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.
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.
Common causes
- high
Open direction-channel wire
One of the most commonly reported causes for this code — check this first.
Typical part cost: $220-880
- medium
Failed quadrature sensor element
A plausible cause — test and verify before replacing parts.
Typical part cost: $220-880
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Related codes
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Frequently asked questions
What does P077A mean?
P077A means "Output Shaft Speed Sensor Circuit - Loss of Direction Signal". It is a generic OBD-II code that points to a fault in the transmission.
What are the most common causes of P077A?
open direction-channel wire; failed quadrature sensor element — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
This code points to a problem that can cause damage or affect safety. Avoid driving and have the vehicle diagnosed promptly. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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