I appreciate the advice and I will look into purchasing the oil and tester you mentioned. Do you know if other service centers can do repairs on Nissan with confidence or do I have to go to the Nissan serivce centers only? Also, can I manually turn off the service engine light by pulling a plug or a fuse? Someone at my office says if I disconnect the battery it will reset itself and the light will go off, is this true?

Thank you so much for all you advise and help. It's more than what I got from the guys I paid to do the repair work, even though the problem still exists.

On many cars, disconnecting the battery will reset the computer. Make sure to record any radio codes first. If there is a problem, however, the Check Engine Light will come back on.

I recommend taking Nissans to Nissan and Fords to Ford. Their service personnel are more thoroughly trained in servicing those vehicles. Many times, they are also cheaper, which runs counter to what many people think.

I placed some links on my original response that you should take a look at.

KEEP ME POSTED.