P077FReverse 2 Incorrect Ratio
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Can trigger limp mode
- How the car detects it
- P077F checks the ratio in a second reverse gear: input speed divided by output speed lies outside the tolerance band around the target ratio – a slipping clutch, a wrong gear or a sensor fault. Only transmissions with two reverse ratios need it, such as Mercedes' 7G-Tronic (−3.42 and −2.23, with the second reverse kept in limp mode) and its 5G-Tronic predecessor; GM's 9- and 10-speeds, Ford's 10R and ZF's 8HP have one. No manufacturer document available to us uses this code; the check works like the other ratio codes such as P0736.
- What you may notice
- Reverse slips or engages late
- Limp mode
- Transmission warning or check engine light
- Likely causes
- LikelySlipping clutch or brake in the second reverse power path
- PossibleFluid level low or fluid worn
- PossibleSolenoid or pressure regulator sticking
- RareFaulty input or output speed sensor
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Hard · Usually a job for a workshop.Typical cost: €200 – €3,500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.