Network, generic

U025A Lost Communication With Special Purpose Vehicle Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modeNo

U025A concerns the second slot for special purpose controllers. No manufacturer documents this code publicly. Why more than one slot exists becomes clear from an Audi patent: it describes a configurable control module for police cars, fire engines, taxis or vehicles for disabled occupants, linked through CAN, LIN or other interfaces, that turns a standard car into a commercial vehicle by adding function units. A conversion may thus carry several such boxes, for example one for the light bar and one for a tail lift. GM's 2024 Universal Vehicle Module shows the typical layout of one such unit. A listening module sets U025A when frames from unit B stop; which module listens and how long it waits is not published. Start at the body builder's wiring and fuses. Driving is normally not affected; U055B covers corrupt data.

Likely causes

Second add-on unit unpowered, often via a switched or separately fused upfit circuit
Faulty splice or connector where the conversion joins the vehicle bus
Unit removed or replaced while the vehicle still expects it
Internal failure of controller B

Symptoms

  • Functions of the second conversion unit inoperative
  • Warning or message from the conversion control panel

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–700
Time0.5–3 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

special purpose vehicle module bvehicle bus wiring

Related codes

U055BU0259U025BU025C

References: patents.google.com, gmupfitter.com.