Code result
P077A
Output Shaft Speed Sensor Circuit - Loss of Direction Signal
High severity
What it means
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?
No — stop driving
This code points to a problem that can cause damage or affect safety. Avoid driving and have the vehicle diagnosed promptly.
Most likely causes
Open direction-channel wire
highOne of the most commonly reported causes for this code — check this first.
Failed quadrature sensor element
mediumA plausible cause — test and verify before replacing parts.
Related help
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