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Check Engine Light-Fault Code:P0420-2(four possible causes?)

Help and Advice on S40, V40 and V50. In this forum you'll find S40/V40/V50-specific owners asking and answering questions on maintenance, ownership, repairs, tutorials and almost every do-it-yourself thing you can do to save money owning these Volvos.
1996 - 2004 S40
1996 - 2004 V40
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Check Engine Light-Fault Code:P0420-2(four possible causes?)

Postby Blue Colnago » 10 Dec 2006, 05:48

1. The issue is with my wife's 2004 S40T. It has 78ki miles on it. A few weeks ago the check engine slight started coming on for a few days, then would go off for a few days. The dealer charged us $100 us to diagnose the problem, which turned up the error code "ECM-A1" which apparently means " Electronic Coolant Temperature Sensor and Thermostat" . The total bill, parts, labor and diagnosis was $314 dollars. So we pony up the dough and get it fixed.

2. A few days ago the check engine light came on again, and then goes off again, same as last time. I get on the internet, do some searching and figure out that Autozone can read the fault codes for free. So I find one and go. This time, the code reads something different: P0420-2. I ask him to translate that and he looks in the book and comes back with four possibilites. He says the first is most likely, and the last is least likely.

1. Catalytic Converter
2. Engine Misfire, or running problem.
3. Large Vacuum Leak
4. Engine Oil leakage into Exhaust Valve Guide Seals.

Primary Question: Did I get four dif answers because I went to autozone and got a freebie? If I had gone right back to the dealer would they give me a more conscise answer, or do they have to play detective too? The engine leak sounds the most serious to me, and since it about the only thing I know how to do, I've checked the oli level and its ok. The engine seems to be running smooth and is not mis-firing. Q: Are any of these 4 things serious enough to require immeadiate service?

I don't need direction on how to fix this myself. But, at age 45 I'm getting fed up with not understanding cars. If I can just get to the point where I can speak with my dealers service people in a knowledgeable way, my wife and I could stop feeling like easy marks when we walk in the door. I've been investigating this here, and in other forums and have gotten a little confused over some of the lingo and terminology.

Things standing in my way of understanding the larger issue:
1. What is a CEL ?
2. What does OBD stand for
3. Is this particular problem in anyway related to a recall?
4. How would I know if the check engine light is sending me a curve ball?
if there's nothing actually wrong, what would it read? How do you EVER know if the warning light system itself is malfunctioning.
5. Is checking the gas cap always on the list of things to try first?
6. Is switching to higher octane fuel always on the list of things to try first?

Thanks in advance
ï 2001 S60 2.4L Non Turbo, 85k: Me

ï 2001 S40 1.9t, 85k: Wife

ï Bolingbrook, Illinois
Blue Colnago
Posts: 4
Joined: 10 Dec 2006, 00:15

Postby MadeInJapan » 10 Dec 2006, 06:04

When I see that code and look it up, I get "Catalytic Effeciency Below Threshold (Bank 1)" Bank 1 usually refers to the front 02 sensor (you have 2, one before the CAT and one after it). Somehow the front 02 sensor isn't sending enough of a signal to render the CAT to be effecient as it should be...the second 02 sensor will sense the difference between itself and the front one and register the data as to how the CAT is doing. Your condition unfortunately could be caused by several different things and that's why AutoZone tells you 4 different possibilities. Pursue each one by how simple it is and by cost. Sure, the CAT could be going bad but then you usually will smell it (rotten eggs) and you will have some thick exhaust. I don't know where he's getting engine seal issues. With a misfire, you would usually get other codes. I suspect a large vacuum leak somewhere. Have you tightened your gas fill cap really good? Did you fill up recently? If it is loose it could cause a large vacuum leak. Could be as simple as that or one of your vacuum hoses or vacuum hose elbows springing a leak. Check these out first.

CEL= Check Engine Light
OBD= On Board Diagnostic System (you have a place near your dash and steering wheel...I'm not sure exactly on your car, where you hook up a scan tool to read the codes). The system to check your codes is the OBD. On your car you should have an OBD-II (second edition of sorts) system.
The warning system light on Volvo's hardly ever malfunction. In fact they are usually more sensitive than they ought to be. So if a CEL comes on, there is a good reason. Take it as a warning and don't drive your car unless you figure out the codes. In your case, none of the codes are going to ruin your car (such as engine, coolant, transmission codes). In your case, I would be most concerned (as you, wisely are too) of an engine seal oil leak, but if you have no indication of this, I would rule this out as the culprit pretty quick.

You never said how your car was driving. Is there rough idling, cutting out, misfires, etc.? Do you have any oil leaks...losing coolant, etc.? If there are not concerns except for the light being on, then tighten your gas cap really good (several clicks) and drive your car for awhile. If that was the issue, the light will go away on its own.

Oh, by the way, with a turbo you should always use better than the lowest priced gas. Check your owners' manual and stay with what it says. However, I don't suspect that as being the culprit.

Good luck!
'98 S70 T5 Emrld Grn Met/Beige Tons of Upgrades Mobil-1
'04 V70 2.5T Red/Taupe Some Upgrades Mobil-1
94 850 Sedan NA Drk Blue/Tan
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Postby Blue Colnago » 11 Dec 2006, 05:29

Wow, Thanks made in Japan -

You've covered my questions so thoroughly I have nothing more to ask or add. can only say Thank you for taking the time with explain this to me. I'll be snooping around here trying to figure out the common volvo headaches. Might See you 'round the ranch sometime.

- Jack
ï 2001 S60 2.4L Non Turbo, 85k: Me

ï 2001 S40 1.9t, 85k: Wife

ï Bolingbrook, Illinois
Blue Colnago
Posts: 4
Joined: 10 Dec 2006, 00:15

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