P0800Transfer Case Control System (MIL Request)
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P0800 works like P0700 for the transmission: the transfer case control module has detected a fault of its own that it rates as emissions-relevant and asks the engine control module to turn on the MIL. The engine module only stores P0800; the actual fault – often C, U or manufacturer codes – sits in the transfer case module and needs a scan tool that addresses it. CARB requires monitoring of an electronic transfer case only where it feeds other diagnostics, for example the 4WD-low signal that GM uses as an enable condition; this is why most transfer case modules never request the MIL and P0800 hardly appears in manufacturer documents. A GM bulletin for 2020–23 trucks with 'Service 4WD' and the MIL points to wiring and terminal contact at the transfer case.
- What you may notice
- Check engine lamp on
- 'Service 4WD' or similar warning
- All-wheel drive or low range cannot be selected
- Likely causes
- LikelyFault in the transfer case system stored in its module (shift motor, sensor, clutch)
- PossibleWiring or connector at the transfer case (terminal tension, corrosion)
- PossibleTransfer case module software
- RareTransfer case module faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €80 – €1,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.