P279BTransfer Case Gear Low Incorrect Ratio
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- Needs a drive cycle to confirm a fix
- How the car detects it
- P279B is the reverse case of P279A: 4WD low has been commanded, yet the transfer case behaves like high range or neutral. For a vehicle crawling off-road this is a real safety concern, because the expected reduction and engine braking are missing. In GM's 2019 ECM tables (LCV section) the module divides transmission output speed by transfer case output speed and flags the fault if the result lands in the high or neutral window. Timing and conditions match the high-range test: 7 s of failure within 10 s, output shaft above 500 rpm, engine torque and pedal applied, no PTO and no active speed sensor faults; Type A, so one failing trip turns on the MIL. A shift motor that stalls before the low position, worn planetary teeth or a broken fork are the likely culprits. P279C covers neutral.
- What you may notice
- No reduction in 4WD low, weak crawling and engine braking
- 4WD warning lamp and MIL
- Clunking or grinding when selecting low range
- Likely causes
- LikelyShift motor stopping short of the low position
- PossibleWorn or damaged reduction planetary set
- PossibleBroken or bent range shift fork
- RareFaulty speed signal distorting the ratio
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €150 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.