U0090 code meaning
Vehicle Communication Bus G (-) High
What U0090 means
U0090 is logged when Bus G's (-) wire is pulled up, typically by a short to a supply feed; in CAN terms this is the CAN-Low line. U0090 is not described in any public manufacturer source. Unlike a grounded CAN-Low, this fault normally stops the bus: onsemi found transmission impossible with CAN-Low at 12 V, and NXP rates it as a short under which communication fails. The search is easier once you know which feed is involved. Nissan's CAN diagnostic chart measures each bus wire to ground both with the key off and with it on, and keeps separate entries for shorts to battery and to an ignition feed. A fault that is present only with the ignition on points to a switched circuit, one that persists with the key off to a permanent battery feed.
U0090 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 5 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0090
- All modules on Bus G stop responding at once
- Warning lamps and lost-communication codes in several systems
- Fault may come and go with the ignition switch position
Common causes of U0090
- Most likely(-) wire shorted to a permanent battery feed
- Possible(-) wire touching a switched ignition feed in the harness
- Less likelyRetrofitted equipment spliced into the bus wires
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus g wiringCAN low wire
What each part of U0090 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 90 | The exact fault in that area. |
What to do next
- Note U0090 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 U0090
What does U0090 mean?
U0090 means "Vehicle Communication Bus G (-) High". U0090 is logged when Bus G's (-) wire is pulled up, typically by a short to a supply feed; in CAN terms this is the CAN-Low line. It is a generic code, so it means the same on every make.
Is it safe to drive with U0090?
Drive gently and only to a workshop. With U0090 the car can go into limp mode (reduced power) to protect itself.
Will U0090 fail an emissions test?
U0090 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 U0090 to fix?
Difficulty: hard. A typical repair takes 1 to 5 hours of work. This is a job for a workshop.
Will U0090 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.