Vehicle Communication Bus B (-) Low
What it means
U0043 means the voltage on the CAN "low" (-) wire of vehicle communication Bus B has dropped below its expected range, so modules on that bus struggle to exchange data. It usually points to a wiring short-to-ground, a bad connector, or a module dragging the bus down. The car often still drives, but if drivetrain modules share this bus you can see limp mode, so it's worth tracing quickly.
Can I keep driving? Often yes, but not guaranteed — a low CAN voltage garbles data on this bus; if the affected network carries drivetrain modules you could see limp mode, so have it traced promptly.
Common symptoms
What you'll notice
- Warning lights on and several modules reporting communication faults
- Features on Bus B become intermittent or stop working
- Gauge, display, or accessory glitches
- Reduced power or limp mode if the affected bus carries powertrain modules
Common causes
Most likely first
- CAN-low (-) wire shorted to ground or pulled below its normal rangeLikely
- Chafed, pinched, or corroded bus wiring or a bad connectorCommon
- A failing module dragging the bus voltage downCommon
- Poor power or ground feed to a networked moduleLess often
- Water intrusion in a connector or moduleLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record every stored code to map which part of Bus B is affected.
- Inspect the Bus B wiring and connectors for chafing, corrosion, or moisture.
- Measure CAN-high/low voltage and resistance against spec to locate the short-to-low.
- Disconnect suspect modules one at a time to find one pulling the bus down.
- Repair the wiring or replace the faulty module, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0043?+
Can I just clear U0043?+
Related codes
Often seen with U0043
Read & clear U0043 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.