I recently replaced my thermostat due to an overheating problem. The overheat problem went away but I still have the yellow engine light. Do I need a code reader to make the code go away?

 

At a minimum you need to connect a scanner to the vehicle and see if a DTC is still locked in the DME memory. If it is, you'll need to clear it.

http://www.foxwellmall.com/

 

Be careful with that temp sensor plug, too. If you can get a realtime readout on that temperature, that's the best way to see what's wrong.

I had gone through 3 sensors on one MCS before, all the while, it's the sensor plug that has an issue, the prong got pushed off and couldn't be in contact with the sensor itself.

 

I have a $10 bluetooth code reader from amazon I use to clear codes with the torque lite app