U1900 - FAULT CODE - OBD2

POST UPDATED IN February, 2023

U1900 Code failures by brands

U1900 FORD, MERCURY: CAN COMMUNICATION BUS FAULT.

Description of DTC code U1900

The OBDII DTC U1900 is a manufacturer-specific code that is set when the Powertrain Control Module (PCM) finds a breakdown to communicate with itself, the ABS Control Module, the instrument cluster, and the trailer brake controller when the car is on, and it is also in drive position. Although the CAN (Control Area Network) bus connects all the control modules, the U1900 code specifically refers to communication failures in the circuits connecting the PCM to the ABS Control Module and the instrument cluster.

In summary, the CAN bus is a system that allows high-speed communication of all the vehicle control modules. As a result, the information on operating conditions is shared through a very complex wiring system.

The PCM, instrument cluster, and ABS Control Module are connected to two specific CAN bus circuits, 1908 and 1909, they do not accept faults like the rest of the CAN. Therefore, if there are intermittent connections or out-of-range values, they will be interpreted as faults in the communication, so the code 1900 OBD2 will be set.

Symptoms of fault code U1900

  • Check Engine light ON.
  • The Anti-lock Braking System (ABS) light illuminates.

Causes of OBD2 U1900

Reasons for setting the U1900 OBDII fault code:

  • CAN circuits 1908 or 1909 may have damage to the wiring or connectors.
  • The trailer brake control system may not be installed correctly on vehicles with ABS
  • The trailer brake controller may be in bad condition.
  • The ABS Control Module or the instrument cluster may have damaged electrical connections.

Possible solutions of the DTC code U1900

Steps to troubleshoot the U1900 OBD2 diagnostic code:

  • Consult the TSB (Technical Service Bulletins).
  • Refer to the service manual to locate the wiring for CAN bus circuits 1908 and 1909. Once located, verify there are no burned, corroded, or worn wires. Make any necessary repairs or changes.
  • If your vehicle has the ABS system, verify the trailer brake control is in good condition. If you detect problems in this system, consult the steps indicated by the manufacturer to make the necessary corrections.
  • Check the ABS Control Module and Instrument Cluster wiring. If you discover common damage, make any required repairs or changes.

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