P077A
Output Shaft Speed Sensor Circuit - Loss of Direction Signal
Transmission
Generic OBD-II
Medium
What it means
The output shaft speed sensor reports both how fast and which way the transmission output shaft turns. P077A sets when the direction portion of that signal is lost, so the control module can't confirm rotational direction. That can upset shift scheduling and direction-dependent features, usually because of a failing sensor, wiring fault, or a damaged reluctor ring.
Medium
Can I keep driving? Generally drivable, but shifting may be erratic and features like 4WD may not engage; have it checked soon.
Common symptoms
What you'll notice
- Erratic or harsh shifting
- Speedometer glitches possible
- Four-wheel drive may not engage (on equipped vehicles)
- May enter limp mode
- Check-engine or transmission warning light on
Common causes
Most likely first
- Faulty output shaft speed sensorLikely
- Wiring or connector fault, or corrosion, in the sensor circuitCommon
- Damaged sensor tone/reluctor ringCommon
- Contaminated fluid around the sensorLess often
- Transmission control module fault (less common)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and note any companion speed-sensor codes.
- Inspect the output speed sensor connector and wiring for damage or corrosion.
- Remove the sensor and inspect it and the reluctor ring for worn or missing teeth.
- Check transmission fluid condition — burnt or dirty fluid should be serviced.
- Test the sensor's signal and replace it if out of specification.
FAQ
Quick answers
Is it safe to drive with P077A?+
Usually yes for short trips, but shifting may be erratic and direction-dependent features like 4WD may not work. Get it diagnosed soon.
Can I just clear P077A?+
It returns whenever the direction signal drops out again. Repair the sensor, wiring, or reluctor ring to clear it for good.
Related codes
Often seen with P077A
Read & clear P077A yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX