss of communication DTCs (DTCs with the letter U as a prefix) will have these codes stored in their memory. If a DTC U1064 is stored in the RFA system, check for the same DTC stored in the Instrument Panel Cluster (IPC). The IPC also monitors the SOH message from the BCM. If the IPC has a DTC U1064 stored, check the BCM for an intermittent malfunction. If the BCM system does not have a DTC U1064 stored, check for an open in the serial data line between only the RFA system and the BCM. The RFA system must also be checked for intermittent operation due to a loss of power or ground to the receiver. After repairing a DTC U1064, clear all DTCs from all systems capable of storing this DTC. |
| • | If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur. |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
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This test checks if communications can be established between the scan tool and the BCM
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This test checks for a stored RFA DTC U1255. Conditions that set a DTC U1255 may also set a DTC U1064, therefore always diagnose a DTC U1255 first.
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This test will determine if DTC U1064 was set due to a loss of communications with the RFA system or the BCM. The IPC also communicates with the BCM. If a DTC U1064 is stored in the IPC, the BCM must be diagnosed first.
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This test will check for any opens in the serial data line between the RFA system and the BCM. It also checks for any intermittent malfunctions associated with the serial data line.
Step | Action | Value(s) | Yes | No | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Were you sent here from the Remote Keyless Entry Diagnostic System Check? | -- | ||||||||||||
Does the scan tool communicate with the BCM? | -- | |||||||||||||
Is DTC U1255 stored in the RFA System? | -- | |||||||||||||
Is DTC U1064 stored in the IPC memory? | -- | |||||||||||||
Check the serial data line for the following intermittent conditions:
Was a problem found and repaired? | -- | |||||||||||||
6 |
Does DTC U1064 reset? | -- | System OK | |||||||||||
7 |
Is the replacement complete? | -- | -- | |||||||||||
8 |
Are all repairs complete? | -- | -- |
