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U1040 – What Does It Mean and How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


U1040 is an OBD-II Code that refers to Lost Communication with Electronic Brake Control Module


A U1040 code is a diagnostic trouble code that occurs when the other control modules on the vehicle are not communicating with each other. In this instance the Controller Area Network bus communications, or simply CAN indicates there’s a loss of communication with the EBCM which is responsible for the electronic braking system and controls functions such as the anti-lock braking system, traction control, and stability control. 


Common causes for this code include:

  • Faulty Electronic Brake Control Module (EBCM)
  • Electronic Brake Control Module (EBCM) harness is open or shorted
  • Electronic Brake Control Module (EBCM) circuit poor electrical connection


The symptoms of a U1040 code are:

  • Illuminated Check Engine Light
  • ABS Light may be illuminated
  • Traction Control Light may be illuminated
  • Stability Control Light may be illuminated
  • Brake Lights may stay on
  • Vehicle may have reduced braking power


To diagnose a U1040 DTC code, a technician would:

  1. Scan for codes in the ECM and look at the freeze frame data for failure.
  2. Visually inspect the Electronic Brake Control Module (EBCM) and the harness for signs of physical damage.
  3. Use a voltmeter to test the Electronic Brake Control Module (EBCM) power and ground circuits.
  4. Test the CAN bus system for communication issues.

Common mistakes

The following are some of the most common mistakes that a technician may make when diagnosing a U1040 code:

  • Not thoroughly inspecting all the wiring and connectors.
  • Not checking the fuses.
  • Not properly testing the EBCM circuit.
  • Reinstalling the EBCM without properly testing it.

How serious is this?

A U1040 code in most cases is a more serious issue and should be addressed as soon as possible. Depending on the symptoms, a vehicle with this code may not be safe to drive. 

What repairs can fix the code?

The following are solutions that may fix this problem:

  • Repair or replace any faulty parts such as wiring, connectors, or control modules
  • Check and/or replace any blown fuses
  • Reinstall the EBCM and properly test it
  • View and check the Factory Service Manuals

Related codes

A U1040 is related to and may be accompanied by the following codes:

U1041 – Lost Communication with Fuel Pump Control Module

U1042 – Lost Communication with Heated Oxygen Sensor Control Module

U1043 – Lost Communication with Ignition Coil Control Module

U1044 – Lost Communication with Multiplex Control Module


In conclusion, the U1040 code is a diagnostic trouble code that refers to a problem with the communication between different control modules on the vehicle. The code may be accompanied by other related codes, and can cause various symptoms such as illuminated warning lights or reduced braking power. If you suspect that your vehicle has this code, it is important to have it diagnosed and repaired as soon as possible.