Powertrain, generic · Transmission

P0800 Transfer Case Control System (MIL Request)

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Fault in the transfer case system stored in its module (shift motor, sensor, clutch)
Wiring or connector at the transfer case (terminal tension, corrosion)
Transfer case module software
Transfer case module faulty

Symptoms

  • Check engine lamp on
  • 'Service 4WD' or similar warning
  • All-wheel drive or low range cannot be selected

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€80–1,500
Time0.5–4 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

transfer case control moduleengine control moduletransfer case wiring

Related codes

P0700P0802U0102P0650

References: law.cornell.edu, static.nhtsa.gov, gsi.ext.gm.com.