U0009 code meaning
High Speed CAN Communication Bus (-) Shorted to Bus (+)
What U0009 means
U0009 describes CAN-Low and CAN-High of the high-speed bus being shorted to each other. The voltage difference between them then stays at zero, which every receiver interprets as recessive, so a dominant bit can never form; onsemi's tests show transmission stopping entirely and controllers running into bus-off. According to NXP, transceiver bus diagnosis cannot detect this short, so a module infers it from protocol errors instead. No manufacturer documents U0009 publicly. With the battery disconnected, the resistance between both lines reads close to zero ohms instead of the usual 60. Likely sources are a crushed harness section, water inside a splice or connector, or a damaged transceiver in one module bridging its two bus pins. Unplugging modules one by one narrows the location down.
U0009 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 6 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0009
- No communication on the high-speed network at all
- Numerous warnings, fallback modes, possibly no start
- Scan tool reaches only modules on other networks
Common causes of U0009
- Most likelyBus pair crushed so that both conductors touch
- PossibleWater or corrosion bridging CAN-High and CAN-Low in a splice or connector
- Less likelyFailed transceiver shorting both bus pins inside a module
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
CAN high wireCAN low wireModule connector
What each part of U0009 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 09 | The exact fault in that area. |
What to do next
- Note U0009 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0009
What does U0009 mean?
U0009 means "High Speed CAN Communication Bus (-) Shorted to Bus (+)". U0009 describes CAN-Low and CAN-High of the high-speed bus being shorted to each other. It is a generic code, so it means the same on every make.
Is it safe to drive with U0009?
Drive gently and only to a workshop. With U0009 the car can go into limp mode (reduced power) to protect itself.
Will U0009 fail an emissions test?
U0009 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0009 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U0009 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.