so 2 weeks ago the chk engine light came on and i pulled the fuse to reset it to see if it was a fluke or an actual problem, the light didnt come back on. then this morning when i was on my way to work it came on again so i took it to autozone to get the code read and they said there was no power to my port, so i checked litterally every fuse one by one on the side dash and under the hood and they were all fine, then i hit the port with a test light and it lights right up, so the port has power but cannot be read, what would cause this to happen?

Did you check the correct pin? Do you have a good ground? DO you actually trust the Auto Zone generic scanner to give you the correct code?

well there is 4 pins in it, 3 on top and one on bottom right side the one on the bottom right is the one that is showing as having power, and i grounded to the door frame so the ground is good, and maybe it could be the autozone scanner, ill try checker later today

seems it was their pos scanner, the one at checkers worked perfectly fine...code p0420 bad o2 sensor, i think i may have exhaust leak instead, just put on header about 2 months ago

P0420 is a catalyst low efficiency code. Could be an exhaust leak, bad O2 sensor (post cat), damaged wire, or even a bad Cat. Best bet is to use a good scanner and actually watch the readings. There is a reason I wont sell my Tech II even though I have had offers (close to what I paid for it, but way less than its real value).

well i went through and did another round on all the header bolts, got maybe a half turn more out of a few of them, hopefully that keeps it from coming back, pretty sure its not the cat, replaced it with a magnaflow when i put on the header. and if it is the o2 sensor at least iyts the one after the cat cause that will b easy as hell to replace compared to the one cramped up on the header

I have been through three maganflows. Finally gave up on them.

the cat should be good, magnaflow is a trusted veteran in auto industry, the header bolts may be loose, or the connecton to the downpipe, but if that 0420 code is lit reguagdless of what scanner you use its a standard that means a code will show reguardless of the quality of the scanner, less the scanner is busted(autozone's) because it was abused in some way, in my dealings with 0420 code on several different vehicles replace the o2 sensor after the cat and she should go away for you, if not it could be because the car is running too good and is out of spec with the headers and high flow cat especially if the exhaust is 2 and a half inch from cat to can, and if you have an intake system as well, my z24 does it, but there is nothing wrong with it passes emissions and gets an easy 26+mpg average

HDRacing wrote:the cat should be good, magnaflow is a trusted veteran in auto industry, the header bolts may be loose, or the connecton to the downpipe, but if that 0420 code is lit reguagdless of what scanner you use its a standard that means a code will show reguardless of the quality of the scanner, less the scanner is busted(autozone's) because it was abused in some way, in my dealings with 0420 code on several different vehicles replace the o2 sensor after the cat and she should go away for you, if not it could be because the car is running too good and is out of spec with the headers and high flow cat especially if the exhaust is 2 and a half inch from cat to can, and if you have an intake system as well, my z24 does it, but there is nothing wrong with it passes emissions and gets an easy 26+mpg average

Many aftermarket scanners DO give wrong code numbers. As someone that used to have to deal with this in a dealer I am well aware of the false information Auto Zone scanners give out. P0420 is a Catalyslt low efficiency code, the vast majority of cars I have worked on with just that code in them have needed a new catalytic converter. Magnaflow may be a trusted name, but after having three of them fail I will never buy another if I can avoid it.

well after doing a round on ALL the bolts on the exhaust the code came back yesterday...so im stuck to it either being my new cat, or the o2 sensor which had no problems till right after i did the exhaust

That code could also mean that you engine is not running efficiently enough for the cat to completely remove all the pollutants coming to it.

Dan