Wasatch Rebel

When my check engine light came on a couple of months ago, I ran the code and now I can't remember what it was, but several people told me that it was probably my front O2 sensor...so I changed that pulled off the thing in the fuse box that you're supposed to pull off to reset thing (ECU?), and left that off for about an hour. When I put things back together and drove it around, the check engine light was still on. It stayed on for a few days, but now has gone off. Prior to changing the sensor, I had also cleaned the MAF in an attempt to clear things up, but the light had stayed on.

Anyway, my light during this time has gone off for a couple of days, only to come back on several times. I'm wondering if this is normal if I haven't fixed the problem, or if the problem was unfixed, wouldn't the check engine light just stay on until it was?

MudHippy

What year? Engine?

There's only one O2 sensor if it's an 86-95. And it's got an AFM not a MAF. Those things in the fuse box are called fuses. Unless you pulled the EFI main relay in the fuse box under the hood instead of pulling the EFI fuse in the fuse box by the driver's side kick panel in the cab. Which it sounds like you did, if the check engine light never went out.

If the check engine light has come on at all after going out, then there's still a problem.

Go check the codes and report back what one(s) is present. You'll have atleast one still stored if you never actually reset it.

thook

All you have to do to reset the diagnostic memory of the ECU is disconnect power supply to it. It's just like resetting the radio memory for your pretuned stations and what not. This, for the ECU, can be done by disconnecting the battery or the EFI 15amp fuse in under the hood.

If this was done correctly, then it could only mean the ECU is detecting the real problem once again and only signaling the error when the condition is present. The code will never go away permanently until it's fixed. It will remain stored. This is because whatever electrical component is having a fit is part of the entire EFI circuit system in which the ECU is connected to in everyway.....though OBD1 does have several limitations.

Anyway, it's pointless to try and fix anything until you know what the code is. And, if it's still an O2 code, it doesn't mean there's a problem with the sensor.

CA emissions models have two after a certain year. Not sure which year starting, but atleast from '91 to '95.

Wasatch Rebel

Doggone it, I posted in the wrong section. Sorry. I have a 2000 4runner 6 cylinder. I don't have my own code tester, so I'll need to stop by Autozone to get the code run. I pulled the EFI from the fuse box under the hood. The code I originally got was P0171. Someone on another forum (I think) told me the most likely culprit was the front O2 sensor. I took a look at it and it looked like it had seen a lot of miles and that it wouldn't hurt to put a new one on, so I pulled the EFI, then changed the sensor, the plugged the EFI back in. The check engine light was on for 2-3 days after that, and then one morning I went out to start it up and the check engine light was no longer on. It's been 3 days since it went off and it hasn't been back on. So could it have taken a couple of days for the new oxygen sensor to be recognized by the system?

thook

No. It'd be recognized right away. More likely, it took a couple of days and a bit of driving around for the a/f ratio to balance out due to the new sensor and the ECU being able to correct the a/f ratio better.

thralldad

http://www.youtube.com/watch?v=sXXs-MK7u-0

Google is your friend.

Wasatch Rebel

Thanks. That's some weight off my mind.

RMP8080

California Truck?