What Does P0721 Mean?
The output speed sensor (OSS) circuit is reporting readings outside the expected range or not correlating properly with vehicle speed, engine RPM, and gear selection. The OSS measures transmission output shaft speed, which the TCM uses to calculate vehicle speed and determine shift points. The driver may notice erratic speedometer readings, incorrect shifting, or transmission slipping sensations.
Common Causes
30%
Faulty output speed sensor producing erratic or out-of-range signal
25%
Damaged or corroded wiring and connectors in the OSS circuit
20%
Damaged or contaminated reluctor ring/tone wheel on the output shaft
15%
Incorrect sensor air gap or loose sensor mounting
10%
Internal transmission issue affecting output shaft (worn bearings or gear play)
Diagnostic Steps
1
Monitor the OSS PID in live data while driving. Compare the output speed to the speedometer and input speed sensor. The readings should be proportionally consistent with the current gear ratio.
2
Check the OSS reading at various steady speeds. It should be smooth and stable — erratic fluctuations indicate a sensor, reluctor, or wiring issue.
3
Inspect the OSS connector for corrosion, moisture, or damage. Verify the connector is fully seated and locked.
4
Remove the sensor and inspect the tip for metallic debris. Also inspect the reluctor ring (if accessible through the sensor bore) for damaged or missing teeth.
5
Measure the sensor resistance (typically 300-1,200 ohms for magnetic pickup type). Compare to manufacturer specification.
Estimated Repair Cost
$100 - $500
Parts + labor, varies by vehicle and location
The output speed sensor (OSS) circuit is reporting readings outside the expected range or not correlating properly with vehicle speed, engine RPM, and gear selection. The OSS measures transmission output shaft speed, which the TCM uses to calculate vehicle speed and determine shift points. The drive...
The most common cause of P0721 (Output Speed Sensor Circuit Range/Performance) is: Faulty output speed sensor producing erratic or out-of-range signal
Typical repair costs for P0721 range from $100 to $500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An erratic output speed signal can cause the speedometer to read incorrectly, affecting cruise control and ABS function. The transmission may shift at wrong speeds or enter limp mode. Drive cautiously and have it repaired soon.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0721 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Generic (SAE)
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