U0086Vehicle Communication Bus F (-) Low
- Generic OBD-II code · Network
- Can trigger limp mode
- How the car detects it
- U0086 says the (-) wire of Vehicle Communication Bus F sits too low, usually shorted to ground. On a FlexRay Bus F, as in the Audi A6/A7, that wire is bus minus (BM). At rest both FlexRay lines float near half the transceiver supply, and NXP specifies a near-zero difference between them in idle. A grounded BM leaves BP well above it, a permanent positive difference that receivers read as DATA_1 instead of idle, which disturbs wake-up and frame recognition across the cluster. On a CAN the comparable fault, CAN-Low to ground, is usually harmless for traffic and stays hidden unless a transceiver with bus diagnosis reports it, as NXP describes. No manufacturer documents U0086 publicly. Measure the (-) wire to chassis with the battery disconnected.
- What you may notice
- Modules on Bus F fail to wake or drop out
- On CAN layouts often no noticeable symptom
- Likely causes
- Likely(-) wire of Bus F chafed against body metal
- PossibleHarness trapped under a seat rail or trim
- RareTransceiver of one module pulling the (-) line to ground
- Repair
- Hard · Usually a job for a workshop.Typical cost: €60 – €800
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.