So since I'm back using the OBD2A Ecu for my LS Integra... I was debating on buying a 555 timer and making my own secondary O2 sim.. But then I got to thinking...why doesn't anyone ever just wire the primary O2 to the secondary O2? As far as I know they'd be providing the same signal to the ECU. Has anyone tried this?

 

Wiring both together would make the ECU think that the cat wasn't working, and throw a CEL.

The 2nd O2 needs to read differently (forget which direction, more or less voltage) to know that the cat is still operational. The 1st (primary) is used to control the mixture and such, the 2nd is just to check on the cat.

 

You're right, and now that I think about it... I believe the 2nd O2 sends something like 0v and 0.9v in specific intervals so that the ecu knows the cat is working. Correct me if I'm wrong

 

Try this. Worked for me.

http://forums.evolutionm.net/evo-how...cel-light.html

 

^^^ that method works for pretty much any car. But you're at the mercy of the life of the O2.

555 circuit stuck inside the ECU works forever.