Circuit Description
The serial data circuit is used to communicate information between systems. Each system connected to the serial data line is assigned its own recognition code (address). This code is used to identify which module or systems are communicating. Systems communicate with others by periodically sending a State of Health (SOH) message to each other. The RFA system monitors the serial data line for an open or short (to ground or voltage) condition. If the RFA system detects any of these malfunctions as current, no communications will be established between the RFA system and other systems, and the RFA system will store a serial data line malfunction code.
Conditions for Setting the DTC
| • | The RFA system detects an open or short (to ground or voltage) on the serial data line circuit. |
| • | Condition must be present for 1 seconds. |
Action Taken When the DTC Sets
| • | Stores a DTC U1255 in 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 no longer detects an open or short (to ground or voltage) on the serial data line circuit. |
| • | 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 short (to ground or voltage) in the serial data line. |
| - | 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 U1255 is stored in the RFA system, check for the same DTC stored in other systems capable of storing this DTC. If other systems have a DTC U1255 stored, check the serial data line circuit for an open or short (to ground or voltage). After repairing a DTC U1255, 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:
-
This test checks if communications can be established between the scan tool and the other systems connected to the same serial data line.
-
This test will check for any opens or shorts (to ground or voltage) in the serial data line. 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 other systems? | -- | |||||||||||
Check the serial data line for the following intermittent conditions:
Was a problem found and repaired? | -- | |||||||||||
4 |
Does DTC U1255 reset? | -- | System OK | |||||||||
5 |
Is the replacement complete? | -- | -- | |||||||||
6 |
Are all DTCs cleared? | -- | -- |
