CAN network

U0104 — Lost Communication with Cruise Control Module

Severity: low Safe to drive

What U0104 means

A control unit has detected that the cruise control module (conventional or adaptive, ACC) is no longer sending messages on the CAN bus. This module normally exchanges data constantly with the speed, brake and engine systems. When its messages stop, the unit flags it as offline and stores U0104.

Symptoms

  • Cruise control will not engage or cancels itself
  • ACC or cruise system warning message in the cluster
  • Check engine or other warning lights on
  • Distance control or collision warning features unavailable
  • Other modules may also log communication errors

Possible causes

  1. Failed cruise control module or ACC radar unit
  2. Open, shorted or chafed CAN bus wiring
  3. Corroded or damaged module connectors
  4. Blown fuse or loss of power or ground to the module
  5. Low battery voltage or weak charging system
  6. Radar sensor damaged or misaligned after a bumper impact or repair

How to diagnose

  1. Scan all modules and look for other U-codes or network faults
  2. Test battery voltage and alternator output
  3. Check fuses and relays feeding the cruise or ACC module using the wiring diagram
  4. Inspect the radar sensor, front bumper and connector for damage, water and corrosion
  5. Verify power and ground at the module connector with a multimeter
  6. Test the CAN-H and CAN-L lines for continuity, resistance and shorts
  7. Clear the code and see if it returns immediately or only under certain conditions
  8. If wiring and power are good, test the module with a scan tool or swap in a known good one and program it

Common fixes

  • Charge or replace the battery and repair any charging fault
  • Replace the blown fuse and fix the cause of the overload
  • Repair wiring and clean or replace connectors
  • Realign or replace the radar sensor and calibrate it
  • Replace the cruise control module and code or program it

Questions and answers

What does U0104 mean?

It means communication with the cruise control module was lost on the CAN bus. Other modules stopped receiving its data, so cruise control is usually disabled.

Can I drive with a U0104 code?

Usually yes, but without cruise control and related driver aids. Do not put off diagnosis too long, in case it points to a power or network problem.

Can a weak battery cause U0104?

Yes, low voltage often causes temporary communication drops between modules. Check the battery and alternator first, then clear the code and see if it comes back.

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.