U0029Vehicle Communication Bus A Performance
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- U0029 reports that Vehicle Communication Bus A works, but not reliably; which network that is depends on the maker. In Audi's 48 V mild hybrids (A6 up to Q8, 2019-23) the engine control unit logs U002900 for its sensor/hybrid CAN, labelled there as no communication, together with U002800; the belt starter-generator is then set to freewheel, the battery is no longer charged and a yellow or red battery warning appears. Audi blames connectors not plugged in or locked properly, spread pins or shorted wires, and states that a new starter-generator does not help. The Q5 PHEV stores it after the 12 V wiring feeding its power electronics rubs on the underbody trim. GM names U0029 for 2014-20 full-size trucks and SUVs with a dash harness pinched at the left instrument panel bracket, and for 2017 trucks with a hung gateway module.
- What you may notice
- Yellow or red battery warning, battery not charging (Audi mild hybrid)
- Intermittent warning messages from several systems
- Comfort or infotainment functions drop out briefly
- Likely causes
- LikelyConnector not fully seated or locked, spread or bent pins
- LikelyHarness chafed on underbody trim or pinched at a dash bracket
- PossibleFaulty sensor on the bus disturbing communication (Audi brake servo pressure sensor)
- RareGateway module stops communicating until reset
- Repair
- Hard · Usually a job for a workshop.Typical cost: €60 – €900
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.