Powertrain
generic / SAE
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.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number7 / 7A
Possible causes
- Open direction-channel wire high
- Failed quadrature sensor element medium
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
Inspection / repair
- Difficulty: medium
- DIY: shop recommended
- Estimated cost: 200–800 €
- Estimated time: 0.6–2.5 h
- Component: output shaft speed sensor
- Component: sensor wiring
- MIL / check engine light
Sources
References
sae:J2012