I have a 97 850 Wagon with about 310,000 mi on it. Its been problem free for a while so I guess its due for something to go wrong, lol. My check engine light came on a couple days ago. I just got a hold of an OBD2 scanner and I got the code P0442. When I look up the code it says "Leak Diagnostic, Major Leak". This seems very vague. Anybody have a better description for this code or know what might be leaking?

 

"Evaporative Emission Control System Leak Detected (small leak)"

https://volvoforums.com/forum/volvo-s70-33/p0442-5714/

The above code seems to belong to the S70 lineup, but it probably applies to 850s as well. Most likely you have a small leak somewhere in the EVAP system; see attachment for possible cause.

My factory manual didn't have info on P0442, so you may want to google or wait until other experts chime in.

JPN

 

Well I cleared. I will have to see if it comes back. But, it sounds like this isn't a major thing?

 

Did someone else fuel your car? This code can be caused by a gas cap not screwed all the way on after fueling. Or the gasket on the gas cap may no longer be sealing 100%.

Then there's .

 

Here's an update on the issue. I have about 200 miles on since I cleared the code and the check engine light hasn't come back on yet. I haven't checked for leaks anywhere using the diagram provided by JPN yet. Thought I would wait to see if the CEL comes back on again.

@migbro - nobody else has fueled my car and I always turn the cap 3 clicks

I did put gas in today and checked my mpg (miles on trip/gallons put in). It has dropped from a little over 26mpg to about 24mpg. I don't think the EVAP System would have anything to do with this but, thought I would mention it just in case.

 

Does anybody have any input on this statement? Could a leaking/malfunctioning EVAP system cause a drop in mpg?

 

No...

 

Ok, thanks.

My mpg usually drops in the winter. I just don't remember it being that noticeable.

 

If there is a leak in the EVAP system, gasoline escapes in the form of vapour; a drop in mpg. You may want to do an inspection as fuel vapour is not only wasteful but is a fire hazard.

JPN

 

It could, depending on where the leak is. I doubt it would be a 2mpg drop though

 

Well I replaced the hose that supplies vacuum to the EVAP system. The orignal hose was a little short and had come out of its retainer clip. It was rubbing on the clip and was wore very thin. I couldn't see a hole but, replaced anyway. I also put some dielectric grease on the fuel cap gasket. I have had a couple tanks of gas through it with no more CEL. I think if it comes back on in a while I will assume the dielectric grease wore off and will need to replace fuel cap gasket if available or the whole fuel cap. Thank you

 

When standing still, YES.
When running it's a vacuum leak as the system is held under a minute vacuum and the loss of that static vacuum is what sets off the code.
Being a vacuum leak it would lean the engine out and possibly not reduce but increase the mileage.
It's more an engineers discussion as the amount of leak is pretty small.

 

Well I've come to the conclusion that the mpg drop I noticed is most likely the usual winter mpg drop that I get. I just didn't remember it being that much of a drop and CEL and drop happened at about the same time.