Network, generic

U0291 Lost Communication With Gear Shift Control Module B

Check engine lightUsually off
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

With shift-by-wire, the driver's lever, buttons or dial is an electronic module that sends the selected range to the transmission over the network. Gear shift control module B is a second unit of this kind; U0291 means the transmission controller has stopped receiving its messages. Allison documents the pair for its sixth-generation controls of the 1000 to 4000 series, released in 2021: U0103 covers gear shift module 1, U0291 module 2, with separate codes for incompatibility (U0333) and invalid data (U0592) of the second selector. Mercedes-Benz uses U029100 on the 8-speed dual-clutch transmission 724.1 for a communication fault with the electronic selector lever module. Range changes requested at that selector are then ignored; the transmission typically stays in or returns to a safe range.

Likely causes

Loose or corroded connector at the second selector
Bus line to selector B chafed or interrupted
Selector variant or software not matching the transmission calibration
Selector module B internally failed

Symptoms

  • Gear selection at the selector has no effect
  • Transmission warning or flashing range display
  • Vehicle cannot be shifted out of Park or Neutral

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€50–1,500
Time0.5–3 h

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

Parts involved

gear shift control module bvehicle bus wiring

Related codes

U0103U0592U0404P085E

References: static.nhtsa.gov, static.nhtsa.gov.