U1017: Loss of Serial Communications for Class 2 Devices (GM)
Severity: medium
What it means: On older GM vehicles, a control module has stopped talking on the Class 2 data network (the wiring the car's computers use to share information). It doesn't name a specific part. A shop has to find which module dropped off the network.
Safe to drive? Depends on which module is affected. If warning lights, gauges or the engine act up, get it checked soon.
Common symptoms
- Several warning lights or random electrical problems
- Gauges or features not working
- Multiple communication codes stored at once
Likely causes, ranked
- Water or corrosion in wiring or connectorsShop
- Blown fuse or bad power or ground to a moduleDIY
- Failed control moduleShop
Vehicle-specific notes
- 2006–2010 Hummer H3: A Hummer Forums owner with water on both floors of a 2010 H3 had B0790, B2725 and U1017 stored together, plus corrosion on wiring. Members blamed clogged sunroof drains. Read the full answer · Source
What it means: On older GM vehicles, a control module has stopped talking on the Class 2 data network (the wiring the car's computers use to share information). It doesn't name a specific part. A shop has to find which module dropped off the network.
Severity: Medium. Safe to drive? Depends on which module is affected. If warning lights, gauges or the engine act up, get it checked soon.
DIY or shop?
Checking fuses and looking for water damage is DIY. Network diagnosis is a shop job.
Before you replace parts
- Read all stored codes and freeze-frame data, not just this one.
- Check your VIN for recalls, service bulletins and extended coverage.
- Inspect wiring and connectors for the related sensor or part before buying parts.
- Clear the code only after a repair, then confirm it stays off.
Safety / mechanic note
Verify with a mechanic. Communication faults can affect safety systems depending on which module dropped out. A code points to a circuit or system, not always a specific part.