High Speed CAN Communication Bus (+) Open
What it means
U0003 means the module detected an open circuit on the high-speed CAN (+) wire — the backbone that lets powertrain and chassis modules talk to each other. An open here can drop multiple modules off the bus, so it often brings a cluster of warning lights, other 'lost communication' codes, and sometimes a no-start or limp mode. It's an electrical fault: find and repair the broken wire, connector, or failed module.
Can I keep driving? Often no — an open on the high-speed CAN (+) wire can knock modules off the bus, causing multiple warning lights, limp mode, or a no-start; have it diagnosed before driving.
Common symptoms
What you'll notice
- Multiple warning lights (check-engine, ABS, traction, airbag, etc.) at once
- Several other 'lost communication' (U-series) codes stored
- No-start, stall, or reduced-power/limp mode
- Gauges, dash, or accessories behaving erratically or going dead
Common causes
Most likely first
- Open or broken CAN high (+) bus wire between modulesLikely
- Corroded, loose, or backed-out pin at a module or inline connectorCommon
- A failed module that has opened or is dragging down the busCommon
- Damaged bus wiring from a repair, rodent, or physical harmLess often
- Faulty terminating resistor or bus spliceLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record every stored U-code — the pattern of which modules dropped off helps locate the open.
- Inspect the CAN (+) wiring and connectors along the bus for breaks, corrosion, or backed-out pins.
- With the key off, measure CAN bus resistance and continuity to find the open segment; check terminating resistors.
- Disconnect suspect modules one at a time to see if the bus recovers, isolating a failed module.
- Repair the open wire or connector, then clear the codes and confirm all modules communicate.
FAQ
Quick answers
Is it safe to drive with U0003?+
Can I just clear U0003?+
Related codes
Often seen with U0003
Read & clear U0003 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.