Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Normal Operation and Fault Conditions
With the ignition ON, the FCIM sends messages to the ABS module through the GWM over the MS-CAN. If the ABS module does not receive these messages within a certain time frame (usually less than 1 second), the module sets DTCs. For information on the messages sent to the ABS module by the FCIM, refer to the Description and Operation in the Anti-Lock Brake System (ABS) and Stability Control article.
| DTC | Description | Fault Trigger Conditions |
|---|---|---|
| U0256:00 | Lost Communication With Front Controls Interface Module 'A' | Sets in continuous memory and on-demand when the ABS module is missing any of the FCIM messages. This can be due to a FCIM failure, a circuit failure on the MS-CAN or an excessive load on the network. |
| U0557:86 | Invalid Data Received From Front Controls Interface Module 'A': Signal Invalid | This DTC sets if the auto hold switch status message from the FCIM contains 'invalid' or 'faulted' instead of the actual switch state. This can be due to a FCIM failure, a circuit failure on the MS-CAN or an excessive load on the network. |
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.