hocuspocus

Followed the tutorial here, then searched for solution found nothing.

I attempted to reset my CEL by pulling back up fuse to no avail. Followed instructions first, then kept fuse out for 10min then 20min CEL never cleared.

Anyone have any idea why this is happening?

MM3Kwolik

You more than likely have a failed cat which took out your secondary O2 sensor with it. Since the sensor itself is damaged, simply turning the key will trigger the code again and again until the sensor is corrected.

notaloafer

X2. This happened to me in MY02. Constant CEL set when turning the car on - cat honeycomb had busted loose and took the o2 sensor with it.

hocuspocus

Thanks for the reply, I thought that could be the problem as well until I got the code cleared from a scanner. I just bought this car and it has a test pipe for now. I installed a spacer for the sensor before I tried to reset the code.

I wasnt sure if a broken sensor would trip immediately or not.(thanks for the info)
I drove for about 20min and it hasnt come one again yet, so I am assuming the o2 sensor works well enough not to immediately trip a CEL.

If anyone else can explain why, I couldn't clear code (in the case that the o2 sensor does work properly) or explain why clearing the code with a scanner has prevented the system from immediately tripping with a broken o2 sensor; I would greatly appreciate it.

Just looking to learn something, I don't plan on taking any action if the CEL doesn't trip again.

DeeKay

ECU logs cycles. The ecu is just a voltmeter, timer, and a filing cabinet. I'm not sure what the set parameters are, however ecu's set codes based on conditions. Conditions must be met for a code to set, each code has it's own conditions. A condition can be anything, 160deg operating temp, 2 ignition cycles, 5 faults within 30 seconds, no voltage at pin 6 for 10 seconds, any number of things.

For o2 sensors, although I don't know specifics, however there needs to be a duration of operation time for the code to set. The signal given to the ecu by the o2 sensor is compared with the other input information over a duration of time. If the conditions are met within that set time to set p0420 than the ecu tells cluster to put light on and a code is stored.

The best way to manually clear a code without a scanner is to disconnect the battery for 30 ish minutes (varying perspectives on this), or my favorite way, detach both terminals of battery and then connect the positive and negative battery cable together, completing a circuit (no battery) which will drain the capacitors in the ecu within 15 min, reattach to battery like normal and everything is reset.

By "everything" the only thing you are actually resetting by doing this is the KAM (keep-alive memory).

Utah S2K

Well said.....

Utah