On trip yesterdy, odo went over 50 K miles on first leg. Next time I started up , check engine light came on, and stayed on until about third time started up, at over 50,250. In the meantime, the dealer service dept had given me a lot of gabble over the phone--"it'll probably be safe to drive, but don't blame us if it isn't, since you're out of warranty now.." No light this morning. Is this one of the "suck 'em into the dealer one more time" gimmicks built into the vehicle? While waiting for a callback from the dealer, I had checked all the fluids, air filters, visible wiring and hoses, and found nothing exceptionable. Vehicle ran normally the whole time.
Only mods that could be connected are K&N filter for past 15K miles and permacap gas tank cap, ditto. New Magnefines on trans and power steering after flush, about 5K miles back.
Any suggestions on what I should check myself, and what codes to check for, since the light is now out?

About 15 minutes after first post, went out & started car again--check engine light on. Borrowed a car-just got back from trip. Anybody have concrete suggestions re checking/clearing codes while I wait for the magic gadget to arrive? Or on probable safety of continuing to drive while waiting for code reader? Thanks

Ambient temps yesterday around 100F; idiot light on every time I started car. This morning, ambient temp only about 80F, drove the damn thing all over town till temp guage got to usual operating temp, and light never came on.
I'm over 100 miles from dealer, so will take to local indy with OBDII and let him play with it for a couple of days--I assume he'll need to get the light to come on before there are codes to tell anything. Meantime,while driving ancient carbureted truck, will appreciate suggestions re which brand of OBDII to shop for--preferably fairly near idiot-proof, since I'm not a mech/tech type.

My guess would be that the seal on the gas cap from IPD or where is bad. I don't think the perma-cap seals as good as the normal gas cap.
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1980 244DL, 1982 245GL, 1987 744GLE, 1991 245SE, 1996 855GLT, 2001 V70

That sounds as reasonable as anything else. Car was at the shop for two days, being run all over, and they couldn't get the check engine light to go on. However, outside temp has dropped from around 99F when it first occurred to around 75-80F. Would a minor defect in sealing show up with the temp differential in a way that would set off the light only when the temp went up? or is this a sign of impending failure of the oxy sensor somehow related to the air density as an inverse function of the temp? Maybe it's global warming combined with some sort of Wiccan conspiracy.Never a good exorcist around when you need one. Does Orkin do trolls?

As others have pointed out, an OBDII code reader will help you read and clear codes. There is but one caviat. No generic OBDII reader will read Volvo proprietary codes. And the most frequent causes of the CEL are Volvo codes 611 and 612 which are Volvo proprietary codes for gross and fine fuel vapor leak (don't remember which is which). In other words your gas cap is not on tightly or you may have fueled up with engine running. The generic code reader I have was not able to read those codes, but was able to clear them (!) and extinguish the CEL.

You mention that you have some aftermarket gas cap. My suggestion: loose it and go back to OEM. Those gas tank vapor recovery systems are very finniky about every little component, gascap being one of the more relevant ones.

Good luck.
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Vladimir. 1998 S70. Base, 5-speed manual.

My advice to you and others in your position is to buy a scan tool for about $150 at Autozone or other supplier, so that you can read the codes yourself. I have an Actron CP9035 and it does the job and comes with a book of the generic codes, which covers a lot of Volvo's codes. This shure took the mystery out of spurious check engine lights.

Larry is right on the money with that suggestion. Everything else that you might do to try to diagnose this (apparently intermittent) problem will be merely speculation until you retrieve the code that tripped the light in the first place.

BTW, the best deal I've seen so far on an OBDII reader is at http://www.jeepersandcreepers.com/gear/pages/equus.htm. I bought this one for use on my '99 S70 T5, and it helped me diagnose a faulty mass air sensor that the dealer couldn't figure out in three previous service attempts. That was 700 miles before the 50K mile warranty ran out.

You'd be smart to get a subscription (or CD) for Alldata, as well. That will tell you the meaning and service procedures for Volvo's proprietary codes that aren't included in the standard set of OBDII codes. http://www.alldatadiy.com/

Hope that helps.

Jim Rothe
'99 S70 T5M
http://www.monmouth.com/~rothe/carstuff.html#Volvo
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'99 S70 T5M

a loose gas cap will make the check engine light go on.