U0085 code meaning
Vehicle Communication Bus F (-) Open
What U0085 means
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.
U0085 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0085
- Individual modules on Bus F stop responding
- Code present with little or no effect when a second channel takes over
Common causes of U0085
- Most likely(-) wire of Bus F broken after chafing or repeated flexing
- PossibleSpread or corroded terminal of the (-) wire
- Less likelyPoor earlier repair splice in the bus pair
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus f wiringModule connector
What each part of U0085 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 85 | The exact fault in that area. |
What to do next
- Note U0085 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0085
What does U0085 mean?
U0085 means "Vehicle Communication Bus F (-) Open". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with U0085?
Drive gently and only to a workshop. With U0085 the car can go into limp mode (reduced power) to protect itself.
Will U0085 fail an emissions test?
U0085 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0085 to fix?
Difficulty: hard. A typical repair takes 0.5 to 5 hours of work. This is a job for a workshop.
Will U0085 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.