U0020
Low Speed CAN Communication Bus Performance
Network / communication
Generic OBD-II
Medium
What it means
U0020 means the low-speed CAN network — the bus that ties together convenience and comfort modules like locks, lighting, audio, and climate control — isn't performing to spec. Communication is degraded or unreliable, usually from wiring damage, a poor connector, or one module disrupting bus traffic. The engine normally keeps running, but expect warning lights and features that come and go.
Medium
Can I keep driving? Usually yes — the low-speed bus handles convenience and comfort modules rather than the engine, so the car drives but some features and warning systems may misbehave.
Common symptoms
What you'll notice
- Warning lights on with no obvious single failure
- Convenience features glitchy — locks, windows, lighting, audio, or HVAC
- Modules slow to respond or dropping off the scan tool
- Intermittent faults that change with temperature or vibration
Common causes
Most likely first
- Corroded, chafed, or broken low-speed CAN wiringLikely
- Poor connector contact or water intrusion at a moduleCommon
- A single failing module degrading bus trafficCommon
- Failed terminating resistor on the busLess often
- Software or configuration mismatch after a module or battery serviceLess often
How to diagnose & fix
Work through it in order
- Scan every module and record which report bus performance faults or drop off; the shared segment points to the problem area.
- Inspect low-speed CAN wiring and connectors for corrosion, chafing, and water, especially in doors and kick panels.
- Measure bus voltage and resistance against spec to confirm an open, short, or bad resistor.
- Isolate a chatty or dead module by disconnecting suspects one at a time.
- Repair the wiring or replace the failing module, then clear and re-test.
FAQ
Quick answers
Is it safe to drive with U0020?+
Generally yes — the low-speed bus carries comfort and convenience systems, not the engine, but some features and alerts may not work, so get it diagnosed soon.
Can I just clear U0020?+
Clearing hides it briefly, but it comes back until the bus wiring or failing module is repaired.
Related codes
Often seen with U0020
Read & clear U0020 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