NQH is the RPO code for GM’s two-speed electronic Autotrac transfer case — the one with the rotary dial rather than a floor lever, and the one that adds an automatic four-wheel-drive mode on top of 2HI, 4HI and 4LO.
It is worth knowing you have it for two reasons: it changes how you are supposed to use four-wheel drive, and it is the transfer case behind one of GM’s own published service bulletins.
Where NQH is documented
| Year | How GM described it | Source |
|---|---|---|
| 2010–2013 | “Electronically controlled transfer case” in the listed four-wheel-drive vehicles | GM bulletin PIP5003C: Intermittent Service 4WD Message, hosted by NHTSA |
| 2021 | “Transfer case, two-speed electronic Autotrac with rotary dial control (4WD only)” | GM Upfitter special-service specification guides |
| 2022–2023 | “Transfer case, two-speed — electronic Autotrac with rotary dial control, 4WD models only” | GM Upfitter specification guides |
| 2025–2026 | “Transfer case, two-speed electronic AutoTrac” | GM Fleet order guides; 2026 Silverado 9C1 spec guide; GM Canada eOGLD |
Thirty-four GM-sourced records. The GMT900-era entry comes from a service bulletin rather than an order guide, which is unusual and useful — it means GM itself named the code while describing a fault.
Autotrac is not the same as part-time 4WD
| Position | What it does | Use it |
|---|---|---|
| 2HI | Rear wheels only | Dry pavement, always |
| AUTO / 4 AUTO | Rear-biased, engages the front automatically when the rear slips | Mixed or unpredictable surfaces — and it is safe on dry pavement |
| 4HI | Front and rear locked together | Snow, gravel, loose surfaces only |
| 4LO | Locked, with low-range reduction | Crawling, launching a boat, deep snow |
AUTO is the mode that justifies the code. A part-time case has no equivalent — leave a part-time truck in 4HI on dry pavement and you bind the driveline. With NQH you have a setting that handles the in-between conditions without that risk.
“Service 4WD” on an NQH truck
GM’s PIP5003C covers an intermittent “Service 4WD” message on 2010–2013 trucks with the electronic transfer case. If that message is what brought you here, work the problem in the right order rather than buying a control module first:
- The encoder motor on the transfer case is the most common failure, and it fails by wearing its position sensor.
- The transfer case control module and its connectors are next.
- Selector switch and wiring faults account for a fair share of intermittent cases.
Our full diagnosis order is in Chevy 4WD not engaging: Service 4WD light, encoder motor and TCCM diagnosis.
Separately, on 1998–2007 GM 4x4s there is a mechanical problem worth knowing about regardless of which transfer case you have — the internal oil pump wears through the magnesium case from the inside. The fix is cheap and the failure is not: GM transfer case pump rub.
How to check what you have
- Look at the selector. A rotary dial with an AUTO position points to NQH. A floor-mounted lever does not.
- Decode NQH for your model year and run the whole label — the transfer case code, the differential and the axle ratio together describe the drivetrain.
- Check the tag on the transfer case itself if the truck has been apart. The label records the build, not the current hardware.
What NQH does not tell you
- It is not an off-road package. That is Z71.
- It is not a locking differential. That is G80. AUTO mode manages front-to-rear, not side-to-side.
- It is not skid plates. Those are NZZ.
Sources
- PIP5003C: Intermittent Service 4WD Message, GM manufacturer communication hosted by NHTSA
- 2021–2023 GM Upfitter police and special-service package specification guides
- 2026 Silverado 9C1 Police Package Specification Guide, GM Fleet
- 2025–2026 GM Fleet order guides; GM Canada eOGLD order guide
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