P215B: Vehicle Speed - Output Shaft Speed Correlation
What to do
Say whether the wheels or tyres have been changed, including to a different size or profile. This is the commonest cause by a wide margin — a different rolling circumference means wheel speed no longer converts to road speed correctly, and it also puts the speedometer out.
Mention a space-saver or mismatched spare if one is fitted, since that produces this immediately.
Mention any gearbox or differential work. A differential of a different ratio, or a vehicle set up for the wrong variant after a repair, produces a consistent permanent error.
Say whether the speedometer reads differently from a satellite navigation speed, which is a useful and free check you can do yourself.
What this code means
The vehicle speed and the transmission output shaft speed do not agree.
These two figures come from different places and are linked by a fixed ratio, which is what makes the comparison possible. Output shaft speed is measured at the gearbox; vehicle speed is derived from the wheel speed sensors. Between them sits the final drive — a fixed gear ratio — and the rolling circumference of the tyres. Given one, the module can calculate the other, and it does.
So a disagreement means one of three things has changed.
- A sensor is wrong. Either the output speed sensor or the wheel speed inputs.
- The ratio is not what the module thinks. A differential swapped for one of a different ratio, or a vehicle configured for the wrong variant, produces a permanent, consistent error.
- The tyres are not the size the module assumes. This is by far the commonest cause — a change in wheel or tyre size alters rolling circumference, so wheel speed no longer converts to road speed correctly.
That last one is worth asking about directly, because owners rarely volunteer it. Fitting larger or smaller wheels, or a mismatched spare, changes this relationship immediately — and on many vehicles it also puts the speedometer and odometer out.
There is a second reason manufacturers watch this, worth knowing: a mismatch is one of the signatures of a device fitted to falsify road speed or mileage.
Likely causes
Start here
- Incorrect tyre size or final drive ratio · moderate
- Faulty output speed sensor · moderate
- Faulty wheel speed sensor · moderate
Less common
- Incorrect final drive or tyre calibration after repair · specialist
- Damaged reluctor or tone ring · moderate
Symptoms
Components involved
Information, not instruction
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Community experience
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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.
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