Circuit Description
The serial data circuit is used to communicate information between each system connected to the serial data line. Each system is assigned a specific recognition code (source ID). This code is used to identify which system is communicating on the serial data line. Systems communicate with others by periodically sending messages on the serial data line. These messages contain specific information (or commands) a system requires to function properly. When a system receives a message it also learns the source ID of the system that sent it. This source ID is used to determine which system actually sent the message and for State of Health (SOH) monitoring. SOH monitoring determines if a system is unable to communicate properly. Systems periodically send a SOH message to each other containing their source ID. If a system fails to receive a SOH message back from a system that it communicates with, then a DTC identifying what system did not respond will set.
Conditions for Setting the DTC
| • | A system sends out a (SOH) message on the serial data line to the Instrument Panel Cluster (IPC), and no SOH message response was sent back. |
| • | Condition must be present for 5 seconds. |
Action Taken When the DTC Sets
| • | Stores a DTC U1096 in the system that was unable to communicate with the IPC. |
| • | The system unable to communicate with the IPC may set false DTCs and substitute default values for certain functions. |
| • | 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. |
| • | A system sends out a (SOH) message on the serial data line to the IPC, and a SOH message response was sent back. |
| • | 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 IPC. |
| - | Damaged or loose star connector terminals. |
| - | Poor connections/terminal tension at a harness connector. |
| - | Intermittent IPC communication due to a loss of power or ground to the IPC. |
| • | Communication DTCs do not necessarily indicate a malfunction. These DTCs are only intended to aid in diagnosing an intermittent communication malfunction that is accompanied by a symptom. If the vehicle does not experience a symptom related to a communication malfunction, these DTCs can be disregarded. |
| • | 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 U1096 is stored in a system's memory, check for the same DTC stored in other systems capable of setting a DTC U1096. The RFA, LDCM, RDCM, and BCM all monitor the SOH message from the IPC. If other systems have a DTC U1096 stored, check the IPC for an intermittent malfunction. If other systems do not have a DTC U1096 stored, check for an intermittent malfunction in the system that set a DTC U1096. After repairing a DTC U1096, clear all DTCs from all systems capable of storing communication DTCs. |
| • | 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 determines if communications can be established between the scan tool and the BCM. The BCM is responsible for sending ignition position status on the serial data line. This information is utilized by certain systems to enter a wake-up state. The BCM must be diagnosed first if the scan tool cannot communicate with the BCM. Refer to Diagnostic System Check - Body Control System in Body Control System.
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This test determines if communications can be established between the scan tool and the IPC. If the scan tool cannot communicate with the IPC. Refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console.
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This test determines if communications can be established between the scan tool and the system that set the DTC U1096. If the scan tool intermittently cannot communicate with the system that stored a DTC U1096, the IPC is not cause the malfunction and the applicable system must be diagnosed first. Refer to the appropriate Diagnostic System Check.
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This test for any opens in the serial data line between the system that set a DTC U1096 and the IPC. It also checks for any intermittent malfunctions associated with the serial data line.
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This test will determine if DTC U1096 was set due to a loss of communications with the IPC. If the malfunction is due to a intermittent loss of communications with the IPC, other systems capable of storing a DTC U1096 may have this DTC stored.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Were you sent here from the Data Link Communications Diagnostic System Check? | -- | ||||||||||
Does the scan tool communicate with the BCM? | -- | |||||||||||
Communicate with the IPC. Does the scan tool communicate with the IPC? | -- | |||||||||||
Using a scan tool, attempt to establish communications with the applicable system that set a DTC U1096. Does the scan tool communicate with the applicable system? | -- | |||||||||||
Test the serial data line for the following intermittent conditions:
Was a problem found and repaired? | -- | |||||||||||
Using a scan tool, observe for a DTC U1096 set in other systems capable of storing this DTC. Is a DTC U1096 set in any of the specified systems? | BCM RFA LDCM RDCM | |||||||||||
7 | Test for intermittent operation/communications in the applicable system that set the DTC U1096. Refer to the applicable Diagnostic System Check. Was a problem found and repaired? | -- | Go to Diagnostic Aids | |||||||||
8 | Test for intermittent IPC operation. Refer to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console. Is the repair complete? | -- | -- | |||||||||
9 |
Is the repair complete? | -- | -- |
