Powertrain, generic (extended)

P2839 Shift Fork B Position Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

P2839 covers the other end of the scale: the fork B input is pinned high. GM's 2023 Corvette table for rod 2 sets it when pulses stop and the pin carries more than 3.5 V, or once the duty cycle passes 92 %. The test runs all the time except during cranking, and only while system voltage lies between 8.75 and 18 V and reference A between 4.5 and 5.5 V; 150 ms of the condition produce a Type A code. Ford's TR9070 lists P2839 for rod sensor 2 when the pulse width climbs above its window and the input stays at one, and on the 8G-DCT Mercedes-Benz reserves it for a fork B sensor with a short to battery positive. Check the harness for a signal wire rubbing against a supply line and confirm the sensor ground before replacing the sensor or module.

Likely causes

Signal wire of the fork B sensor touching the 5 V or battery supply
Open sensor ground letting the output float high
Sensor output stage stuck in the high state

Symptoms

  • Warning lamp and fault message in the cluster
  • Fork B gears blocked, fewer gears available
  • Reduced acceleration in the substitute program

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

P2838P2836P283AP2837P2834P0643

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