U0091 code meaning
Vehicle Communication Bus G (-) Shorted to Bus G (+)
What U0091 means
U0091 closes the Bus G block: the (-) and (+) wires of Vehicle Communication Bus G are joined, on a CAN CAN-Low to CAN-High. No manufacturer has published a use of U0091. With both wires bridged no voltage difference can form, so a high-speed CAN carries no frames at all. Transceiver self-diagnosis is of little help here; NXP notes that its TJA1043 reports shorts to ground and supply but not a short between the two bus wires, so the module concludes the fault from the silence. Measuring is quick: Nissan gives about 60 ohms between the wires as normal and lists zero ohms for a short between them. To find the spot, unplug modules and harness sections one at a time until the reading returns to normal.
U0091 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 U0091
- Complete loss of the functions served by Bus G
- Scan tool cannot reach any module on Bus G
Common causes of U0091
- Most likelyBus wires crushed together, e.g. under a seat rail or panel
- PossibleCorroded or wet splice bridging both wires
- Less likelyInternal short in one 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 g wiringModule connector
What each part of U0091 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 91 | The exact fault in that area. |
What to do next
- Note U0091 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 U0091
What does U0091 mean?
U0091 means "Vehicle Communication Bus G (-) Shorted to Bus G (+)". U0091 closes the Bus G block: the (-) and (+) wires of Vehicle Communication Bus G are joined, on a CAN CAN-Low to CAN-High. It is a generic code, so it means the same on every make.
Is it safe to drive with U0091?
Drive gently and only to a workshop. With U0091 the car can go into limp mode (reduced power) to protect itself.
Will U0091 fail an emissions test?
U0091 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 U0091 to fix?
Difficulty: hard. A typical repair takes 1 to 6 hours of work. This is a job for a workshop.
Will U0091 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.