&gt; There is a downside to diagnostics tools being freely available, you can clear any fault codes before you sell the car to an unsuspecting buyer, this will prevent the dash warning lights appearing until the sensor registers the fault again, which could be under particular driving conditions.<p>This is already reality. Any AutoZone store, and probably most other large auto parts retailers, will read and clear codes for you at no charge. Their upside is that you might buy a part to fix the code.