P0800 code meaning
Transfer Case Control System (MIL Request)
Powertrain system Generic code P08xx codes Check engine light
What P0800 means
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.
P0800 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor0.5 to 4 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P0800
- Check engine lamp on
- 'Service 4WD' or similar warning
- All-wheel drive or low range cannot be selected
Common causes of P0800
- Most 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
- Less likelyTransfer case module faulty
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transfer case control moduleEngine control moduleTransfer case wiring
What each part of P0800 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 8 | Area: transmission. |
| 00 | The exact fault in that area. |
What to do next
- Note P0800 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P0800
What does P0800 mean?
P0800 means "Transfer Case Control System (MIL Request)". 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. It is a generic code, so it means the same on every make.
Is it safe to drive with P0800?
Drive gently and only to a workshop. With P0800 the car can go into limp mode (reduced power) to protect itself.
Will P0800 fail an emissions test?
Yes, it can. P0800 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P0800 to fix?
Difficulty: medium. A typical repair takes 0.5 to 4 hours of work. This is a job for a workshop.
Will P0800 clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.