Piston Slap: Reprogramming smart car’s idiot light?

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YouTube/PDP Performance

Ed writes:

The “tire pressure” light lit up on our Smart for Two car. I serviced it to specs, but the light is still lit. How can I fix this?

Sajeev answers:

Sadly, I don’t know what “serviced it to specs” means, so let’s just start from the beginning. A TPMS (tire pressure monitoring system) diagnostic starts with the obvious first step: inflating the tires to their correct pressure. If that fails to extinguish the light, reset the light using this video.

Or not using this video, because I don’t know the year of this vehicle. (There are plenty of videos on YouTube for this particular issue, one will correctly reflect your vehicle’s year.) Speaking of age, if the sensors are 10+ years old, replace all of them. The sad reality is that the batteries are likely dead, and they are not serviceable. Once installed, get them reprogrammed at any tire shop. You don’t necessarily need Mercedes-branded sensors; four aftermarket units will likely work perfectly … for another 10 years or so.

MORESENSOR tire pressure sensors
MORESENSOR | Amazon

Make sure to shop around and find the best price on parts/labor on this work from nearby tire shops. They will use a tool like the one below to program the new sensors to work with the vehicle.

If this particular smart car is well under 10 years old (i.e. buying new sensors doesn’t make sense), the TPMS system needs to be tested for a bad wheel sensor, faulty control module, or even bad wiring. Many shops (especially those that specialize in German vehicles) have the software and the knowledge to make short work of this relatively simple system. Sadly, that’s all you can do, as there’s precious little a shadetree mechanic can do when it comes to TPMS sensors.

My best guess? Those sensors are around 10 years old and they all need to be replaced and reprogrammed. Best of luck!

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