Dreaded Volvo Check Engine light

The Car: 2000 V-70 Wagon Manual My third "Slovo:

The Issue: Check engine comes on-Usually when I use cheap 87octane gas (after my wife fills it) First came on after a heavy rain

The Suggestion: Other than keeping it happy with 92 octane, could this be an O-2 sensor? (as in cheap fix?)

No, it’s not lilely to be the oxygen sensor.

Yes, it might be a cheap fix. Even cheaper than the oxygen sensor.

There are two clues here: the 87 octane, which could be causing a tendency toward pinging (being compensated for by the knock sensor and tripping the CEL), and the rain. The rain clue could point to the need for a good thorough tuneup, which of you need one badly enough could be causing misfiring in the rain (tripping the CEL).

Perhaps it’s time for that overdue maintenance to be done. Perhaps having the stored codes read would be a good place to begin…before doing the tuneup.

That CEL (check engine light) is just a kid in class waving her hand trying to get you attention because she has the answer. You need to have the codes read. Some places will read them for FREE. Try Autozone or Advanced Auto Parts. Get the exact code (like P1234) not just their translation into English and post it back here. 

Why try blindly choosing something that might fix it, when all you need do is to ask her?

Well, I broke down and bought a $60.00 code reader and got the following codes:
P452=Evap emission control pres sensor low (can I get a definition for this?)
P455=Emission control system leak (large)(definition?)
These sounded suspisiously like a gas cap failure (these code as gas cap for different mfgrs) so I reset them afterwards and I got
P1670=Manufactuer control auxilary inputs auxilary outputs (?!?!?!?)
Does this sound like a faulty gas cap? The P455 code comes back within 10 minutes after erasing the code. I expect delivery of a fuel cap today.

By the way, here in foggy Northern California Autozone will not read the codes for you. They will print out the code discriptions for you, but Volvo is not in their database. They probably got sued for trying to do an end run around the Smog laws.

Your EVAP system is monitored by a pressure sensor that trips a CEL if the vacuum exceeds (or is less than) the normal range. It sounds like because of the EVAP system leak the light keeps tripping. The check here is called a “smoke test”. Smoke is piped into the void areas in the system and where the smoke leaks out is where the leak is.

This has no relationship to octane or to heavy rain. I still suspect you need a tuneup…and now suggest a smoke test.

This begs the comment: where there’s smoke there’s fire…never a good thing where the fuel tank is concerned.
The tuneup will be forthcoming. Can you recommend a national chain that conducts these tests?(or S/F. East Bay Area if you’re familiar). Is smoke sold in a can???

One furthur clue…I am having a very hard time filling the tank. The gas pump nozzle keeps tripping. THis indicates to me a fuel tank vent clog or failure. can anyone provide me a link or copy to/of a fuel/EVAP emissions diagram?

Good news. It looks like your codes are in agreement with your symptoms. Get that problem fixed first.

***P1670=Manufactuer control auxilary inputs auxilary outputs (?!?!?!?) ***

P1670 is a manufacturer specific code. It’s not all that easy to figure out what it is for a Volvo. Further, Ford uses that code for some sort of “feedback” problem. Here’s a link that says it might be "… the antennae of the immobilizer. It was replaced at a cost of Can$200. The car is working fine since. " (Note: I have never encountered a component called an “immobilizer”, and I don’t think I’d want to own a car that had one). http://www.brickboard.com/AWD/volvo/1100990/S70/obdii_code_nop1670_p1670_ob.html

Anyway, the rest of the stuff does sound like an evaporative emissions control system problem, but I’d guess maybe something meaningful busted rather than a bad/loose gas cap. On most cars gas cap issues seem to cause code P0442 and sometimes other codes in the P0440-450 area as well. Anyway, here’s a good site for OBD codes http://www.obd-codes.com/trouble_codes/ But it doesn’t address Volvo specific codes.

This often happens if you are in the habit of topping off the tank when you fill up.  Likely, if you look, you will find notices in your owner's manual and pasted somewhere on your car telling you NOT to top off the tank.  It can damage the vapor recovery system.

First if it has been a long time or your can't remember when the plugs were last changed, change them (same for the plug wires).  Get a new fuel cap, or make sure the one you have is closed tightly. Maybe you wife is not getting it closed tight.

What does your owner’s manual say about octane? If it says it needs high test, you can damage the car by using less, if it recommends high test, you may be wasting your money thinking low test can save you money as you generally get less mileage if you use low test on a car that “recommends” high test.

The good news is that with the possible exception of a damaged vapor recovery part or two (caused by topping off the tank) you should have little or no cost of repairs not not all that much cost of maintenance due.  

Remember maintenance is cheaper than repairs.  Things like new plugs wires, air, oil and fuel filters new oil etc. are good investments and pay back much better than the bank.