Output Speed Sensor Circuit Direction Error
The P077B code indicates that the transmission control module (TCM) has detected an inconsistency between the output speed sensor signal and the expected direction of rotation. This typically occurs when the sensor reports a signal that does not match the actual direction of the output shaft, often due to a faulty sensor, wiring issues, or internal transmission problems. The TCM uses this signal to control shift timing and torque converter lockup, so a direction error can lead to improper transmission operation.
01. Most Common Causes
- Faulty output speed sensor
- Damaged or shorted wiring/connectors to the sensor
- Incorrect sensor installation or misalignment
- Internal transmission mechanical failure (e.g., broken tone wheel)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting harshly or erratically
- Vehicle may go into limp mode or fail to shift properly
- Speedometer may be inaccurate or not work
03. Step-by-Step Diagnosis
Step 1: Scan the vehicle for 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 signal output using a multimeter or oscilloscope.
Step 4: Compare sensor readings with known good values; if out of spec, replace the sensor.
Step 5: If sensor is okay, check the tone wheel for damage or debris and inspect transmission for internal issues.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances with this code, as it can cause harsh shifting, transmission slippage, or sudden failure. Limp mode may limit speed, but continued driving can damage the transmission.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for a sensor replacement if that is the issue. If internal transmission damage is found, costs can be much higher, potentially $1,000 or more.