Riddle me this, tech heads.

[Joe 1320]

OBDII vehicle, had a bad cat and was tripping the SES light for a secondary 02 sensor catalyst effeciency. Cat had just started to break apart and rattle. A straight pipe was put in place and problem solved. Rear O2 sensor plugged back into the proper place on the pipe. Everything works great Except.......

No SES light. been driving it for days and that SES light should light up without the cat. I was planning on picking up an 02 sim, but now I'm mystified as why no SES light. It's not burned out, I can force it by disconnecting other stuff to trigger it.

any ideas as to why?

[Trash man]

its just checking against the pre cat sensor, it just monitors the air mixture coming out.

[Joe 1320]

its just checking against the pre cat sensor, it just monitors the air mixture coming out.

correct. but without a cat, there is not a difference between the pre-cat and after cat readings .....so every time that I've seen, it will set a code.

[Al 96 Ram Air T/A]

I'm assuming the bad cat that was removed is the same bank sensor correct? Another words...there's two cats, and four O2 sensors.......


But, the only other thing that comes to mind is = perhaps the pre sensor is not reading properly? If it reads different from the post sensor, I think OBD2 will allow it to pass. Simply because it different. So, if the pre sensor reads very high, even without a cat, the post sensor might be lower hence no code.

That's sounds crazy...but nothing else makes sense. You didn't have the rear sensors removed from the ECM code, right? I do not have any, since I converted from a two-cat OBD2 system to a single hi-flow cat OBD2 system. I deleted both post sensors for ease.

I'm confused on this one Joe....

[Trash man]

ive been thinking of this and its got me stumped, maybe when the cat was going bad, it was actually making one of the moniter gases worse, and now that the straight pipe is in, the post is reading a lower level that is within range?

[Wild Willy]

If it works, don't mess with it- take a high-temp pen and write "super-duper catalyst" on the straight pipe (we used to call them test tubes) so it could theoretically pass a visual emissions test, and drive it. I don't know if it was size or weight constraints, but the 4th gen Camaros seemed to have more than their share of catalyst problems. Both of mine were replaced before 100 k miles. GM actually had a silent recall, or some sort of adjustment, because the emission hardware is legally required to go 10 yr/100 k miles. Probably the same reason they used the platinum plugs, to last beyond the emission warranty period.

[ConElite]

That is a good one. Another thing you can so if it does come on instead of spending money on sims is a spark plug defouler. Works like a charm even without cats.

You only need to run one, not to like this pic.

[Christopherrr]

Was the downstream sensor relocated or as the bung extended? That's a rather obvious question you'd already know the answer to Joe...I'm stumped.