My check engine light came on in my wifes van so I had a mechanic at my work take a look at it. He hooked a computer up to the van that diagnosed the problem. (P0456). He replaced 2 hoses and then turned the car on and reset the computer in the van and the check engine light went off.

My question is, would the check engine light have gone off when he reset it with the computer if the problem wasn't fixed? I just want to make sure that the problem is really fixed and not just masked. Thanks.

 

Yes. But it would have come back on. The computer has set routines for testing each system. The car has to be started X number of times, run to operating temp X number of times, driven at x speeds for X minutes, etc, etc. These are called drive cycles. The computer watches the sensors during the drive cycles and if a reading is out of spec X number of times, then it lights the check engine light. Reset the code and you reset the drive cycle. Drive cycles are also called "monitors". When scanned, the computer can tell the mechanic whether it has completed all the drive cycles necessary to give an accurate picture of the vehicle's condition. That's why you can't just reset the computer and take it in for emissions testing. The inspector can see right away that the monitors have not "completed."