P077D code meaning
Output Shaft Speed Sensor Circuit High
Powertrain system Generic code P07xx codes Check engine light
What P077D means
GM's transmission modules from 2019 to 2025 (9- and 10-speeds) also read the active output speed sensor's line voltage as an analog value. P077D is the mirror of P077C: the voltage is above 4.75 V – a short to the module supply of under about 0.5 Ω – for more than 0.05 s, after one trip. GM then blocks the no-signal and ratio checks; a GM hybrid also blocks its idle diagnosis. Without usable output speed the transmission enters limp mode, and speedometer or cruise control may fail.
P077D at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modePossible
- Repair difficultyMedium
- Typical labor1 to 3 hours
- Clears after repairWhen cleared with a scanner
Symptoms of P077D
- Check engine light at once (GM)
- Limp mode
- Speedometer or cruise control failed
- Shift problems
Common causes of P077D
- Most likelySignal wire shorted to sensor supply or battery voltage
- PossibleSensor faulty internally
- PossibleGround fault at the sensor, corroded connector
- Less likelyModule input
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Output speed sensorSensor wiringTransmission control module
What each part of P077D means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 0 | Generic code: it means the same on every make (SAE standard). |
| 7 | Area: transmission. |
| 7D | The exact fault in that area. |
What to do next
- Note P077D and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P077D
What does P077D mean?
P077D means "Output Shaft Speed Sensor Circuit High". GM's transmission modules from 2019 to 2025 (9- and 10-speeds) also read the active output speed sensor's line voltage as an analog value. It is a generic code, so it means the same on every make.
Is it safe to drive with P077D?
Drive gently and only to a workshop. With P077D the car can go into limp mode (reduced power) to protect itself.
Will P077D fail an emissions test?
Yes, it can. P077D is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P077D to fix?
Difficulty: medium. A typical repair takes 1 to 3 hours of work. This is a job for a workshop.
Will P077D clear itself after the repair?
Clear the code with a scanner after the repair. If the fault is fixed, it does not come back.