OBD-II code · Powertrain (generic)
P077A Output Shaft Speed Sensor Circuit - Loss of Direction Signal
The output shaft speed sensor uses a quadrature output (two channels phase-shifted by 90°) so the TCM can determine direction of rotation. The direction channel is missing — TCM cannot tell whether the vehicle is rolling forward or backward, blocking neutral-idle and rollback-protection strategies.
Is it safe to drive with P077A?
Usually safe to drive in the short term. Get it diagnosed when convenient, sooner if the car drives differently.
Common causes
- Most likelyOpen direction-channel wire
- PossibleFailed quadrature sensor element
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Repair at a glance
- Difficulty
- Medium
- DIY friendly
- Best left to a mechanic
- Typical labour
- 0.6–2.5 h
- Emissions test
- Usually unaffected
- Parts involved
- Output Shaft Speed Sensor, Sensor Wiring
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.