U0020 code meaning
Low Speed CAN Communication Bus Performance
What U0020 means
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.
U0020 at a glance
- Check engine lightUsually not
- Emissions testNot an emissions code
- Limp modeNot expected
- Repair difficultyMedium
- Typical labor0.3 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of U0020
- 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
Common causes of U0020
- 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
- Less likelyIntermittent contact in the low-speed bus wiring
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Low speed CAN wiringBody control moduleControl module
What each part of U0020 means
| U | Network system: communication between the control modules (CAN bus). |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 20 | The exact fault in that area. |
What to do next
- Note U0020 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about U0020
What does U0020 mean?
U0020 means "Low Speed CAN Communication Bus Performance". U0020 reports a low-speed CAN that still runs but delivers its traffic unreliably. It is a generic code, so it means the same on every make.
Is it safe to drive with U0020?
U0020 does not normally turn on the check engine light by itself. Watch for the symptoms above and have it checked soon.
Will U0020 fail an emissions test?
U0020 is not an emissions code, so on its own it usually does not fail an emissions test. Other stored codes or a lit check engine light still can.
How hard is U0020 to fix?
Difficulty: medium. A typical repair takes 0.3 to 3 hours of work. This is a job for a workshop.
Will U0020 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.