U0085Vehicle Communication Bus F (-) Open
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- U0085 points to a severed (-) conductor on Vehicle Communication Bus F, that is bus minus (BM) where Bus F is FlexRay, as in the Audi A6/A7, or CAN-Low in a CAN. How hard the break hits depends on the topology. FlexRay may run two independent channels, and Wikipedia notes that traffic can carry on with reduced bandwidth when one of them fails, so a break on one channel may cost little more than redundancy. In a single-channel layout every node beyond the break goes silent. Transceivers cannot see an open wire directly, as NXP explains for CAN; the module infers it from missing frames. Volvo's truck bulletin KC-2079 also lists open CAN-Low as a trigger of U008088. No manufacturer documents U0085 itself. Check continuity of the (-) wire through every connector.
- What you may notice
- Individual modules on Bus F stop responding
- Code present with little or no effect when a second channel takes over
- Likely causes
- Likely(-) wire of Bus F broken after chafing or repeated flexing
- PossibleSpread or corroded terminal of the (-) wire
- RarePoor earlier repair splice in the bus pair
- Repair
- Hard · Usually a job for a workshop.Typical cost: €60 – €700
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.