'81 Corolla oxygen sensor & idiot light

[Limnos]

Just as my 1981 Corolla clicked over to 120,000, the "Sensor" warning light came on. First I'll say this is a pre-computer car so forget about hooking it up to a reader to check codes. The user manual says it does this automatically every 30k to get you to go in and have the oxygen sensor checked, whereupon the dealer will also reset the switch. So:

1) How do I reset the switch without resorting to the dealer? My Haynes manual says almost nothing about O2 sensors and nothing at all about the warning light.

2) The owner's manual says the dealer (who, by the way, no longer even has '81 parts in the computer database) will check the sensor for operation and then reset the switch. Is this "checking" something a home mechanic can do (and how)?

3) Maintenance replacement vs. check vs. do nothing? The car is otherwise running fine. MN no longer does emissions tests so I can't say what's happening there but I don't see any blue fog. What's the philosophy on O2 sensor replacement? Honestly, I still have some of the original belts in this car so my attitude re. Corollas is things last forever until you really have to replace something, then that part subsequently requires frequent replacement because the replacements are never as good as the originals. I don't think this sensor has ever been replaced. Should I do this? A replacement costs $30-$60 which is cheaper than a visit to the mechanic for "checking" (and assuming I can otherwise find out how to get the darned light to go out!), but is this a case of, "Don't fix it if it ain't broke"?

Thanks for any feedback, especially if you know how to get that light to go out (time-honored black electrical tape over the light is not a preferred solution!).

[racejockey]

Actually yes I have the same problem. My check engine light is on as well and seems to go away after 120km/h. The car is running fine, the previous owner had changed the engine and says it could be the o2 sensor. If you find out how to turn it off, could you tell me? thanks.

[Limnos]

After posting on this forum and alt.autos.toyota (the newsgroup was very helpful), I've got the light out. For the 1981 Corolla there is a small white box (about 1" x 0.75" x 0.5") at the end of blue, yellow, and red wires leading from the main wiring harness by the drivers left foot (US models). I think this normally hooks onto the top of the panel with the speaker grill on it (there's a metal clip on the side of the box), but in my car it had fallen behind this panel making it tough to find (I had to unbolt the panel to get it out). The box has a cap that flips open and reveals a slide switch. Moving this switch to the other setting that it is currently in resets the sensor light for another 30,000 miles.

Note that in this pre-electronic version of the Corolla this is not a "check engine" light. It is an oxgen sensor reminder light that is not connected to the emissions computer at all, but is only connected to the odometer. It is not reporting the actual sensor condition and resetting the light does not exclude having to test the sensor. I finally bought a copy of the 1981 Toyota Corolla service manual (the pricey one put out by Toyota) to find out how to properly test the sensor. There's one or two parts to the vacuum system that need to be temporarily disconnected, then it's a matter of using a tachometer to help run the engine to 2500 rpm and using a voltmeter to test for output from a special test connector up near the brake and manual transmission fluid reservoirs.

I don't know about Chilton's, but the Haynes manual fails on the oxygen sensor. They don't mention it at all in the index, and in reading the manual cover to cover the sparse mention doesn't include any information on how to test the sensor or reset the light (unless you're good at figuring out things from wiring diagrams). This is a disappointing omission since it is within the capability of a person who can do things like change their own sparkplugs, and is is something that is guaranteed to come up every 30,000 miles.[

[UNCLE BUCK]

Great post - thanx! - Sensor Light just went on in my 81 Shoebox S/Wagon - Auto

[Limnos]

You're welcome. It's nice to know it was worth doing a full write up! P.M. me if you need more information. I haven't read this forum in months but a PM should hopefully bounce to my email to notify me. I think it's a pretty small community out there now with '81 wagons so resources are handy.

Brian