CAN network

U0143 — Lost communication with a control module on the CAN bus

Severity: medium Drive with care, to a shop

What U0143 means

One control module has stopped answering other modules on the CAN network. Modules normally exchange short messages constantly, and when those messages disappear the fault is logged. The exact module named by U0143 depends on the manufacturer: some references list it as Body Control Module "C", others as the parking brake module. Confirm it in the service data for your vehicle.

Symptoms

  • Random electrical faults
  • Other U-codes stored at the same time
  • Several warning lamps on
  • Features of the offline module not working (lighting, locks, parking brake, etc.)
  • Some switches or the instrument cluster acting up

Possible causes

  1. Failed control module (BCM or another)
  2. Open, shorted or chafed CAN bus wiring
  3. Water intrusion in the module or connector
  4. Corroded terminals and connectors
  5. Missing power or ground at the module
  6. Another faulty module loading the bus
  7. CAN backbone damage after a collision or repair

How to diagnose

  1. Run a full-system scan and map which modules respond and which do not
  2. Check fuses and relays that feed the affected module
  3. Inspect the module's connectors and harness for moisture, corrosion and damage
  4. Test the module's power and ground with a multimeter
  5. Measure resistance between CAN-H and CAN-L at the diagnostic connector (about 60 ohms is normal)
  6. Check CAN-H and CAN-L voltages
  7. Unplug suspect modules one at a time only per a documented procedure
  8. Compare against service documentation or a known-good module before replacing

Common fixes

  • Repair or replace the damaged CAN wiring section
  • Clean or replace corroded connectors and terminals
  • Restore the module's power and ground
  • Replace the failed module and program/code it
  • Fix the source of water entry and dry the connectors

Questions and answers

What does U0143 mean?

A control module lost communication with the rest of the CAN network. Which module depends on the manufacturer, most often the BCM or the parking brake module. Check the factory documentation for the exact name.

Can I drive with U0143?

Usually yes, with care, but the module's functions may not work and other systems may act unpredictably. Do not drive if the brakes, lights or steering are affected.

How do I find the cause of U0143?

Start with the module's power, ground and connectors, then check CAN bus resistance and voltages. If the wiring is fine, suspect the module itself.

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.