U0066
Vehicle Communication Bus E (+) Open
Communication network (CAN bus)
Generic OBD-II
Medium
What it means
U0066 means the CAN-high (positive) wire of communication Bus E has an open circuit — a break or disconnection that stops modules on that bus from communicating. It usually shows up as warning lights and one or more modules going offline. Which features are affected depends on what "Bus E" carries on your specific vehicle.
Medium
Can I keep driving? Usually drivable, but an open bus wire can cut several modules off from the network — expect warning lights and lost features until it's repaired.
Common symptoms
What you'll notice
- Warning lights on and several features not working
- Modules on Bus E unreachable with a scan tool
- A specific system or module going completely offline
- Intermittent operation if the open is a loose or broken wire
Common causes
Most likely first
- Broken or disconnected CAN-high (+) wire on Bus ELikely
- Corroded, backed-out, or loose connector pin on the busCommon
- Damaged harness from chafing, a repair, or rodent chewCommon
- Failed splice or terminal in the bus wiringLess often
- A module with an internal open on its bus connectionLess often
How to diagnose & fix
Work through it in order
- Scan all modules and note which are unreachable to bracket where the open is on Bus E.
- Inspect the CAN-high wiring and connectors for breaks, corrosion, or backed-out pins.
- Perform a continuity/voltage-drop test along the CAN-high line to locate the open.
- Check connector terminals for spread pins or poor tension at each module on the bus.
- Repair the broken wire, splice, or terminal, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0066?+
Often yes for short trips, but an open bus wire can disable systems you depend on, so have it diagnosed before extended driving.
Can I just clear U0066?+
No lasting effect — an open circuit is a hard fault that returns until the broken wire or connection is repaired.
Related codes
Often seen with U0066
Read & clear U0066 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