CAN network

U0140 — Lost Communication with Body Control Module (BCM)

Severity: medium Drive with care, to a shop

What U0140 means

U0140 means one or more control modules stopped receiving data from the Body Control Module (BCM). The BCM manages lighting, door locks, windows, the immobilizer and other comfort and security functions, and it shares information with other modules over the CAN bus. When its messages disappear, a loss-of-communication code is stored.

Symptoms

  • Check engine light or several warning lights on the dash
  • Lights, door locks or power windows not working properly
  • Interior or exterior lights flickering or switching on and off randomly
  • Key fob or keyless entry not working
  • No-crank condition or security light on
  • Other body (B) codes or additional communication codes stored

Possible causes

  1. Low battery voltage or poor terminal connections
  2. Open, shorted or chafed CAN bus wiring
  3. Corroded or loose BCM connectors
  4. Blown BCM fuse or poor ground
  5. Water intrusion and corrosion inside the BCM
  6. Failed BCM
  7. Another faulty module pulling down or loading the CAN bus

How to diagnose

  1. Scan all modules and note which ones have lost communication
  2. Test battery voltage and charging output, and charge the battery if needed
  3. Check the fuses and relays that power the BCM
  4. Inspect the BCM and its connectors for moisture, corrosion or loose pins
  5. Verify power and ground at the BCM connector with a multimeter
  6. Measure CAN bus resistance (typically about 60 ohms) and CAN-H and CAN-L voltages at the diagnostic connector
  7. Inspect the harness for chafing, especially in flex areas such as door jambs
  8. Unplug suspect modules one at a time only if the manufacturer's procedure allows it

Common fixes

  • Charge or replace the battery and clean the terminals
  • Replace blown fuses and restore proper power and ground
  • Repair damaged CAN wiring and connectors
  • Dry and clean a water-damaged BCM and fix the source of the leak
  • Replace and program the BCM if it has failed

Questions and answers

What does U0140 mean?

It means communication with the Body Control Module has been lost, so other modules are not receiving its data over the CAN bus. The cause can be the module itself, its power supply or the wiring.

Should I replace the BCM right away for U0140?

No. Check the battery, fuses, grounds, connectors and CAN wiring first. These fail far more often than the module itself.

Can I drive with a U0140 code?

If the car starts normally and the lights and gauges work, you can usually drive it to a shop. There is a risk of sudden lighting or starting problems, so don't put the repair off.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.