U0018
Medium Speed CAN Communication Bus (-) shorted to Bus (+)
Vehicle communication network
Generic OBD-II
Medium
What it means
U0018 means the medium-speed CAN bus has its negative wire shorted to the positive wire, which corrupts communication across that bus. Any modules sharing the bus can drop offline, triggering warning lights and disabled features. It is a physical wiring fault — usually a chafed harness, a wet connector, or a failed module pulling the bus down.
Medium
Can I keep driving? Often still driveable, but expect several warning lights and dead features, and if this bus carries engine or brake modules you may get limp mode — diagnose promptly.
Common symptoms
What you'll notice
- Several warning lights on at once (ABS, traction, airbag, etc.)
- Multiple modules or features not working, varying by vehicle
- Modules show 'no response' or communication errors when scanned
- Erratic gauge or accessory behavior
Common causes
Most likely first
- Chafed or pinched bus wiring shorting CAN- to CAN+Likely
- Water or corrosion in a connector bridging the two bus wiresCommon
- A failed module dragging the whole bus downCommon
- Bus wiring damaged after a collision or prior repair workLess often
How to diagnose & fix
Work through it in order
- Scan every module and record all stored U-codes to map which bus and modules are affected.
- Inspect the medium-speed CAN wiring for chafing, pinch points, and water intrusion.
- Measure resistance/voltage between CAN+ and CAN- to confirm the short.
- Disconnect suspect modules one at a time to isolate a shorted module.
- Repair the wiring or connector, or replace the faulty module, then clear and retest.
FAQ
Quick answers
Is it safe to drive with U0018?+
It depends which modules are on this bus. Many vehicles put body and comfort systems on the medium-speed bus and stay driveable, but a bus short can cause erratic electrical behavior, so get it checked promptly.
Can I just clear U0018?+
It will come back until the short is repaired. A shorted bus is a physical wiring fault, not something clearing can fix.
Related codes
Often seen with U0018
Read & clear U0018 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