U0020Low Speed CAN Communication Bus Performance
- Generic OBD-II code · Network
- How the car detects it
- U0020 reports a low-speed CAN that still runs but delivers its traffic unreliably. GM documents it for the 2011 Saab 9-5, whose low-speed GMLAN is a single wire: a module sets U0020 when a monitored cyclic message, which doubles as proof that the sender is available, fails to arrive, and then substitutes a default value. Saab adds that some modules store it when the bus wakes up or the supply returns before they have learned which partners are present; diagnosis follows the symptoms or the U0100-U02FF codes. GM told technicians to ignore a current U0020 in the video processing module of 2019 Silverado/Sierra trucks as a software artefact, and lists it for 2017 trucks whose gateway module hangs until its fuse is pulled. Unlike U0019 the bus itself is usually intact.
- What you may notice
- Often no noticeable symptom, code found during a scan
- Sporadic dropouts of comfort or display functions
- Several modules store communication codes at the same time
- Likely causes
- PossibleCode stored while modules wake up or after the supply was interrupted
- PossibleSoftware anomaly in one module (GM video processing module 2019)
- PossibleGateway module stops communicating or has loose terminals
- RareIntermittent contact in the low-speed bus wiring
- Repair
- Medium · Usually a job for a workshop.Typical cost: €0 – €400
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.