[UPDATE]

So I replaced the sensor, light came back on after about 40 miles of driving. So much for my mechanic's diagnosis that it was definitely a bad sensor.

But now after reading everything I can find online about this I'm wondering if I replaced the right sensor. The code is P0136, and it says Bank 1 Sensor 2. I was told by my mechanic that it was the downstream sensor, after the cat. There's only one sensor after the cat and that's the one I replaced. But can anyone confirm exactly where Bank 1 Sensor 2 is on an '02 4runner? Or provide a link to a diagram, I have searched for that as well and come up empty.

Now correct me if I'm wrong but if this was a short in the electrical wiring somewhere it wouldn't take 40 miles for it to pop back up right?

This is really going to get aggravating if it's something tough to nail down. I don't have the money to let my mechanic go on a fishing expedition, and this has to be fixed before I can get it inspected. Sigh.

[/UPDATE]

I just bought the truck last week. Was supposedly in great condition and recently serviced. Haha, yeah, well the first thing I noticed is the belts were shot. The alternator belt especially, it was actually shredded into strips. I was going to replace them myself, but it's been about 10 degrees the last few days and I don't have a garage, so I took it to my mechanic for that.

Then the check engine light comes on, as well as the VSC and TRAC lights, which I assume are simply disabled on general principles when the CEL is on. I know that traction control at least works (worked) because I had it on snow and ice before the lights came on and it was operational. Anyway, the code is P0136 which Autozone tells me is the downstream 02 sensor. When my mechanic was changing the belts I had him check that out and he confirmed that it did appear to be the sensor itself. It appears that's easy to replace, just wanted to find out if there's any preferred brand (or brands to stay away from) before I order one.

Also, how many sensors does this thing have? I'm tempted to just replace them all if it isn't too expensive. Kinda tight right now, I didn't plan on buying a new car. Some idiot ran me off the road and wrecked my old DD, which was a POS so I only had liability insurance on it. The idiot of course drove off so I got screwed on that deal.

Finally, when I tried the 4WD it didn't want to engage. The lights just blinked at me. I did this on dry pavement though, and this was after the CEL was on. I thought maybe the VSC and TRAC being disabled might prevent it from operating in 4WD or something, but when my mechanic had it up on his lift they engaged 4WD and had all four wheels spinning. He thought it might be moisture in the electric motors that engage the system, it was below freezing outside. At least I know the system works mechanically, probably just an issue with getting it engaged. Do you need to be on a slippery surface for it to engage or should it work fine even on dry pavement? This was in H mode and I just pushed the 4WD button, wasn't trying to lock the differential or anything.

I'm sure I'll have more dumb questions along the way, thanks for any help you guys can give.

Wally

 

OEM/ DENSO for the sensor. If you were stopped and not rolling a little bit, the gears may not have been lined up for it to engage.

 

No you don`t want to replace all the sensors it would be quite expensive!!!

Stick with Denso or Toyota Sensors these engines seem to like them better.

Just remember when you get a code it is the whole circuit not just a bad sensor the wiring and the ECM as well.

 

I was moving when I tried to engage it. The lights just blinked at me for a few minutes while I drove down the road. I gave up and turned it off, lights continued to blink for a bit before they finally went out. Then up on the lift at the garage it engaged and spun all four wheels just fine.

Yeah, I know, that's why I had my mechanic test the sensor itself. Said it wasn't doing anything.

Thanks guys!

 

Ok, ordered the sensor. Hopefully that will solve the engine light.

Tried the 4WD again today in a parking lot. Hit the button when it was in park and the lights just blinked at me. So I put in drive and slowly rolled it forward, after a few seconds it engaged and I got solid lights on the dash. So seems like it works, that's a relief.

 

bumpity