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 did not "learn" a SOH message and recognition code from any of the following systems: |
| - | Body Control Module (BCM) |
| - | Powertrain Control Module (PCM) |
| - | Instrument Panel Cluster (IPC) |
| • | This DTC can only set when the ignition is first turned ON. |
| • | Condition must be present for 5 seconds. |
Action Taken When the DTC Sets
| • | Stores a DTC U1000 in the RFA system. |
| • | Will substitute default values for certain parameters. |
| • | 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, IPC and PCM. |
| • | 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, IPC or PCM. |
| - | Damaged or loose star connector terminals. |
| - | There is a loss of communications when the ignition is first turned ON. |
| • | 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 U1000 is stored in the RFA memory when the ignition is first turned ON, check for other communication DTC and diagnose them first. If the RFA system looses communications with a system after the SOH message was received, the RFA system will identify this system by storing the appropriate communication code that was associated to that system. Always diagnose them first before diagnosing a DTC U1000. |
| • | 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 if communications can be established between the scan tool and the IPC.
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This test checks if communications can be established between the scan tool and the PCM.
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This test checks for a stored RFA DTC U1255. Conditions that set a DTC U1255 may also set a DTC U1000, therefore always diagnose a DTC U1255 first.
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This test checks for any communication DTCs stored in the RFA system. Any history or current communication DTCs that are stored in the RFA system will assist in diagnosing a DTC U1000. Always diagnose them first before diagnosing a DTC U1000.
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This test will check for any opens in the serial data line between the RFA system and the BCM, PCM or IPC. 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 RFA Diagnostic System Check? | -- | ||||||||||||
Does the scan tool communicate with the BCM? | -- | |||||||||||||
Using a scan tool, attempt to establish communications with the IPC. Does the scan tool communicate with the IPC? | -- | |||||||||||||
Using a scan tool, attempt to establish communications with the PCM. Does the scan tool communicate with the PCM? | -- | |||||||||||||
Is DTC U1255 stored in the RFA System? | -- | Go to DTC U1255 Diagnostic Table | ||||||||||||
Select display RFA DTCs function with the scan tool. Are any of the specified communication DTC stored in the RFA system? | DTC U1016 DTC U1064 DTC U1096 | Go to the Applicable DTC Table | ||||||||||||
Check the serial data line for the following intermittent conditions:
Was a problem found and repaired? | -- | |||||||||||||
8 |
Does DTC U1000 reset? | -- | System OK | |||||||||||
9 |
Is the replacement complete? | -- | -- | |||||||||||
10 |
Are all repairs complete? | -- | -- |
