U007B: Control Module Communication Bus I Off

What it means

The control module communication bus I is off — the gateway has shut down or isolated this bus, often due to repeated bus errors or a "bus off" event in the CAN controller.

At a glance

• Usually lights the warning light of the system that lost communication
• The engine or gearbox may go into limp mode

How it works

Bus I is the network that carries messages between its connected modules. The control module monitors bus I traffic; this code sets when that bus is off, commonly after communication errors leave a CAN controller in a bus-off state.

Common causes

Most likely first.

1. CAN controller in bus-off state
2. Gateway module routing CAN messages incorrectly
3. CAN terminating resistor (120 Ω) drifted out of spec

Symptoms

• Multiple warning lights may illuminate
• Affected modules may go into limp mode or shut down
• Specific functions inoperative depending on module
• Diagnostic tools may show communication faults

How to diagnose it

1. Record all codes and freeze-frame data, then check which bus I modules respond and whether their CAN controllers report bus-off or repeated errors.
2. Inspect bus I wiring, connectors, and grounds for damage, corrosion, loose connections, and shorts that could interrupt data.
3. Review gateway status for bus I routing or isolation faults and correlate it with the modules that are unavailable.
4. With power disconnected as directed by the manufacturer, test bus I wiring for continuity and shorts and check termination against the manufacturer's specification.
5. If the wiring and termination pass, isolate bus I modules according to the manufacturer's procedure to identify a controller or gateway that is disrupting communication.

Common fixes

• Repair damaged or shorted bus I wiring.
• Clean, secure, or repair loose or corroded bus I connectors.
• Replace a terminating resistor if it fails the manufacturer's specification.
• Repair or replace the gateway if it incorrectly routes or isolates bus I.
• Repair or replace a module confirmed to be forcing bus I into a bus-off state.

Can I keep driving?

Limp mode or loss of functions may occur while bus I is off, so avoid demanding driving and do not rely on affected systems. Stop if essential controls or safety functions are impaired; continued driving can worsen the loss of communication.