U0023Low Speed CAN Communication Bus (+) High
- Generic OBD-II code · Network
- How the car detects it
- U0023 means CAN-High, the (+) conductor of a dual-line low-speed CAN, sits too high, typically shorted to battery voltage or a 5 V supply. Under ISO 11898-3 this pins the line at a level the receivers read as permanently dominant. NXP's TJA1055 handles it as failure 3 or 3a in two steps: once an initial delay expires it falls back to single-wire operation, and if the line is still too high it moves over to CAN-Low, switches its CAN-High driver off and weakens that line's termination; detection takes about 1.6 to 8 ms. Traffic continues on one wire, though electromagnetic robustness is worse in that mode. No manufacturer documents U0023 publicly; GM's low-speed GMLAN, being a single conductor, offers no (+)/(-) pair. CAN-High measuring near battery voltage against ground instead of its resting level close to 0 V points to the short.
- What you may notice
- Comfort functions mostly still work, occasional glitches
- Increased sensitivity to interference, e.g. with radio transmitters nearby
- Code stored in several body modules
- Likely causes
- LikelyCAN-High chafed against a battery feed or ignition wire
- PossibleWater in a connector bridging CAN-High to a supply pin
- RareRetrofitted accessory tapped into the wrong wire
- Repair
- Medium · Usually a job for a workshop.Typical cost: €50 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.