U0140: Lost Communication with Body Control Module

What it means

CAN messages from the body control module (BCM) are missing. Effects depend on what the BCM controls — typically interior lights, wipers, central locking, immobiliser handshake. On some cars the engine refuses to start because the immobiliser handshake fails.

At a glance

• Usually lights the warning light of the system that lost communication

How it works

The body control module (BCM) communicates with other modules and may manage functions such as interior lighting, wipers, central locking, and immobiliser coordination. U0140 sets when expected messages from the BCM are missing, so the affected functions depend on the vehicle's design.

Common causes

Most likely first.

1. BCM unpowered
2. Water ingress into BCM (often footwell-mounted)
3. Gateway module routing CAN messages incorrectly

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 related communication codes; note whether the fault is accompanied by starting, wiper, lighting, or locking problems.
2. Check battery condition and charging-system operation because low voltage can interrupt BCM communication.
3. Inspect the BCM connector and nearby harness for looseness, corrosion, or water; check for moisture in the surrounding footwell or mounting area.
4. Use the wiring diagram to check BCM power and ground circuits under load against the manufacturer's specification.
5. Test the network wiring and gateway path to the BCM for opens, shorts, or poor connections using the manufacturer's procedure.
6. If power, ground, and network connections are sound, check whether the BCM responds to a scan tool before considering replacement or configuration.

Common fixes

• Restore battery or charging-system performance if voltage is low.
• Repair the source of water ingress and dry or repair affected BCM connectors and wiring.
• Secure or repair loose, corroded, or damaged BCM connectors.
• Repair the BCM's power, ground, or network wiring fault.
• Replace and configure the BCM if it remains unresponsive with sound circuits.

Can I keep driving?

If the vehicle will not start, wipers do not work when needed, or essential lights are affected, do not drive until the fault is addressed. BCM communication loss can disable those functions or interfere with immobiliser authorization.