U0009

High Speed CAN Communication Bus (-) shorted to Bus (+)

Q: Is it safe to drive with U0009?

Often not. A shorted CAN bus can disable systems needed to run and to brake or steer safely, so if the car won't start or runs erratically, have it towed and diagnosed.

Q: Can I just clear U0009?

No. A shorted bus is a hard wiring fault — clearing does nothing until the short between the CAN wires (or the failed module) is found and repaired.

Communication network (CAN bus) Generic OBD-II High

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.

High

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.

Real-world scan data

Seen in

scans in the past year

Found in

<0.1%

of scans

<0.1%

of scans that found faults

Figures reflect only diagnostic scans recorded through our own apps and tools. Cars are typically scanned because a symptom or warning light prompted it, so these counts describe our scan records — not the incidence of faults in any model, and not the quality, reliability, or safety of any vehicle. No comparison between manufacturers or models is implied. All trademarks belong to their respective owners; no affiliation or endorsement is implied.

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?+

Often not. A shorted CAN bus can disable systems needed to run and to brake or steer safely, so if the car won't start or runs erratically, have it towed and diagnosed.

Can I just clear U0009?+

No. A shorted bus is a hard wiring fault — clearing does nothing until the short between the CAN wires (or the failed module) is found and repaired.

Read & clear U0009 yourself

Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.

▶ Get it on Google Play

✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX