Looking at an 01 TT which current owner says is getting a CEL every couple hundred miles. It has an aftermarket exhaust as well as a flash. Is there a typical cause of CEL based on exhaust? Is there a way around it? I'll try to get some additional information as to particular codes and exhaust type (claims it is a $5000 exhaust!). Must have paid extra for the CEL code generator.

Thanks.

 

It can happen with high flow cats, though most flashes can be setup to eliminate the issue.

 

CEL is caused by catalytics that aren't as efficient. OBD-II emission systems check that effeciency so if he's got a bad catalytic or a really high flow catalytic that doesn't work as effeciently as the emission system expects it will pop a CEL....

 

So I assume this is something that is measured by the O2 sensors after the cats and finding two much of a particular gas throws a code. If I can get the codes would that indicate what the particular problem?

What is meant by the comment that it can be corrected with a flash? This sounds like a workaround of the problem. Would this then pass the normal state inspections?

 

We turn off the post cat 02s and the cel never comes on.. many 100 cell cats eventually will throw a code... but that also may have something to do with lazy 02s...

 

So does the Post CAT O2 sensor effect driveability or is it just an exhaust gas measurement? Will it still pass the inspection process with it off?

Thanks.

 

With out programming it stays is readiness mode so it passes. We do this for the catless exhaust too.

 

It will also pass an OBD-II plug-in inspection

 

You can simply get 02 spacer bungs for the secondary sensors. It's literally just a threaded spacer. No more CEL, CAT or not...

 

Why is everyone talking about cats, codes and flashing?!?!?

A "seller" has tried to explain a spurious CEL to a buyer, and has claimed it must be the exhaust.

WHO KNOWS????

I think giving the OP any advice other that "get the codes, get it diagnosed before you purchase" is misleading.

IMHO

A

 

I'm sorry but I found this part of the opening post pretty informative as to intent, did you not? -> " Is there a typical cause of CEL based on exhaust? Is there a way around it?"

 

If this is a post catalytic O2 code no it will not effect driveability. It will pass inspection in most states only if the CEL is not lit, simply resetting it will not be good enough generally. the computer reports when it was last reset and will require a certai nnumber of miles or perhaps drive cycles before it reports "ready" and can be tested via plug-in as they do in my state. This is done specifically to prevent people from resetting the codes and then going straight to test. If you flash the car to ignore the secondary O2s then even catless it would pass the plug-in test but obviously not a sniffer. Many states to speed up emissions testing, especially on AWD cars, skip the dyno test and go for either a static RPM sniffer test or a plug-in test. With high flow cats you MAY pass a static RPM and idle test fine so long as they are functioning correctly. If they simply do a plug-in then the computer reports all is well if that programming is installed Do you know who flashed the car? Getting the specific code read and reported back here would obviously be a good idea but this sounds like the typical secondary O2 that can come from high flow low cell count catalytics and could be fixed with a flash - just brace yourself for the cost of a flash.

 

I'll bite:

Which aftermarket exhausts cause CELs? (other than straight pipes and cat deletes)...Be good to list those.

Everyone has concentrated on the "way around it" while it has not been established that his CELs are exhaust related CELs. Sure he asked, but I'd like to think we can make sure the OP gets the actual problem addressed, not just what he thinks may be the problem.

OP What kind of flash is on the car? And of course you need to get the codes from those CELs, not just what the seller said they were.

A

 

Totally agree. CEL can be many other issues besides an aftermarket exhaust. Get it checked out. Even if it just the aftermarket exhaust, will you be able to pass smog in your state? At a minimum get the stock exhaust just in case.

 

Great responses guys. I will definitely verify the actual codes that were generated before doing anything. Thanks.