U007A: Control Module Communication Bus H Off

What it means

The control module communication bus H 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 H carries data among the vehicle modules connected to that network. The control module monitors bus H communication, and this code sets when the network is off or isolated, often after repeated errors have put its CAN controller into a bus-off state.

Common causes

Most likely first.

1. CAN controller in bus-off state from repeated errors
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. Save all codes and freeze-frame data, then identify which bus H modules are offline and whether the CAN controller reports repeated errors or a bus-off state.
2. Inspect bus H wiring, connectors, and grounds for damage, corrosion, loose pins, or shorts that could cause repeated frame errors.
3. Check gateway data for bus H isolation or routing faults and note whether the bus drops out intermittently or remains off.
4. With the network powered down as specified by the manufacturer, test bus H wiring for continuity and shorts and verify termination against the manufacturer's specification.
5. If wiring and termination pass, isolate bus H modules using the manufacturer's procedure to find a faulty controller or gateway disrupting traffic.

Common fixes

• Repair damaged, loose, or corroded bus H wiring and connectors.
• Correct poor module or gateway connections that interrupt bus H traffic.
• Replace a terminating resistor if testing shows it is outside the manufacturer's specification.
• Repair or replace the gateway if it incorrectly isolates or routes bus H.
• Repair or replace a module whose CAN controller repeatedly forces bus H into bus-off.

Can I keep driving?

Because bus H is off and limp mode may occur, avoid high-speed or long-distance driving and do not rely on affected vehicle functions. Stop driving if essential controls or safety systems are impaired; continued operation can leave more modules without required data.