C0327: Transfer Case Encoder Circuit Malfunction (GM)
Severity: medium
What it means: On GM 4WD trucks and SUVs like the Hummer H3, the transfer case control module reads the position of the encoder motor (the electric motor that shifts the transfer case between 2WD, 4-High and 4-Low). C0327 means the module got a signal from the encoder that doesn't make sense. When it sets, the module stops the motor, turns on Service 4WD and turns off the 4WD indicators.
Safe to drive? Usually drivable in 2WD, but 4WD may not work. Don't count on 4-Low or 4WD in snow or off-road until it's fixed.
Common symptoms
- Service 4WD message
- 4WD button lights flashing or off
- 4WD or 4-Low not engaging, or clicking in and back out
Likely causes, ranked
- Water or dirt inside the encoder motorShop
- Corroded or damaged encoder wiring or plugDIY or shop
- Binding shift parts in the transfer caseShop
- Transfer case control module faultShop
Vehicle-specific notes
- 2006–2010 Hummer H3: GM bulletin 09-04-21-005 covers Service 4WD with C0327 on the 2006–2010 H3 and H3T: a revised encoder motor, a new seal and a transfer case module update. Owners on Hummer forums clean the motor's plug first and warn that rebuilt or off-brand motors often fail. Read the full answer · Source
What it means: On GM 4WD trucks and SUVs like the Hummer H3, the transfer case control module reads the position of the encoder motor (the electric motor that shifts the transfer case between 2WD, 4-High and 4-Low). C0327 means the module got a signal from the encoder that doesn't make sense. When it sets, the module stops the motor, turns on Service 4WD and turns off the 4WD indicators.
Severity: Medium. Safe to drive? Usually drivable in 2WD, but 4WD may not work. Don't count on 4-Low or 4WD in snow or off-road until it's fixed.
DIY or shop?
DIY for cleaning the encoder plug and checking wiring. The GM fix includes a module update that needs dealer-level software.
Before you replace parts
- Read all chassis codes with a scanner that can talk to the transfer case module.
- Inspect and clean the encoder motor plug and wiring under the truck.
- Check your VIN for GM bulletins on the encoder motor.
- If replacing the motor, use a genuine part and have the module updated.
Safety / mechanic note
Verify with a mechanic. Without working 4WD you may lose traction in snow, mud or on steep ground. A code points to a circuit or system, not always a specific part.