U0035
Vehicle Communication Bus A (-) High
Data bus (CAN)
Generic OBD-II
Medium
What it means
U0035 means a module sees the negative wire of Communication Bus A sitting too high — usually shorted to a voltage source instead of switching normally. Bus A is a manufacturer-defined data bus; when its signal is pulled high, the modules on it can lose the ability to talk, so features drop out and warning lights appear.
Medium
Can I keep driving? Often drivable short-term, but modules on Bus A may lose function and set warning lights; a fully disrupted bus can disable systems, so diagnose promptly.
Common symptoms
What you'll notice
- Warning lights on for one or more systems
- Modules on Bus A not responding to a scan tool
- Features tied to Bus A intermittent or inoperative
- Companion U-communication codes stored at the same time
Common causes
Most likely first
- Bus A negative wire shorted to battery or ignition voltageLikely
- Chafed harness contacting a powered wireCommon
- Corroded or water-intruded connectorCommon
- Internal module fault forcing the line highLess often
- Damaged bus wiringLess often
How to diagnose & fix
Work through it in order
- Scan every module and note all communication codes.
- Verify charging system and battery voltage first.
- Inspect Bus A wiring for a short to power and for chafed insulation.
- Measure the bus voltage and resistance key-off to find the line held high.
- Isolate modules one at a time to find a unit forcing the bus high, then retest.
FAQ
Quick answers
Is it safe to drive with U0035?+
Usually for a short trip, but the systems on Bus A may drop out. If several warning lights appear or a system fails, stop and get it checked.
Can I just clear U0035?+
It returns while the wire is shorted high. Find and repair the short before clearing.
Related codes
Often seen with U0035
Read & clear U0035 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX