U012A: Lost Communication With Chassis Control Module A

What it means

ECU lost CAN communication with chassis control module A (vehicle dynamics). 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

Chassis control module A handles vehicle dynamics information and communicates it to other modules over the CAN network. U012A sets when an ECU cannot receive the expected messages from this specific module, so dependent functions may be disabled and other modules may show communication faults. A module power or ground problem, network wiring fault, gateway routing issue, or network termination fault can cause the loss.

Common causes

Most likely first.

1. Module unpowered
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 and communication codes to see which ECUs cannot reach chassis control module A and whether the fault is shared.
2. Check battery condition and charging-system operation, then inspect module A’s power and ground connections for a supply fault.
3. Inspect the CAN wiring and connectors between module A and the network for damage, corrosion, loose pins, or signs of water entry.
4. Check whether the module responds to a scan tool and whether the gateway reports or routes its messages correctly, using vehicle service information.
5. If power, ground, and wiring checks pass, test CAN network termination and signal circuits against the vehicle’s wiring diagram and manufacturer’s specification.

Common fixes

• Correct a weak battery or charging-system fault.
• Restore a loose, corroded, or missing power or ground connection at chassis control module A.
• Repair damaged CAN wiring or connector terminals.
• Correct a confirmed gateway routing or network termination fault according to vehicle service information.
• Replace chassis control module A if its supplies, network wiring, and gateway path test correctly but it remains offline.

Can I keep driving?

Multiple warning lights or disabled chassis functions can affect stability and other driver assistance features. Reduce speed, avoid slippery roads and abrupt manoeuvres, and stop if braking or steering behaviour changes; arrange prompt diagnosis.