Powertrain, generic (extended)

P27B4 Internal Control Module Transmission Gear Direction Control Performance

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

P27B4 concerns the direction in which the vehicle actually moves compared with the selected gear. GM's 2024 heavy-duty TCM tables compare the direction reported by the output speed sensor with the direction implied by solenoid and pressure switch states; disagreement for one second sets the code with MIL on the first trip. Ford's 2024 summary splits it into unintended launch (UDS P073D_48) and wrong driving direction (P073F_48), listed as non-MIL on eight- and ten-speed automatics. Despite that listing, Ford bulletins report a MIL and point to software: TSB 20-2074 for 2020 Super Duty trucks with 6.2 or 7.3 L petrol engines and the 10R140, TSB 20-2336 for the 6.7 L diesel, and TSB 26-2096 for the 2022 F-150 Lightning, where the wrench light comes from the SOBDMC.

Likely causes

Module software strategy (Ford reprograms PCM or SOBDMC)
Faulty direction information from the output speed sensor
Solenoid or pressure switch reporting a state that does not match the gear

Symptoms

  • MIL or wrench light
  • Forced idle or reduced power
  • Gear engagement blocked until restart

Repair estimate

DifficultyShop_onlyWorkshop job
Parts and labour€0–1,500
Time0.3–4 h

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

Parts involved

tcm

Related codes

P27B2P27B5P27B6P073DP073FP0720

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