U0038
Vehicle Communication Bus B Performance
Vehicle communication network
Generic OBD-II
Medium
What it means
U0038 means communication on the vehicle's Bus B is degraded or intermittent rather than fully lost — messages are getting through unreliably. Modules on that bus may drop in and out, causing warning lights and features that work erratically. The usual cause is partially damaged wiring, a loose or corroded connector, or a module that is loading the network.
Medium
Can I keep driving? Usually driveable, but communication on this bus is degraded, so modules may drop in and out with warning lights and intermittent features — diagnose before symptoms worsen.
Common symptoms
What you'll notice
- Intermittent warning lights that come and go
- Features on this bus working erratically
- Modules occasionally unresponsive when scanned
- Glitchy gauges or accessories
Common causes
Most likely first
- Chafed or partially damaged bus wiringLikely
- Corroded or loose connector causing intermittent contactCommon
- A weak or failing module loading the busCommon
- Poor power or ground causing dropoutsLess often
How to diagnose & fix
Work through it in order
- Scan all modules and record U-codes to identify the affected bus and modules.
- Wiggle-test the Bus B wiring and connectors while watching data to catch the dropout.
- Inspect for corrosion, chafing, and loose terminals.
- Check module power and grounds.
- Repair the wiring or replace the failing module, clear codes, and retest.
FAQ
Quick answers
Is it safe to drive with U0038?+
A 'Performance' fault means communication is degraded rather than fully lost, so the car is often driveable, but which systems are affected depends on the bus layout. If safety systems drop out, get it fixed promptly.
Can I just clear U0038?+
Intermittent bus faults return until the loose or damaged connection is found and repaired. Clearing only masks it temporarily.
Related codes
Often seen with U0038
Read & clear U0038 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX