P279A code meaning
Transfer Case Gear High Incorrect Ratio
Powertrain system Generic code P27xx codes Check engine light
What P279A means
P279A fires when the transfer case should be in its high range, but the measured ratio says otherwise. GM explains the check in its 2019 ECM tables (section for the LCV engine): the ratio is calculated from transmission output speed divided by transfer case output speed, both from real sensors. If the control module commands 4WD high and the result falls in the window for low range or for neutral, the fault counts. It needs 7 seconds of failure within a 10-second window, output shaft speed above 500 rpm, positive engine torque and pedal input, no PTO operation and no active speed sensor faults. GM rates it Type A, so the MIL lights after one trip. Likely reasons are a range shift that did not complete, a worn shift fork or a slipping range sleeve. P279B and P279C cover the other two states.
P279A at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyHard
- Typical labor1 to 8 hours
- Clears after repairAfter a drive cycle
Symptoms of P279A
- MIL and 4WD warning on
- Unexpected low-range feel or loss of drive
- Grinding from the transfer case
Common causes of P279A
- Most likelyRange shift to high not completed by the shift motor
- PossibleWorn shift fork or range sleeve slipping out of high
- PossibleImplausible transfer case output speed signal
- Less likelyMismatched tire sizes affecting the computed ratio
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Transfer casePlanetary gear setShift fork
What each part of P279A means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 2 | Generic code (second SAE range): it means the same on every make. |
| 7 | Area: transmission. |
| 9A | The exact fault in that area. |
What to do next
- Note P279A 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 P279A
What does P279A mean?
P279A means "Transfer Case Gear High Incorrect Ratio". P279A fires when the transfer case should be in its high range, but the measured ratio says otherwise. It is a generic code, so it means the same on every make.
Is it safe to drive with P279A?
Drive gently and only to a workshop. With P279A the car can go into limp mode (reduced power) to protect itself.
Will P279A fail an emissions test?
Yes, it can. P279A 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 P279A to fix?
Difficulty: hard. A typical repair takes 1 to 8 hours of work. This is a job for a workshop.
Will P279A clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.