well im not the one who tampered with it, the cat was already removed when i bought the Blazer all im trying to do is fix the exhaust leak. what im saying is if i just put a new straight pipe in and have it re-welded professionally will it then turn on the SES light? i cannot stand when any of my dash lights are on and will go to extremes to fix them and turn them off. if it does and the only way to fix it is to put a cat back on then i will do that too. i have no differing opinions either way. i realize its against the law, it creating more pollution for our atmosphere. and i also know dealers will not do anything with removing/flashing anything with PCM. i was only looking for suggestions on fixing my bad exhaust leak where the cat was from poor welding of the straight pipe. thats it

 

It doesn't matter who tampered with it. What matters is that your name is on the title/registration, which means it's your responsibility to prove you didn't do it. It ends up being a real mess tracking ownership back and trying to prove who owned it when it was tampered with. If it can't be traced back, or you can't prove that you didn't do it, you're on the hook for the fine, and installing a converter. You can avoid a huge headache just by installing a converter.

As for the SES light, without a converter, it will come on, unless the PCM has been tampered with, (the PCM is considered an emission control device).

As for the exhaust leak, check around with local muffler shops, but don't be surprised if they won't do it. They know the law, and trust me, they certainly don't want to be liable for a $3500 fine.

Bottom line: Best to fix it properly and be done with it.

 

the light is not on i do not know how. so lets say i put a cat back on, if the PCM was tampered with (not by me) with the cat back in place. would i get a "check engine"? i have no scan tools to check to see if anything has been done to the PCM, and if i take it in to get checked out and they find it was am i screwed? i will probably put a catalytic convertor back on but i have no welding tool or exp. so i wont be doing it

 

The PCM monitors several circuits continuously for failures, (TPS, MAP, MAF, ECT, CPS, CMP, IAT, etc etc). It does not continuously monitor the oxygen sensors for failures. The PCM runs the O2 sensor monitor, (test) only under certain circumstances while driving. This explains what has to happen: General Motors Driving Cycle If the drive cycle is not duplicated exactly as written, the monitor will be incomplete. If the monitor is incomplete, the SES light will not come on even though there might be a problem. This is why it can take a while for the SES light to come on after clearing the memory. If the monitor runs and completes its test and a failure is detected, the SES light comes on and a DTC is set in memory. You can see if all monitors have run and completed their tests by using a scan tool. Most auto parts stores will retrieve DTC's and check monitor status for free.

With regards to your question: "so lets say i put a cat back on, if the PCM was tampered with (not by me) with the cat back in place would i get a "check engine"?"

The answer is a definite "who knows" The known problems must be taken care of first. Then clear the memories, perform a drive cycle, make sure all monitors have run and completed, and let the PCM do its thing. It will tell you if there's a problem by turning the SES light on.