Powertrain, generic (extended)

P2838 Shift Fork B Position Circuit Low

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

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.

Likely causes

Fork B sensor signal wire chafed through to ground
Sensor output no longer producing pulses
Break in the signal or supply wire leaving the input low

Symptoms

  • 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

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€150–2,500
Time1–6 h

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

Parts involved

shift fork bshift fork position sensor bwiring harness

Related codes

P2839P2836P283AP2837P2833P0642

References: gsi.ext.gm.com, fordservicecontent.com, static.nhtsa.gov.