P0721: Output Shaft Speed Sensor Circuit Range/Performance
What to do
Shifts may be erratic, and the speedometer may read normally at some speeds and wrongly at others. If the vehicle has recently had gearbox or driveshaft work done, mention it — a sensor not seated to depth gives exactly this.
What this code means
The output shaft speed signal is present but implausible — noisy, jumping, or disagreeing with the wheel speeds the anti-lock braking system reports. That last comparison is the useful one, because the vehicle already has four independent speed measurements at the wheels and the module can check its transmission sensor against them.
Mechanical causes deserve a look before electrical ones here. These sensors read a toothed ring, and the air gap between tip and teeth is small: a sensor not seated fully, a shim omitted after a repair, or a ring with a chipped tooth all produce a signal that is present but wrong. So does swarf bridging the gap.
Likely causes
Start here
- Faulty output speed sensor · moderate
- Damaged reluctor or tone ring · specialist
Less common
- Incorrect sensor air gap · moderate
- Metal debris on the sensor tip · specialist
- Damaged transmission wiring harness · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
Sign in or create an account to add what you found about P0721.