U0291Lost Communication With Gear Shift Control Module B
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- Gear selection at the selector has no effect
- Transmission warning or flashing range display
- Vehicle cannot be shifted out of Park or Neutral
- Likely causes
- LikelyLoose or corroded connector at the second selector
- PossibleBus line to selector B chafed or interrupted
- PossibleSelector variant or software not matching the transmission calibration
- RareSelector module B internally failed
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.