# Check Engine Light



## 04YJ-GTO (Nov 7, 2007)

I have an 04 GTO with LTs and high flow cats. The check engine light keeps coming on b/c of the factory o2 sensors with the high flow cats. How do I solve this problem? They don't make o2 simulators anymore(illegal). Are there performance o2 censors for aftermarket cats? Hopefully someone can help me.


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## cncmasterofor (Jan 19, 2008)

Need to get her tuned. Predator worked for me. You can go handheld or not.


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## 04YJ-GTO (Nov 7, 2007)

cncmasterofor said:


> Need to get her tuned. Predator worked for me. You can go handheld or not.


yep, thats what the speed shop told me, just tryen to see if there was another way


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## Tri-Power (Jan 10, 2008)

well, you could always make your own 02 sensor sims, there are write-ups floating around on various sites, and i've helped a few of my friends do it for their Jeeps. they aren't too bad.


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## Rukee (Feb 8, 2007)

couldn`t you just drill a hole in end of the new cats and weld in bungs for a O2 sensors?


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## Chrisco (Mar 19, 2007)

Rukee said:


> couldn`t you just drill a hole in end of the new cats and weld in bungs for a O2 sensors?


Most high flow cats have an O2 bung in them. The reason the check engine light is on is because the high flow cat doesn't "filter" as much as the stocker did and therefore the O2 sensor is getting a different reading and setting the check engine light.


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## Rukee (Feb 8, 2007)

You would think there would be an O2 sensor made that has the values the computer needs.


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## Chrisco (Mar 19, 2007)

Rukee said:


> You would think there would be an O2 sensor made that has the values the computer needs.


I imagine that could be done. Recalibrating one might work. But for the time and effort, it's just better to tune it out.


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## Rukee (Feb 8, 2007)

If a guy knew the values they send for all the O2 sensors made, then you could just pick the one with the right values. O2 sensor DATA base is what we need.


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## 04YJ-GTO (Nov 7, 2007)

If I have to go to a speed shop and have her tuned for that, I'm just gonna wait and buy a cam, maybe even a set of heads too


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## Chrisco (Mar 19, 2007)

Rukee said:


> If a guy knew the values they send for all the O2 sensors made, then you could just pick the one with the right values. O2 sensor DATA base is what we need.


That makes sense. If there's an O2 sensor that reads how much oxygen is in your exhaust after your cats and sends the right signal to the PCM then your problem is solved. In other words, you'd have to find an O2 sensor that sees how much oxygen is in the exhaust and take that reading and send the same signal as the stock one did with stock cats.


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## Rukee (Feb 8, 2007)

yea, even if a guy needed to change out the plug-in on the end of the wires, as long as it`s sending values within the perimeters of the ECM, you should be good to go. Would be sweet to figure it out and be able to say buy an O2 sensor for such-and-such car, swap the ends and plug it in. :cheers:


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## Chrisco (Mar 19, 2007)

Rukee said:


> yea, even if a guy needed to change out the plug-in on the end of the wires, as long as it`s sending values within the perimeters of the ECM, you should be good to go. Would be sweet to figure it out and be able to say buy an O2 sensor for such-and-such car, swap the ends and plug it in. :cheers:


Yeah it would be pretty sweet. Usually people get a tune when they do headers though and they could just have the code tuned out on the dyno.


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## Rukee (Feb 8, 2007)

Eliminating the code is not the answer is it?? Doesn`t the ECM use those O2 sensors and their values to tune the engine itself? If whatever was needed... faster responding; running in a different temp range; offset values from stock, whatever it is is fixed, then the ECM could do it`s thing. I`m reading threads saying doing the delete code causes excess rich smelling exhaust. Speculating here but perhaps having working O2 sensors would cure that, increase power, throttle response and fuel economy.


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## Chrisco (Mar 19, 2007)

Rukee said:


> Eliminating the code is not the answer is it?? Doesn`t the ECM use those O2 sensors and their values to tune the engine itself? If whatever was needed... faster responding; running in a different temp range; offset values from stock, whatever it is is fixed, then the ECM could do it`s thing. I`m reading threads saying doing the delete code causes excess rich smelling exhaust. Speculating here but perhaps having working O2 sensors would cure that, increase power, throttle response and fuel economy.


We're talking rear O2 sensors here. The ECM uses the front O2 sensors only for fuel adjustment. The rear O2's are just a sanity check to see if the cats are working and have no effect whatsoever on performance.


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## SloTymer (Sep 16, 2005)

When I put my LT's w/Hi flow cats on, it didn't mess up anything. Everything is as it ever was. Lucky me for once. arty:


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## Rukee (Feb 8, 2007)

Chrisco said:


> We're talking rear O2 sensors here. The ECM uses the front O2 sensors only for fuel adjustment. The rear O2's are just a sanity check to see if the cats are working and have no effect whatsoever on performance.


In that case I wouldn`t feel bad about eliminating the code.


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