I've lurked here for a long time. I have a 1988 4x4 truck with about 200,000 miles. It leaks and is rusty but has been good to me since I bought it 15 years ago. It has been running rough lately so I changed plugs, wires and had a tune up at the local garage. I found from this forum that I can check for codes with a paper clip which I did and got a 21 and 51. I don't think the oxygen sensor has been replaced since birth and went to see what it would involve. It seems to me that I will need to take the carpet up out of the cab and take the seat out. Is that right or is there a trick? This forum has been great and I have learned alot. I just can't find a thread that seems to address my specific issue. I will be happy to put up pics if that will help. Thanks for all the great advice.

 

No shouldn't have to do anything in the cab. Provided the nuts aren't just mounds of rust at this point in their life, just unbolt the old sensor from exhaust pipe disconnect wiring connector. And reverse to install. Don't forget a new gasket.

 

Gotta ask, where did you get the impression you needed to remove interior parts?

 

Yeah that's a weird one...maybe you were thinking of the fuel pump? Oh wait, that's a first gen 4runner isn't it? But yeah, you unbolt (2 bolts) the O2 sensor from the exhaust manifold and can access from the engine bay. Don't forget to adjust timing and valves too if you can...and an air filter.

 

I'll take a picture so I can either show you how weird the design is or how dumb I am to try and work on my own vehicle. The sensor goes straight to a wire that goes up into a rubber sleeve type thing that goes into the cab. I lifted up the carpet just a bit and found where it comes into the cab. That ends up with a connector under the seat. Like I said I will go get a picture so I can make a fool of myself. Thanks for the quick responses.

 

I just had my seat out, and yes the plug goes under the seat. I am not sure if you would have to pull the seat, but it is not hard to do.

 

Thanks Stan. My ego will survive the day.
Thanks for the response guys.

 

88 manual shows it with a gromet and panel clip, interesting. Good news is yours can't short out to the transmission Bad news is depending how that body clip is oriented It might be best to attack it w/o the seat in the way. Lots of lube on the seat bolts from underneath, and take care not to cross thread them putting it back.

 

Is there any other reason for a 21 code besides oxygen sensor? I can't believe it gave out after only 200,000 miles... Thanks again for all the help.

 

test it already? Could just be a loose or dirty connection. they're actually pretty tough, you can clean the gunk off the ceramic and they're almost good as new, so long as the heater-driver doesn't malfunction and the ceramic case is intact the heating element won't fail.

 

200,000 miles? Man, they sure don't make car parts like they used to ....

21 is "Open or short in heater circuit of heated oxygen sensor". Circuit includes all the wiring. The heater itself can fail (obviously), so I would start by replacing the sensor. If that doesn't do the trick, you'll need to follow it up with a little multimeter work.

 

Learn something new everyday, just checked my 89 runner sure enough no connector but a grommet going into the cab. Touche

 

Thanks for taking the time to help me out. Like I said, lots of leaks and rust. My clutch has just started slipping and I'm going through hydraulic clutch juice pretty quick. It's starting to get warm in Montana so I will probably be back with lots of noob questions. Thanks again everyone for the help. Wealth of knowledge and patience here.

 

Can someone tell me if it's ok to take the o2 sensor off cause the person I bought the truck from cut the wires so can I leave it off or what and what does it do for the truck anyway and its a 82 pickup by the way and I live in Louisiana so I don't have to pass smog if that has anything to do with it

 

http://www.autoshop101.com/forms/h24.pdf
"site:autoshop101.com oxygen sensor"

 

well it is still in there to plug the hole in the exhaust pipe.

So if your doing a new exhaust since it is not working now just leave it out if your happy with the way the truck runs.

 

What on Earth... I have to fight tooth and nail with frozen seat bolts and remove the seat to plug in my new O2 sensor? For God's sake why would they do that? This could turn into a multi-day project if one of those bolts snaps. I'm hoping I'm misreading the above posts.