B2725: Transfer Case Mode Switch Circuit Malfunction (GM)
Severity: medium
What it means: On GM trucks such as the Hummer H3, the transfer case control module sees an invalid signal from the dash-mounted 4WD mode switch. It can stop the 4WD system from shifting and turn on the Service 4WD light.
Safe to drive? Usually yes on dry roads, but four-wheel-drive may not shift or work. Get it checked before you need 4WD.
Common symptoms
- Service 4WD light on
- 4WD will not shift between modes
- 4WD mode lights not responding
Likely causes, ranked
- Faulty 4WD mode switchShop
- Wet, damaged or corroded switch wiringShop
- Failed transfer case 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 GM trucks such as the Hummer H3, the transfer case control module sees an invalid signal from the dash-mounted 4WD mode switch. It can stop the 4WD system from shifting and turn on the Service 4WD light.
Severity: Medium. Safe to drive? Usually yes on dry roads, but four-wheel-drive may not shift or work. Get it checked before you need 4WD.
DIY or shop?
Checking for water and cleaning connectors is DIY. Testing the switch and circuits 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. Do not count on 4WD working until this is fixed. A code points to a circuit or system, not always a specific part.