What it means
Bus A low-side line voltage above the expected range. Short to power or transceiver fault. A communication loss with this module breaks any function relying on its data — diagnostic tools may show 'no response' and dependent modules can fall into limp mode.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Bus A's negative conductor, commonly CAN-Low on a CAN network, carries one side of the differential signal. U0035 sets when that line is above its allowed voltage range, which can occur if it is shorted to power or a faulty transceiver pulls it high and disrupts communication.
Common causes
Most likely first.
- CAN-L shorted to battery
- Gateway module routing CAN messages incorrectly
- CAN terminating resistor (120 Ω) drifted out of spec
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and save event data, noting which bus A nodes are offline and whether related line-voltage codes are present.
- Inspect the negative conductor and connectors for a short to a power wire, chafing, water entry, or damaged terminals.
- Check system voltage and affected module power and grounds before interpreting bus-line readings.
- Measure the negative line under the manufacturer's specified conditions and test for a short to power against the manufacturer's specification.
- If the wiring passes, isolate bus A modules and gateway connections using the manufacturer's procedure to identify a transceiver or routing fault.
Common fixes
- Repair a bus A negative wire shorted to battery or another power feed.
- Repair damaged wiring or terminals on the negative conductor.
- Correct a verified module power or ground problem.
- Replace a faulty transceiver or repair gateway routing only after isolation tests confirm the source.
Can I keep driving?
This fault can take bus A modules offline or put affected systems into limp mode. Avoid driving if steering, braking, powertrain control, or other essential functions are impaired, and recover the vehicle if it is not safe to operate.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.