CAN network

U0122 — Lost Communication with Vehicle Dynamics Control Module

Severity: medium Drive with care, to a shop

What U0122 means

U0122 is set when a control unit stops receiving messages from the vehicle dynamics control (VDC/ESC) module over the CAN bus. Normally the modules constantly share data on a two-wire network, including wheel speeds, steering angle and brake signals. When that link is lost, stability and traction control usually shut down.

Symptoms

  • ABS and ESC/traction control lights on
  • ESC off indicator lit
  • Several warning lights on at the same time
  • Reduced stability on wet or slippery roads
  • Scan tool cannot communicate with the VDC module
  • Functions that depend on the module unavailable

Possible causes

  1. Damaged, chafed or corroded CAN bus wiring or connectors
  2. Failed VDC/ESC module
  3. No power or ground at the VDC module (blown fuse, bad terminal)
  4. CAN bus short to power or ground, or an open circuit
  5. Another faulty module disrupting the bus
  6. Low system voltage from a weak battery or charging problem
  7. Wheel speed sensor problems affecting the module

How to diagnose

  1. Run a full scan of all modules and note which ones respond and which do not
  2. Test battery voltage and charging system output
  3. Check fuses and relays that feed the VDC module
  4. Inspect the module connector and harness for corrosion, water, chafing or past repairs
  5. Check power and ground at the module connector with a multimeter
  6. Measure resistance between CAN-H and CAN-L at the diagnostic connector (about 60 ohms is normal)
  7. Check CAN line voltages relative to ground
  8. Unplug suspect modules one at a time only when the manufacturer's procedure allows it

Common fixes

  • Repair or replace damaged CAN wiring and connectors
  • Correct power and ground faults: fuse, cleaning battery terminals
  • Update module software if an applicable service bulletin exists
  • Replace the VDC/ESC module and code it to the vehicle
  • Replace any other module that is pulling down the bus

Questions and answers

What does U0122 mean?

It means communication with the vehicle dynamics control module was lost on the CAN bus. Other modules no longer receive its messages, so stability control and related systems may be disabled.

Can I drive with U0122?

Yes, but with care. Stability control, traction control and possibly ABS may be unavailable, which is risky on wet or slippery roads. Get it diagnosed soon.

What should I check first for U0122?

Start with battery voltage, fuses and the VDC module connector, then check power, ground and CAN bus resistance. Wiring or a corroded connector is more often at fault than 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.