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Registered
2002 Deville
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33 Posts
Discussion Starter #1
Hello im having a code come up on my 2002 cadillac. The code is p0300 and I know its multiple or random misfire. I changed the spark plugs and it didnt work. I know it could be the ignition coils but how do I test for that? I dont want to have to buy expensive parts if its not the problem. The car studders when idling and driving. Any help is much appreciated thank you
 

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Super Moderator
2003 Deville Base
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4,819 Posts
Re: p0300

if I remember correctly, the P0300 only tells you that there IS a misfire but it won't tell you what cylinder. Find a parts store or mechanic with a Tech II scanner and they can tell you which cylinder to look at. Don't throw parts at it until you know for sure what part.
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,481 Posts
Re: p0300

Boots clean and not carbon tracked ? Connector springs tight ? Coil cassette ground springs clean and "springy" ? ICMs clean and properly connected ? Fuel injector connectors properly connected ?? FPR vacuum line in place, no breaks or vacuum leaks ? NO fuel in the FPR nipple with engine running ?
 

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Registered
2002 Deville
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33 Posts
Discussion Starter #4
I didn't look at the springs and boot. But I definitely will this weekend. And I will find a tech II scanner. Thank you for helping me out
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
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19,275 Posts
Re: p0300

I didn't look at the springs and boot. But I definitely will this weekend. And I will find a tech II scanner. Thank you for helping me out
=======================
And I will find a tech II scanner.
most large auto parts stores will check codes for free -
 

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Super Moderator
2003 Deville Base
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4,819 Posts
Re: p0300

^^^^^what he said. If you want to buy a genuine Tech II be prepared to open your wallet really wide.
 

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Registered
1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Re: p0300

If you've only got a p0300 code, then going to the parts store to get your codes checked won't help, because you've already checked your codes, and it's just p0300. Anybody else following the logic here?

I'd say Sub's on the money. P0300 is a vague code, and everything he mentioned should be checked. On Chrysler and Ford products, it is commonly a crankshaft or camshaft position sensor that has gone out, though if given a little time, they will usually set a code. Check sensor wiring to all the heavy hitters under the hood if Sub's advice doesn't get you an answer. Sometimes one will burn up, rub through, the clip will deteriorate, or if you did any other work recently, you may have disconnected one and reconnected, but just not quite tight enough.
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
Re: p0300

Before you do anything, I'd give the TB a good cleaning. Hard as it may be to believe, a dirty TB has been known to cause a misfire and throw a P0300 code.
 

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Super Moderator
2003 Deville Base
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4,819 Posts
Re: p0300

rat, I follow your logic; plus sub is detailed as always. Still, on a vague code, I think I'd want to know exactly where the problem originated.
 

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Registered
2001 Seville STS, 1990 Seville (RIP), 1972 Sedan Deville
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26,323 Posts
Not that I think it's necesarilly the issue, but a TB cleaning is yearly maintenance anyway. Might as well do it and have the add benefit of eliminating it as a possibility.
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,275 Posts
Re: p0300

If you've only got a p0300 code, then going to the parts store to get your codes checked won't help, because you've already checked your codes, and it's just p0300. Anybody else following the logic here?

I'd say Sub's on the money. P0300 is a vague code, and everything he mentioned should be checked. On Chrysler and Ford products, it is commonly a crankshaft or camshaft position sensor that has gone out, though if given a little time, they will usually set a code. Check sensor wiring to all the heavy hitters under the hood if Sub's advice doesn't get you an answer. Sometimes one will burn up, rub through, the clip will deteriorate, or if you did any other work recently, you may have disconnected one and reconnected, but just not quite tight enough.
==========================
If you've only got a p0300 code,
then going to the parts store to get your codes checked won't help,
because you've already checked your codes,
and it's just p0300.
Anybody else following the logic here?

NO -
because our built-in scanner will ONLY display P0300 for misfires -
it will NOT display the individual cylinder codes -
P0301 - P0302 - P0303 - P0304 etc -

once you discover WHICH cylinder is misfiring -
it is MUCH easier and faster to diagnose the cause -

sure beats checking "everything" - in my opinion -
 

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Registered
1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
Re: p0300

I wasn't aware of that Bass! I guess I was making the assumption that he got the codes with a standard code scanner. So the built-in will only give the most generic - had no clue about that. Well, you learn something new every day, if you're doing it right. Is it like that on every system? Like in the case of a transmission slipping, will it only give generic info? I'd love to learn more about this.
 

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Registered
1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
Joined
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567 Posts
Re: p0300

Sure, but the OP didn't say "I didn't use a code reader to get this information, which is vague. My car gave it to me." You implied it, but he still could have got the code from a code reader, and it's the only code he's pulling. So we still don't know that a code reader wasn't involved. I pull a LOT of p0300 codes every day - not a single customer has ever came in and said "My Cadillac told me I have a p0300." So this is all still news to me!

As far as what assuming does, I've been an ass as far back as I can remember. This might not have helped any, but it didn't really make things any worse either.

As stated previously though, I like to learn, so at the end of the day, I'm a slightly smarter ass than I was an hour ago. I call that a win!
 

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Master of the Dark Art of Diagnostics
2003 DHS - two-2002 DHS, 2003 SLS, 1995 Sedan DeVille, 1989 Coupe DeVille
Joined
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19,275 Posts
Re: p0300

I wasn't aware of that Bass! I guess I was making the assumption that he got the codes with a standard code scanner. So the built-in will only give the most generic - had no clue about that. Well, you learn something new every day, if you're doing it right. Is it like that on every system? Like in the case of a transmission slipping, will it only give generic info? I'd love to learn more about this.
==========================
I was making the assumption that he got the codes with a standard code scanner.
"we" have "trained" - or at least tried to train our noobs
to check for codes and post the results - ALONG WITH THE DEFINITIONS -
when ever something goes wrong -

I bet I have posted that 10,000 times from my list of "canned responses" -
so - it might be "safer" to assume that anyone -
except the newest of noobs - are using the built-in scanner -

----------------

So the built-in will only give the most generic -
as far as misfiring - YES -
our built in scanner will only DISPLAY P0300 -
but it will store the specific cylinder - if detected -

Is it like that on every system?
NO -
our built-in scanner will usually give BETTER/more complete results
than most cheap hand-held units -

in fact - a lot of hand-helds won't give much more than "P" codes -
 

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Administrator
2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
Joined
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68,481 Posts
Re: p0300

rat, Bookmark this link. It is used with the OBD-II onboard scanner systems built into the (Cadillac) cars from 1996 to about the end of 2005. Any of those several hundred codes will display in our systems except a specific cylinder misfire condition. Some handheld OBD-II readers will define P 030X, as will most parts store scan tools.

As always, please read the sticky posts at the top of any forum threads page. They're there for several reasons, and the "How to pull codes" sticky is pretty self-explanatory.

http://www.cadillacfaq.com/faq/answers/dtccode.html

Earlier OBD1 codes can be found in a Google seaerch - like "1994 cadillac obd1 diagnostic code list" or something similar.
 

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Registered
1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
I've never had a Northstar, so I've never really needed to know a whole lot about them. I've got the OBD1 stuff printed out and it rides with me in my glove box. I appreciate the info, guys. I will definitely share it with any friends who drive newer Cadillacs. And try to get them to join, of course.
 

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Super Moderator
2003 Deville Base
Joined
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4,819 Posts
rat, it is I who was guilty of assuming. as knowledgeable as you are i just assumed you knew that our built in code scanner didn't specify which cylinder was misfiring. My apologies.
 

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Registered
1992 Fleetwood S&S Hearse, 1993 Buick Roadmaster
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567 Posts
rat, it is I who was guilty of assuming. as knowledgeable as you are i just assumed you knew that our built in code scanner didn't specify which cylinder was misfiring. My apologies.
Hahaha, that's the nicest thing anybody ever said to me!!! lol

No, I'm definitely NOT that knowledgeable. There are a lot of limits to what I know, because I have to know a tiny bit about a lot of automotive stuff to do my job. So I never get to be the master of anything. Guys like Bass, Sub, and a few others here have a wealth of information that I'll never be able to touch. But, I don't want to sit on the sidelines just because I don't know as much as everyone else. I recently got a thank-you from a member because I recommended that he check his fuse because of a problem he was having. I honestly don't remember who it was. But he said thanks because he overlooked it. The way I see it, master mechanics send cars home every day with statements like "I can't find anything wrong" or "I couldn't make it act up like you described," and sometimes a loose connection, dead fuse, or some other insignificant stuff was overlooked. So, I chime in with my two cents, which I know is only worth two cents, but it's all I got! And I appreciate people like yourself, who complement me on the little I do know instead of telling me what I should know. You're good people!
 
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