U0049
Vehicle Communication Bus C (+) Low
Communication network (vehicle bus)
Generic OBD-II
Medium
What it means
U0049 means the plus (+) side of vehicle communication bus "C" is reading lower than it should — usually a short to ground or a module dragging the line down. When the bus voltage is pulled low, modules on that bus can't communicate properly and go offline. The impact depends on which modules share bus C; the fault is typically a shorted or chafed wire, a corroded connector, or a failed module.
Medium
Can I keep driving? Depends on what shares bus C — the car may drive normally or may lose features and light warnings; if a powertrain module is on this bus you could see limp mode.
Common symptoms
What you'll notice
- Warning lights on with multiple lost-communication codes
- One or more modules unresponsive to a scan tool
- Features handled by bus-C modules stop working
- Cluster warnings or gauges affected
Common causes
Most likely first
- (+) bus wire shorted to ground or pulled lowLikely
- Chafed harness grounding the bus lineCommon
- Corroded or damaged connector dragging the signal lowCommon
- A failed module loading down the busLess often
How to diagnose & fix
Work through it in order
- Scan all modules to see which ones dropped off bus C.
- Check the (+) bus wire for a short to ground and inspect the harness for chafing.
- Disconnect suspect modules one at a time to find one loading the bus low.
- Repair the short or replace the faulty module.
- Clear codes and confirm normal communication.
FAQ
Quick answers
Is it safe to drive with U0049?+
Only if drivability and safety systems are unaffected. A bus pulled low can take modules offline, so diagnose it to know what's lost before relying on the car.
Can I just clear U0049?+
A shorted or low bus line won't fix itself — the code returns until the wiring short or failed module is repaired.
Related codes
Often seen with U0049
Read & clear U0049 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