U009A code meaning
Vehicle Communication Bus H (-) Shorted to Bus H (+)
What U009A means
U009A means the two wires of Vehicle Communication Bus H touch each other, on a CAN CAN-Low against CAN-High. No manufacturer documentation of U009A is public. On a high-speed CAN this ends all traffic; onsemi's bench node could not send and drew about 47 mA against roughly 65 mA on a healthy bus. A fault-tolerant low-speed CAN can live with it: the TJA1055 from NXP initially reads the bus as constantly dominant, and only once a time-out has run does it disable its CANL driver and carry on single-wire, returning to differential operation once the wires are separated. So on some cars U009A comes with a dead network, on others only with a stored code. Separating harness sections while measuring resistance between the wires narrows down the spot.
U009A 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 U009A
- On high-speed CAN: complete loss of Bus H functions
- Lost-communication codes for several modules
Common causes of U009A
- Most likelyBus wires crushed together
- PossibleWet or corroded splice joining both wires
- Less likelyInternal short in a module's transceiver
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus h wiringModule connector
What each part of U009A means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 9A | The exact fault in that area. |
What to do next
- Note U009A 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 U009A
What does U009A mean?
U009A means "Vehicle Communication Bus H (-) Shorted to Bus H (+)". U009A means the two wires of Vehicle Communication Bus H touch each other, on a CAN CAN-Low against CAN-High. It is a generic code, so it means the same on every make.
Is it safe to drive with U009A?
Drive gently and only to a workshop. With U009A the car can go into limp mode (reduced power) to protect itself.
Will U009A fail an emissions test?
U009A 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 U009A to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U009A clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.