bradpsu

300 code and service engine soon light on 2003 Seville SLS

Recommended Posts

My 2003 Seville SLS has had an ongoing issue with a p300 code for multiple misfires.  Problem is there is no issue with the engine running roughly in any way.  Plugs have been replaced, a coil pack has been replaced and it still comes back.  It only occurs when driving on the highway at speed and the service engine soon light comes on pretty quickly (within a few miles of driving now....it used to take longer drives for it to come on).  It's flashing at times only to go out and then flash again.  Eventually the light comes on and stays on (not flashing).  I'm wondering if this is a catalytic converter issue since short drives around town do not cause the light to ever come on.  

My car has mid 80,000 and I'm wondering if it is a converter issue could it just have gone bad or could there be an issue with the fuel injectors causing the converter to fail by possibly passing un-burnt fuel into the converter.  

 

Any help would be greatly appreciated.

 

Brad in Pa

Share this post


Link to post
Share on other sites

Is P0300 the only code?  List them all if P0300 is not the only one.

Since it is a random misfire it is possible it is a vacuum leak or other related lean condition.


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites

Multiple misfire is the only code.  Was wondering if anyone else had come across this issue.  Most all of the same code conversation I've read about has been related to a stumbling or rough running engine.  Mine is fine in that regard.  

 

And it's not really random......all I need to do is hit the highway, get it up to 60 or so and in about 5 minutes or less the service engine soon light will come on steady or flash.  And to be clear when it does there is nothing noticeable at all about the performance of the engine being off.  I will say that a recent round trip from York to Baltimore seemed to use more fuel than normal.  This is why I thought it could likely be a cat converter issue.....knowing that fuel mileage decline is a sign of such an issue.   

Share this post


Link to post
Share on other sites

On a 2003.....all you get is po300. There is no such thing as po301-308 code in the service manual. You need a Tech2 to display a graph to show which cylinder is misfiring.

Some claim a few higher cost aftermarket scan tools can display which cylinder is misfiring....but I've never seen it done.

Without a scan tool that can show which cylinder(s) is/are missing....your just guessing.

A flashing SES lamp indicates a misfire bad enough to damage the catalytic converters.

tech2 graph.jpg

Share this post


Link to post
Share on other sites

My decent code reader states what cylinder is missing.

I would not be surprised if the other coil assembly was bad. They were very common to getting heat cracks and intermittently failing.

I dont recommend putting a used coil unit but rather a new oe unit

also there may be oil filled in one or more of the plug wells causing issues as well. 

If there is I would replace the boot


GM FAN FOREVER

Nice, clean, luxury= fine automobile

Share this post


Link to post
Share on other sites

Most scan tools will not show which cylinder is missing on a 2000-2003 Northstar. 

I have a hand full of scan tools here.....only the Tech 2 will show which cylinder on a 2000-2003 Northstar. 

Technically.....There is no such thing as a PO301-PO308 code in the GM service manual for a 2000-2003 Northstar. Show me the manual that does. 

If a scan tool shows it....it's reversed engineered to do so. 

Be aware....this applies to 2000-2003 models only. You are just chasing your tail if you don't know which cylinder. 

 

Share this post


Link to post
Share on other sites
4 hours ago, Logan said:

Most scan tools will not show which cylinder is missing on a 2000-2003 Northstar.

Hmmm,

I was thinking my Snap-on scanner gave misfire counts by cylinder on Cadillac too,  BUT I'm remembering last time I accessed mis-fire data it was on the 2005 GMC. Snap-on advertisements even show live mis-fire data on a 2004 chevy 

Logan, was there a proprietary software access problem with only 2000-2003 Cadillac?

If I get time between rain squalls I may hook up the Snap-on scanner to the 02 Seville...

4 hours ago, Logan said:

You are just chasing your tail if you don't know which cylinder

Very true statement. :scenic: Also, even though you may not feel it miss, the computer can still "detect" it. The PCM breaks it down in fractions of a second. The MIL will flash until the catalyst damaging condition is no longer present THEN the MIL will stay on steady. If the catalyst damaging misfires exceed 2 the PCM will disable TCC.

Have someone with a Tech 2 scan it and verify which cylinder or cylinders is causing the code.

5 hours ago, rockfangd said:

I would not be surprised if the other coil assembly was bad. They were very common to getting heat cracks and intermittently failing.

Wouldn't surprise me either..

@Logan even the 98 FSM doesn't break it down per cylinder any more, only has the P0300 misfire detected..( Sorry my bad ) :blush:

 

 

Edited by OldCadTech

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites
7 hours ago, bradpsu said:

This is why I thought it could likely be a cat converter issue.....knowing that fuel mileage decline is a sign of such an issue.   

The catalytic converter does not cause poor fuel mileage. Catalytic converter damage results from rich fuel mixtures, which is poor fuel mileage. If the cat is subjected to rich fuel/air mixtures long enough they will clog and restrict the exhaust, requiring catalytic converter replacement.


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites

2000-2003 Northstar engine. 

There is no such thing as a code PO301-PO308 on a 2000-2003 Northstar. Go look that up in the GM service manual.

The onboard diagnostics will only show PO300. You will not be able to tell which cylinder is missing. 

You will need a scan tool that can display the cylinder misfires. Most cannot. 

Most people don't have a Snap On tool sitting around. 

Share this post


Link to post
Share on other sites

my 01 eldo had issues with misfires and I pulled the cylinder code. 

The tool I used was Innova 3100. Like that one anyway but a little older model. It works nicely for ecm and abs. and it shows monitor status


GM FAN FOREVER

Nice, clean, luxury= fine automobile

Share this post


Link to post
Share on other sites
11 hours ago, OldCadTech said:

@Logan even the 98 FSM doesn't break it down per cylinder any more, only has the P0300 misfire detected..( Sorry my bad )

7 hours ago, Logan said:

There is no such thing as a code PO301-PO308 on a 2000-2003 Northstar. Go look that up in the GM service manual.

 

 

 


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites

It's never been there....just po300. 

So anyway.....now what? Guy has a po300 code and no way to detect which cylinder. There must be a obvious misfire because the SES lamp is flashing. 

He could go to Auto Zone....but they would just try to sell him a O2 sensor. 

 

po300.JPG

Share this post


Link to post
Share on other sites

I suggest he spend the diag time to have it scanned with a Tech 2. 


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites

While I greatly appreciate all the advice on tech tools (none of which I have) I'm really just trying to see if anyone out there has had or heard of a similar experience and what was done to fix it.  It's been really frustrating.  I don't feel comfortable driving anything is excess of short trips around town for fear of causing more damage.  As stated before, it frustrating because the engine is running fine by all accounts.  I had a rusted coil pack replaced and while the other one also had some rust on it, it was not as bad and was cleaned up.  My mechanic and I debated changing the 2nd coil pack but even he said with the way the engine is running (pretty smoothly) it could just be a waste of money and the issue would likely persist.  

 

I'm shooting somewhat in the dark here but I'm wondering if I've got some fuel injector issues......have dumped a bottle and a half now of Lucas Oil F.I. cleaner into my tank as one more thing to try.  I'm concerned that the Catalytic converter may already have been somewhat damaged.......I know when they heat up and get going say in highway driving and there is an issue that's where it will show up with the SES lights, steady or flashing.  And that's what I get as soon as I get out on the highway and get it up to speed for 5 minutes or so.  

 

Not being a mechanic excuse the dumb question.......on this duel exhaust Northstar, are there two or just one C.C?  And if they do need replaced can they be replaced without replacing the entire exhaust system?  I don't remember if they are removable for "easy" replacement or if they are welded right into the exhaust pipes.  

 

Back to the codes and tech tools....my mechanic states that on my 2003 Seville the multiple misfire codes don't have the capability of being more specific as to which cylinders are having issues.  He stated it's probably best to take it to my Caddy dealer to have them listen to each cylinder and try and see if one or more issues can actually be detected.  I was wondering if anyone here had a C.Converter issue (with no apparent misfires) that caused the SES light to come on steady or flash...or both.  

 

I'm trying to get my ducks in a row best I can and keep the costs down on this car that I do love......but dumping endless cash into it trying to randomly see if that fixes the issue doesn't seem like that's a road I'd like to continue down.  

 

Thanks again for all the feedback.

 

Brad

Share this post


Link to post
Share on other sites
On 11/9/2017 at 11:40 PM, OldCadTech said:
On 11/9/2017 at 7:38 PM, Logan said:

You are just chasing your tail if you don't know which cylinder

Very true statement. :scenic: Also, even though you may not feel it miss, the computer can still "detect" it. The PCM breaks it down in fractions of a second. The MIL will flash until the catalyst damaging condition is no longer present THEN the MIL will stay on steady. If the catalyst damaging misfires exceed 2 the PCM will disable TCC.

Have someone with a Tech 2 scan it and verify which cylinder or cylinders is causing the code.

 

On 11/10/2017 at 12:10 AM, OldCadTech said:

The catalytic converter does not cause poor fuel mileage. Catalytic converter damage results from rich fuel mixtures, which is poor fuel mileage. If the cat is subjected to rich fuel/air mixtures long enough they will clog and restrict the exhaust, requiring catalytic converter replacement.

 

On 11/10/2017 at 1:16 PM, OldCadTech said:

I suggest he spend the diag time to have it scanned with a Tech 2

 


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites
On 11/9/2017 at 11:40 PM, OldCadTech said:
On 11/9/2017 at 7:20 PM, rockfangd said:

I would not be surprised if the other coil assembly was bad. They were very common to getting heat cracks and intermittently failing.

Wouldn't surprise me either..

 


THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

Share this post


Link to post
Share on other sites
15 hours ago, bradpsu said:

Back to the codes and tech tools....my mechanic states that on my 2003 Seville the multiple misfire codes don't have the capability of being more specific as to which cylinders are having issues.  He stated it's probably best to take it to my Caddy dealer to have them listen to each cylinder and try and see if one or more issues can actually be detected.  I was wondering if anyone here had a C.Converter issue (with no apparent misfires) that caused the SES light to come on steady or flash...or both.  

 

Most of this post has been a discussion about that. 

Few scan tools can show which cylinder is the misfiring one.  But without one that can show which cylinder....You are adrift at sea...

A GM Tech 2 can show the misfiring cylinder no problem. 

It sounds like your mechanic does not have a good enough scan tool to show the missing cylinder. He is right about sending you to the dealer. They will have a GM Tech 2.

They may have to drive it 20-30 minutes to see it.....some onesees and twosees are normal......but here in this case... It's obvious that cylinder #2 needs a closer look. This 2009 Chevy had a random miss under speed and load......no codes (not even po300). A new coil fixed this one. 

 

gmtech2#2.jpg

Share this post


Link to post
Share on other sites

Just because the towers on the coil packs dont have rust, or have minimal rust doesnt mean they are fine.

If this were my car I would get it properly diagnosed for the miss and very likely replace the other coil pack.

Any cracking in the coil pack and I replace them. 

My eldo had issues like you describe and once I replaced both coils it ran like new. Most times I thought it was running fine when the light came on but once they were replaced it purred. Both were bad. 

1 is grey, 1 is black. But both are interchangeable. 

spend a little and get the proper codes, that will greatly help you. 

As for injector issue... Rarely do I have any issues, not saying it is not possible, but maybe less likely 


GM FAN FOREVER

Nice, clean, luxury= fine automobile

Share this post


Link to post
Share on other sites

Thanks for the feedback rockfangd.  I held off on the other coil pack replacement because my bill was a little steep at the time and I had them replace the one that looked the worst rust wise which the service adviser suggested.  Maybe I should try the other one now.   

I'll be taking it down to my Caddy dealer to properly diagnose the issue before replacing the other pack but let me ask a question of you and the group here.  Knowing that head gaskets are notorious on these Northstar engines, could a HG that is going bad cause a 300 code and the subsequent SES warning light to come on?  

Edited by bradpsu
additional info needed

Share this post


Link to post
Share on other sites

Every aluminum block engine ever built will have some with pulled head bolts. 

Google 'Toyota Camry 2.4L head bolts'. 

The 2003 Northstar still used a M11 x 1.5 head bolt. 2004 went to a M11 x 2.0 bolt. 

I think most with leaking head bolts would have a misfire at initial cold start up and poor temperature control once warmed up. 

Don't be surprised if the service department suggests it is a head gasket and what you really need is a new Cadillac. They do it all the time.

 

Share this post


Link to post
Share on other sites

I never have a SES light come on at start up and temp control seems fine.  Only time SES light comes on is once I'm at highway speeds after about 5-10 minutes of driving.......sometimes flashing and sometimes steady.

I'm aware that a Caddy service center will likely go to the HG being bad and onto "why pay all that money....just buy a new Caddy?"  That's not an option for me...ha!  

Let me ask what may be a stupid question on these pulled head bolts.  Are they an easier fix then replacing a head gasket?  And most importantly a significantly cheaper fix?  

Share this post


Link to post
Share on other sites

Nope....it's a bunch of work to fix a bad / pulled head bolt thread...the cylinder head and head gasket would have to be removed.

Most 4 cylinder cars a Time Sert repair kit can be used with the engine in the car. The Northstar engine pretty much has to be removed to use a Time Sert kit.

Chances are your coil pack is getting goofy as it gets warmed up. But this needs to be verified...kinda the only way is to test it with a GM Tech 2.....or just buy a new coil and try it.

I used to carry a tested spare coil in my trunk.

Share this post


Link to post
Share on other sites

Just an fyi to all on this issue........my Caddy service man finally diagnosed the issue on my Seville.  Excess carbon build up was the issue.  As it would heat up at highway speeds the carbon would start to break up and circulate causing multiple misfires.  This is a product of in part ethanol issues and not driving the Seville enough at speed to blow off built up carbon deposits.  

 

He put in a cleaner that soaks in the crank case for 2 hours and then they start the engine to blow out the dissolved carbon.  It seems to have worked like a charm....no more SES lights at all under any driving conditions.  Running smoother as well.  I was really worrying that it was a head gasket but they were sure it wasn't and convinced me to try this carbon cleaning.  

 

Anyways.....wanted to make all aware that may be having the issues I was having.  With all the diagnosis time (which took nearly 3 days) and the cleaning (which of course requires an oil change after) total bill was $500.00.  Not cheap but a hell of lot cheaper than replacing a head gasket!  

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.