Powertrain, generic · Transmission

P077D Output Shaft Speed Sensor Circuit High

Check engine lightOn
EmissionsRelevant
Drive cycleNot required
Limp modePossible

GM's transmission modules from 2019 to 2025 (9- and 10-speeds) also read the active output speed sensor's line voltage as an analog value. P077D is the mirror of P077C: the voltage is above 4.75 V – a short to the module supply of under about 0.5 Ω – for more than 0.05 s, after one trip. GM then blocks the no-signal and ratio checks; a GM hybrid also blocks its idle diagnosis. Without usable output speed the transmission enters limp mode, and speedometer or cruise control may fail.

Likely causes

Signal wire shorted to sensor supply or battery voltage
Sensor faulty internally
Ground fault at the sensor, corroded connector
Module input

Symptoms

  • Check engine light at once (GM)
  • Limp mode
  • Speedometer or cruise control failed
  • Shift problems

Repair estimate

DifficultyMediumWorkshop job
Parts and labour€120–450
Time1–3 h

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

Parts involved

output speed sensorsensor wiringtransmission control module

Related codes

P077CP0722P0723P0721P0720

References: gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.