I got a custom exhaust system put on my Lancer from the flex pipe back in December. They wanted $80 to drill a hole and weld a nut for the O2 sensor so i had them just set it aside and I figured I would do it my self. Well it hasn't sent a code (I have a mac scanner and have checked a couple of times). I was wondering if my car has a programing flaw or if someone else has run into this also.

 

i have unhooked my second 02 sensor a couple of times but my car has always thrown a code b/c of it. It really should throw a code without that sensor.

 

It will probably take time before your ECU will finally wake up and throw a code.

 

if its the rear O2 then it might not throw a code at first, but it will eventually. the car only takes readings from the second sensor periodically, unlike like the first one where it reads every time u turn on the car

 

The sensor isn't unhooked it's out of the exhaust stream laying on a brace. I have hooked the scan tool up to it and it says all tests run. I cleared codes (reseting tests,and ECU) and have re-run the test. All passed. The second O2 has run it's check. Still no light 3 months later.

 

Try to reset the ECU and see if gives the CEL. running without 02 censor might create huge problems in future......correct me if i m wrong.

 

My thinking is the computer has a upper limit on the voltage aka running rich/bad cat, but has no lower limit. As far as the computer is concerned the cat is doing a perfect job. Reading pure O2. I was wondering if others have found this if not maybe someone else could try it. If it's not just a flaw on my Lancer but a factory program loop then nobody would need a CEL eliminator, or have to worry about the CEL light when installing a header.

 

The second O2 only checks if the cat is operating. Running with out it will cause no problems. Running with out the first O2 would cause you to run in open loop killing your performance.

 

still running without the o2 inline still no problems!

 

U must be special.