U0038 code meaning
Vehicle Communication Bus B Performance
What U0038 means
U0038 flags Vehicle Communication Bus B as present but unreliable: frames arrive late, incompletely or for a while not at all, rather than the bus being dead outright. Volkswagen's 2014 Touareg data book describes the trigger as a global time-out in which no messages come in any longer. Honda uses U0038 for the TM-CAN link between transmission and engine control: on 2016-17 Civic CVT models it appeared together with U0101 when an internal TCM fault cut the link, leaving the car stuck in Park without cranking and with several warning lamps lit. Honda replaces the TCM and on 2016 cars also updates the PCM software. Compared with U0037 the code describes a bus that still exists but whose traffic breaks off, so intermittent contacts, a failing node or software are the usual suspects.
U0038 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modePossible
- Repair difficultyHard
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0038
- Selector stuck in Park, engine does not crank (Honda Civic CVT)
- Several warning lamps on at once
- Functions drop out intermittently
Common causes of U0038
- Most likelyInternal fault in a module on Bus B (Honda Civic: transmission control module)
- PossibleLoose or corroded terminals interrupting traffic now and then
- PossibleSoftware mismatch between modules on the bus
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Bus b wiringControl module
What each part of U0038 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 38 | The exact fault in that area. |
What to do next
- Note U0038 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 U0038
What does U0038 mean?
U0038 means "Vehicle Communication Bus B Performance". U0038 flags Vehicle Communication Bus B as present but unreliable: frames arrive late, incompletely or for a while not at all, rather than the bus being dead outright. It is a generic code, so it means the same on every make.
Is it safe to drive with U0038?
Drive gently and only to a workshop. With U0038 the car can go into limp mode (reduced power) to protect itself.
Will U0038 fail an emissions test?
U0038 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 U0038 to fix?
Difficulty: hard. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will U0038 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.