Output Speed Sensor Circuit Direction Error
The P077B code indicates that the powertrain control module (PCM) has detected an inconsistency in the direction signal from the output speed sensor. This sensor monitors the rotational speed and direction of the transmission output shaft. The error suggests the sensor is reporting a direction (e.g., reverse) that does not match the expected direction based on gear selection or vehicle movement. This can be caused by a faulty sensor, wiring issues, or a misaligned sensor reluctor ring.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission may shift erratically or fail to shift
- Speedometer may be inoperative or inaccurate
- Vehicle may go into limp mode
2. Most Common Causes
- Faulty output speed sensor
- Damaged or shorted wiring/connectors to the sensor
- Misaligned or damaged reluctor ring on the output shaft
- Internal transmission mechanical failure
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and record freeze frame data.
Step 2: Inspect the output speed sensor and its wiring for damage, corrosion, or loose connections.
Step 3: Test the sensor's resistance and AC voltage output while rotating the wheels (or using a scan tool to monitor sensor data).
Step 4: Check the reluctor ring for damage or misalignment (may require transmission disassembly).
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The transmission may shift erratically or fail, potentially causing a safety hazard or further damage.
How much does it cost to fix?▼
Typically $50-$150 for a sensor replacement, but costs can increase if wiring repairs or transmission work is needed.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.