P2838Shift Fork B Position Circuit Low
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P2838 is stored when the fork B position input reads at the bottom of its range. The Corvette's rod 2 sensor, fed by GM from the same 5 V reference A as rod 1, has to send a pulse-width signal; if pulses are missing while the pin is below 2.0 V, or the duty cycle drops under 8 %, the module waits 150 ms and logs a Type A fault. Faults of reference A itself (P0642, P0643) suspend this test, so a supply problem shows up under those codes and tends to hit rod 1 as well. Ford's TR9070 summary describes the pattern for rod sensor 2 as a pulse width below its window with the input stuck at zero. Mercedes-Benz reads P283800 on the 8G-DCT as a fork B sensor shorted to ground. Gears on that rod are then locked out.
- What you may notice
- Warning lamp with transmission in limp-home mode
- Gears on rod 2 or fork B no longer selected
- Rough or delayed shifts around the locked-out gears
- Likely causes
- LikelyFork B sensor signal wire chafed through to ground
- PossibleSensor output no longer producing pulses
- RareBreak in the signal or supply wire leaving the input low
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €150 – €2,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.