Brought my car to the mechanic, 2001 volvo s40, and when I started it, the service light came on. I just kept on driving and after a little bit it would turn off. It turned on every time i started it up. Then after about a week, i started the car, and the check engine light came on.

any suggestions as to what went wrong?

 

Service Engine light means you need to have the oil and filter changed. It triggers at 7500 miles and is not related to the Check Engine Light. It simply is a reminder to service the engine. After you change the oil and filter then turn off the light: key off - press and hold trip mileage reset thingy, turn iginition key to ON (not start), wait for Service Engine light to start flashing then release trip mileage reset thingy then turn key to OFF.

Check Engine light means the engine computer thinks something is wrong. Take the car to an Autozone or Advance or O'Reillys (etc) and have the trouble codes read for free. The OBD-II plug is next to your right knee as seated in the drivers seat, just beyond the plastic surrounding the center console.

The code(s) could be many things so report back what you find. Common ones are O2 sensor bank 1 or Coolant Temp Sensor. There are many others.

 

thanks so much Hudini