Output Speed Sensor Range/Performance
The P0721 code indicates that the powertrain control module (PCM) has detected an output speed sensor signal that is out of the expected range or not performing correctly. This sensor monitors the rotational speed of the transmission output shaft, which is used for shift timing, torque converter lockup, and speedometer operation. A faulty signal can cause erratic shifting, incorrect speed readings, and transmission performance issues.
1. Symptoms You Will Notice
- Check Engine Light illuminated
- Erratic or harsh shifting
- Speedometer inaccurate or not working
- Transmission may go into limp mode
2. Most Common Causes
- Faulty output speed sensor
- Damaged or loose wiring/connectors to the sensor
- Contaminated or damaged sensor reluctor ring
- Internal transmission mechanical failure
3. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data
Step 2: Inspect output speed sensor wiring and connector for damage or corrosion
Step 3: Test sensor resistance and AC voltage output while rotating the wheels
Step 4: Check reluctor ring for damage or debris
Step 5: If sensor and wiring are good, suspect internal transmission issue
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive long distances as it can cause transmission damage or unsafe driving conditions due to erratic shifting or speedometer failure.
How much does it cost to fix?▼
Replacing the output speed sensor typically costs $50-$150 for parts and labor, but if internal transmission damage is found, costs can be significantly higher.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.