Pre-cat O2 sensor....is it really needed?

[SuperRunner]

For my 1UZ swap, I did not include the pre-cat O2 sensor. I have done other swaps that had pre-cat sensors, but they were not required by the ECU to pass the sniffer test.

Here is my problem. I just failed the idle test. CO2 was great, but the hydrocarbons were too high. 550 is what I read, and it should be 220.

It passed just fine on the high idle test.

These tests were NOT done on a dyno, as that is not required in my county.

Does the 1UZ require that pre-cat sensor or should it be able to pass without it?

 

[speeed_dmonx]

precat sensor

hey SuperRunner;
the first 2 pre-cats(or 1 pre cat) is for engine control of fuel and air mixture the second 'AFTER CAT' is for the computer to verify that the CAT is working fine and so it does not trip a code...I have a GMC that I hopped up a vortec 350 and it had 4 sensors...2 before and 2 after...the ones before are the most important..the ones after in the case of the GMC I just bought special blockoffs(resistors) since if they are not plugged in they throw a code saying something is wrong and make the motor run like crapola...now....I am willing to bet since Toyota and Chevy are very similiar that this is the case...everything follows logic toa certain degree...hope this helps

 

[Nick M]

Yep, Toyota uses the front sensor to keep the cat warm, the back is to make sure the cat is working.

They are the same logic on all US cars.

 

[SuperRunner]

but is it required to pass the sniffer test. I failed at idle but passed at higher RPM.