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.
Medium severity. Can I keep driving?Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
Symptoms
- Reverse slips or engages late
- Limp mode
- Transmission warning or check engine light
Most likely causes
- Slipping clutch or brake in the second reverse power path
- Fluid level low or fluid worn
- Solenoid or pressure regulator sticking
- Faulty input or output speed sensor
What to check, in order
Start with the simplest. You can tick off each step.
Good to know
- Repair difficulty: hard
- It can trigger limp mode.
- It affects emissions.
What each character of P077F means
- P: Powertrain: engine and transmission
- 0: Generic code: same on every make
- 7: Transmission
- 7F: Specific fault in that system
Frequently asked questions
Can I keep driving with code P077F?
Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.
What causes code P077F?
The most common causes are: slipping clutch or brake in the second reverse power path; fluid level low or fluid worn; solenoid or pressure regulator sticking.
Related codes
- P0736Reverse Incorrect Ratio
- P0730Incorrect Gear Ratio
- P0715Input/Turbine Shaft Speed Sensor A Circuit
- P0720Output Shaft Speed Sensor Circuit
- P0729Gear 6 Incorrect Ratio
Sources
- en.wikipedia.org: Mercedes Benz 7G Tronic transmission
- law.cornell.edu: 13 CCR 1968.2
- newtonnet.co.uk: fordobd2012
Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.