What does fault code TCM-U003900 mean?

Diagnostic fault code details for TCM-U003900 (Volvo S60 (2011–), Volvo S80 (2007–), Volvo V40 (2013–)). Repair service at OBD Tuning.

VOLVO

TCM-U003900 - Lost Communication With Engine Control Module (ECM) on communication bus "B". General Failure Information. No sub type information

System

Transmission Control Module (TCM)

Volvo models this fault code applies to

Applies to the following models:

9 models

S60 (2011–), S80 (2007–), V40 (2013–), V40 Cross Country (2013–), V60 (2011–), V60 Cross Country (2015–), V70 (2008–), XC60 (2009–), XC70 (2008–)

Show models by year and engine (9)

What does this fault code mean?

The transmission control module (TCM) is receiving no communication from the engine control module (ECM) on bus B. The fault most likely lies in the wiring between the two control modules, but it can also be in the engine control module. The code gives no specific fault type, only that communication has been interrupted.

Possible causes

Brief open circuit or short on the CAN wire linking the engine module (ECM) to the gearbox module (TCM)
Fault in the engine control module (ECM)
Incorrect signal configuration, for example if a control module has been replaced without new software being loaded

What you can do

1Read codes from the engine control module (ECM) and the central electronic module (CEM) and deal with them first
2Clear the code and see whether it comes back; if it does not, the fault was most likely temporary
3Check the connectors and wiring of the CAN network between engine and gearbox for looseness, corrosion and damage
4Have a workshop load new software into the control module if the code is only present in the gearbox

Symptoms you may notice1

No noticeable symptoms for the driver

General guidance for car owners. Diagnosis on the car can point to a different cause.