P077COutput Shaft Speed Sensor 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
- 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. P077C means this voltage is below 0.25 V – a short to ground of under about 0.5 Ω between signal and module ground – for more than 0.05 s with the system above 10 V; GM rates it after one trip. GM then blocks the no-signal and ratio checks so that P0722 is not set instead of the actual short. Without output speed the transmission enters limp mode and road speed may be missing. On GM's 10-speed input and output sensors share a supply.
- What you may notice
- Check engine light at once (GM)
- Limp mode or fixed gear
- Speedometer or cruise control failed
- Harsh shifts, no converter lock-up
- Likely causes
- LikelySignal or supply wire shorted to ground (chafing at the case)
- PossibleSensor shorted internally
- PossibleOil or moisture in the connector, corrosion
- RareModule input faulty
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Usually a job for a workshop.Typical cost: €120 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.