CAN network

U0142 — Lost Communication with Body Control Module B

Severity: medium Drive with care, to a shop

What U0142 means

A control unit on the vehicle network has stopped receiving messages from Body Control Module B (the secondary BCM) and stored U0142. Modules normally exchange data over the CAN bus and must answer regularly. If the BCM has no power, a broken bus line, or an internal fault, its functions become unavailable.

Symptoms

  • Random electrical problems
  • Door locks not working or acting on their own
  • Exterior or interior lighting faults
  • Several warning lamps on at once
  • Functions controlled by this module unavailable
  • Possible battery drain

Possible causes

  1. Low battery voltage or poor battery terminals
  2. Loss of power or ground at BCM B
  3. Corroded connectors or terminals
  4. Damaged, chafed, or open CAN wiring, including behind the dash
  5. Water intrusion into the module or its connector
  6. Failed BCM B
  7. Another faulty module loading the bus

How to diagnose

  1. Test battery voltage and terminal condition; charge or replace the battery if needed
  2. Run a full-module scan to see which modules are not responding and whether other U codes are stored
  3. Inspect BCM B, its connectors, and harness for water, corrosion, and chafing
  4. Check fuses, power, and ground circuits for the module using the wiring diagram
  5. Measure voltages and resistance on CAN H and CAN L at the diagnostic connector (typically about 60 ohms across the pair)
  6. Test the CAN wiring from the module to the bus for opens and shorts
  7. Unplug suspect modules one at a time only if the manufacturer's procedure allows it
  8. If power, ground, and the bus are good, test or replace BCM B and program it to the vehicle

Common fixes

  • Charge or replace the battery and clean the terminals
  • Restore power and ground to the module, replace a blown fuse
  • Repair the CAN harness and replace damaged connectors
  • Dry and clean the module after water intrusion and fix the leak
  • Replace or reflash BCM B and code it to the vehicle

Questions and answers

What does U0142 mean?

It means communication with Body Control Module B on the CAN bus has been lost. Other modules get no response from it, so its functions may not work.

Can I drive with U0142?

Usually yes, with caution. If lighting or signals are affected, fix the problem first, and keep an eye on battery drain.

What most often causes U0142?

Common causes are a weak battery, corroded connectors, lost power or ground at the module, and damaged CAN wiring. A failed BCM is less common and should be confirmed only after everything else is checked.

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.