U0035 code meaning
Vehicle Communication Bus A (-) High
What U0035 means
U0035 means the (-) wire of Vehicle Communication Bus A is held too high, typically shorted to battery voltage. On a two-wire high-speed-type CAN, such as Audi's sensor/hybrid CAN filed under Bus A, this is CAN-Low. onsemi's tests place CAN-Low at 12 V among the shorts that make transmission impossible: frames can no longer be sent and the controllers repeat them without success. All modules on Bus A drop out together, and units on other networks register their absence. This is the opposite of U0034, where traffic survives. No manufacturer documents U0035 publicly. Measuring CAN-Low against ground with ignition on shows battery voltage instead of roughly 1.5 to 2.5 V; chafing against a supply wire or a water-filled connector are the usual reasons.
U0035 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0035
- All functions on Bus A fail together
- Lost-communication codes in modules on other networks
- Warning lamps or fallback modes depending on the modules involved
Common causes of U0035
- Most likely(-) wire chafed against a battery or ignition feed
- PossibleWater in a connector linking the (-) wire to a supply pin
- Less likelyDamaged transceiver driving the (-) line high
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus a wiringBus a transceiver
What each part of U0035 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 35 | The exact fault in that area. |
What to do next
- Note U0035 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 U0035
What does U0035 mean?
U0035 means "Vehicle Communication Bus A (-) High". U0035 means the (-) wire of Vehicle Communication Bus A is held too high, typically shorted to battery voltage. It is a generic code, so it means the same on every make.
Is it safe to drive with U0035?
Drive gently and only to a workshop. With U0035 the car can go into limp mode (reduced power) to protect itself.
Will U0035 fail an emissions test?
U0035 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 U0035 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0035 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.