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Q: Speedometer is erratic and the S light is on

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My speedometer jumps up and down and then stops working. Then the S light comes on. There is no loss in power and the transmission seems to shift properly. I have noticed it usually does this after the 2nd start of the car. If you turn the car off it goes out and the speedometer works fine again.

My car has 139000 miles.
My car has an automatic transmission.

A: There are a few different components that c...

There are a few different components that can cause these issues. The main one is the vehicle speed sensor (VSS). This is located on your transmission, and communicates to the engine what speed the transmission is receiving. The VSS also sends important information to your vehicle's computer, and this information eventually ends up on your dashboard.

The first thing you should do is have the vehicle scanned for codes. You will want to make the symptoms occur when running the test. This way, the scanner will be able to list what components are setting the warning light, and help you confirm or deny the VSS as the problem. I recommend having a professional mechanic, such as one from YourMechanic, complete an inspection to determine if there are electrical problems and why the speedometer is not working correctly.

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