High Speed CAN Communication Bus (-) shorted to Bus (+)
What it means
U0009 means the high-speed CAN network's negative (CAN-low) wire is shorted to the positive (CAN-high) wire. CAN is the shared bus that lets the car's control modules talk to each other, so a short can take several modules offline at once — often producing no-start, stalling, limp mode, and a cluster of warning lights. It's a wiring or module fault that needs proper bus diagnosis, not just clearing.
Can I keep driving? Often no — a shorted CAN bus can knock multiple modules offline, causing no-start, stalling, or limp mode with many warning lights; have it towed if it won't run.
Common symptoms
What you'll notice
- Multiple warning lights on at once (ABS, airbag, traction, check-engine)
- No-start, stalling, or limp mode
- Dead or erratic gauges and warning messages
- Several modules showing lost-communication (U-series) codes
Common causes
Most likely first
- High-speed CAN bus wires (CAN-high and CAN-low) shorted togetherLikely
- Chafed, pinched, or water-damaged harness bridging the two bus wiresCommon
- Corroded or damaged connector shorting the bus pairCommon
- A failed module internally shorting the bus linesLess often
- Wiring damage from a prior repair or rodent damageLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record every U-code to map which are still communicating.
- Inspect the CAN harness and connectors for chafing, pinching, corrosion, or water intrusion.
- Measure resistance between CAN-high and CAN-low with the key off to find the short (should not read near zero).
- Disconnect modules one at a time to isolate whether a module or the wiring is shorting the bus.
- Repair the shorted wiring or replace the faulty module, then clear codes and re-scan all modules.
FAQ
Quick answers
Is it safe to drive with U0009?+
Can I just clear U0009?+
Related codes
Often seen with U0009
Read & clear U0009 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.