I have a Jeep Cherokee 2000 with check engine light. The lights came up about a couple of months ago and I've been too lazy but now the inspection is due. Autozone rep read the codes and the printout suggest I replace Leak Dectection Pump. How reliable is their diagnosis? The 4 codes are

P0456 Evap Emission System Leak Detected (very small leak)
P0442 Evap Emission System Leak Detected (small leak)
P0455 Evap Emission System Leak Detected (gross leak/noflow)
P303 Cylinder 3 Misfire dectected

From what I have read and seen on Youtube, this could be a lot of things other than LDP. And P0303 could be totally something else. Should I trust their computer printout and start with LDP replacement? Any help would be greatly appreciated.

 

Could be one of those things where a problem just snowballs but there really are not additional problems. If time was not an issue and because it is not too expensive if this were me I would throw an new gas cap on, clear all the codes, drive around, and see what happens. Many times with a P0456 that is all it is. I would suggest you take it off and put it back on but you did say this started awhile ago and I am going to assume you have filled up numerous times since the Jeep threw the CEL.