Nissan Repair: Service Engine Soon light is On for 1998 Nissan Altima, nissan altima, pep boys

Question
Hello
My Nissan Altima car has the Service Engine Soon Light on. When i went to diagonosis the car, the mechanics told me to replace the IAT sensor stating. They also told me to drive for about 200 miles. But after sometimes,like driving100 miles the light came on again. I went there again and now they are telling me to replace the Knock sensor. I also went to a Nissan delaer. But they gave me a different scenerio. They are telling me that knock sensor cannt turn the light off for Nissan 1998 altima and they are telling me to replace EGR BPT valve. I am really confused. Please help me what should I do.
thanks!

Answer
Mazmi,

This is easy if you have your own scanner.  The cost of a scanner at Checker and Pep Boys is about $60 bucks.  Buy one and then you can diagnose your own codes and tell the shop what they need to be correcting.  Also, the scanner can turn the light off.  So, if it were me I would buy a scanner and get the codes.  Them, turn the MIL off and see if it lasts.  If it does come back on you know that there is a problem and you can read the code.  Then get the part called for and replace it yourself and save even more money.  If you do not want to spend the money on the scanner you can take the car to Autozone and they will read the codes for free and then you will know what the codes really are.