U0140 – Lost Communication With Body Control Module

What does U0140 mean?

A module has lost communication with the body control module (BCM). The BCM manages lighting, power windows, locks, wipers, and many convenience features, and it relays information to other modules across the network.

What causes U0140?

Listed from most to least common:

1. 1Damaged CAN bus wiring
2. 2Loss of power or ground at the BCM
3. 3Blown fuse
4. 4Corroded connector or water intrusion — BCMs are often mounted low in the cabin where leaks collect
5. 5Low system voltage
6. 6Failed body control module

Code breakdown

Common symptoms

• Multiple warning lights on simultaneously
• Power windows, locks, interior lights, or wipers not working
• Dashboard warning lights behaving erratically
• Scan tool cannot communicate with the BCM
• Vehicle may fail to start on some models

How to diagnose

1. 1Check battery voltage first — low voltage causes communication dropouts that look like module failure.
2. 2Check all BCM-related fuses.
3. 3Verify power and ground at the BCM connector.
4. 4Inspect for water intrusion. BCMs are frequently mounted under the dash or near the kick panel, where a leaking windshield seal or clogged drain can soak the connector.
5. 5Measure CAN bus resistance across the bus wires.
6. 6Check whether other modules report communication faults to identify the affected segment.

Multiple convenience and lighting systems may stop working simultaneously. On some vehicles this can affect starting or immobilizer function.

Common fixes and estimated costs

Costs are rough US estimates including parts and labor. Actual pricing varies significantly by vehicle, region, and shop rates.

Good to know

Water intrusion is a leading cause. If the vehicle has had a leaking sunroof drain, windshield seal, or heater core, check for moisture at the BCM before considering module replacement — which usually requires programming and key relearning.

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