Code
P077F
Generic
P — Powertrain
Reverse 2 Incorrect Ratio
Views:
UK: 25
EN: 35
RU: 26
AI status
Completed
Completed
100%
Causes
- Low, dirty, or overheated transmission fluid
- Worn or burned reverse clutch pack or band
- Failed or sticking shift/pressure control solenoid(s)
- Valve body faults or debris-clogged passages
- Faulty input or output speed sensor (incorrect speed reading)
- Damaged planetary gearset or internal transmission component
Symptoms
- Check Engine/Transmission MIL illuminated
- Harsh, delayed, slipping, or no engagement in reverse (Reverse 2)
- Transmission may enter limp/low-gear mode
- Abnormal transmission noises when selecting reverse
- Inconsistent vehicle reverse speed or inability to hold reverse
- Possible fluid leakage or burnt-smelling fluid
What to check
- Read freeze-frame data and full scan tool DTC list (check for related codes)
- Verify transmission fluid level, color, and smell (burnt)
- Monitor live data: input & output speed sensors, commanded gear, torque converter status
- Check shift/pressure solenoid activation status with a scan tool
- Inspect wiring and connectors to TCM, solenoids, and speed sensors
- Check for TSBs or software updates for transmission/TCM
Signal parameters
- Transmission input speed (rpm) — engine or turbine speed from sensor
- Transmission output speed (rpm or vehicle speed) — wheel/shaft sensor
- Computed gear ratio = input_speed / output_speed (TCM compares to expected)
- Shift solenoid/pressure control solenoid command state (ON/OFF or PWM duty)
- Transmission line/servo oil pressure (psi or kPa) during reverse
- Torque converter engagement/lock-up status and torque converter pump speed
Diagnostic algorithm
- Retrieve and record all codes and freeze-frame data. Note vehicle conditions when fault set (temp, speed, throttle).
- Inspect transmission fluid level and condition; correct level and replace fluid/filter if contaminated or burnt.
- With scan tool, monitor input and output speed sensors while selecting reverse 2. Confirm whether actual ratio differs from expected; repeat test to confirm fault is repeatable.
- Check electrical: inspect connectors, pin corrosion, and wiring continuity for speed sensors and solenoids. Wiggle-test harness while monitoring for signal changes.
- Command the shift/pressure solenoid(s) for reverse 2 using a bi-directional scan tool and observe response and current draw. Replace solenoid if stuck or out of spec.
- Perform transmission line pressure test during reverse engagement; compare to factory specification. Low pressure suggests hydraulic leak, faulty pump, or internal wear.
- If electrical and hydraulic tests pass, remove valve body (if applicable) to inspect for debris, scored valves, or sticking valve spool affecting reverse circuits.
- Inspect clutch pack and band components (if accessible) for wear or burn. If internal friction components are worn, a rebuild or replacement may be required.
- Check for and apply any required TCM software updates; clear codes and retest after repairs.
- If repairs performed, validate by road test and re-scan to ensure P077F does not return.
Likely causes
- Low or degraded transmission fluid affecting hydraulic clamping force
- Sticking or failed shift/pressure solenoid for the reverse 2 circuit
- Worn/clutch pack or band specific to the reverse 2 ratio
- Faulty input/output speed sensor or poor sensor signal
- Valve body malfunction or contaminated valve body passages
Fault status
Status
TCM detected incorrect gear ratio for Reverse 2 — actual input/output speed ratio outside expected range.
Repair difficulty: Hard
Diagnostic time: 2-8 hours
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