U3015: Control Module Ground C

What it means

Fault on the third ground reference of the module. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.

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

Ground C is the module's third ground reference, providing a return path for its electrical circuits. U3015 sets when that ground path is faulty, which can destabilize the module's operation or communication with other systems.

Common causes

Most likely first.

1. Ground stud corroded
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. Scan all modules and save freeze-frame data to see whether the ground C fault is accompanied by communication or module reset codes.
2. Inspect the ground C wire, terminal, and ground stud for looseness, corrosion, heat damage, or a broken conductor.
3. Check live module voltage or reset status while gently moving the ground C harness to look for intermittent changes.
4. Measure voltage drop across the ground C path while the module is operating and compare it with the manufacturer's specification.
5. If the ground connection tests correctly, inspect the module connector and check network communication for a separate gateway or CAN fault.

Common fixes

• Clean corrosion from the ground C terminal and mounting point, then secure the connection.
• Repair a damaged ground C wire or terminal.
• Restore a poor ground stud connection and protect it from renewed corrosion.
• Address a confirmed gateway or CAN fault if ground C tests correctly.

Can I keep driving?

A poor module ground can cause intermittent shutdowns or loss of dependent functions, so avoid driving if it affects steering, braking, engine control, or another safety-related system. If the vehicle stalls or critical warnings appear, stop safely.