Engine light, oxygen sensors, cat, 1988 2wd automatic

[Fillupamerica]

My engine light comes on after a few miles (8-10 miles) and will stay on until engine turned off. I jumped the eingine light wire and the blinks go in this order, 2, 5, 2, 6, 5, 1. When checked with "1988 and 1989 Toyota Vanwagon Diagnostic Codes" it says code 21. Oxygen sensor and/or oxygen sensor heater. My gas mileage dropped from 23-24 to 18-19, and perhaps there is less power, and definitely extra heat in the cabin (the lining on the engine cover is missing). Is this because the o2 sensor isn't working, so the computer uses the default setting running rich on gasoline causing excess heat and low gas mileage?

Questions:
1. Is there a way to test each unit to tell me which one is not working properly?
2. What is the cat, and where is it located?
3. Could it be something else that I am unaware of?
4. Could it be the o2 sensor circuit and/or o2 sensor heater ciruit? where is this located on the vehicle?
5. I was staying at a camping area with a lot of mice, perhaps was a wire eaten through or....?

Side note: My oil light comes on after 3 to 4 hours of driving, (only on long hauls does this happen) and will intermittently go on and then off and on and then off etc... Why is this? Perhaps because of the oil being warm, causing the mechanics to expand and be a little bit loose?

edit: I also smell gasoline coming out of the gas cap. Could be the gas cap doesn't fit as tight, I lost the original and bought this a year or so back, but it never smelt of gasoline before.

[llamavan]

In all likelihood, your front O2 sensor has gone south (speaking from experience). I would just replace it and not bother testing it unless there is a history of premature failure. O2 sensors ARE a wear part.

If you can find your battery box from underneath, you can find the cat, and also the front O2 sensor. It's a big oval can-looking thing bolted into the exhaust system (that runs down the left side of the van). The front O2 sensor is mounted in a port in the exhaust pipe after the exhaust manifold (or in the end of the exhaust manifold, in the case of pre-1988 vans). It's the only thing mounted in the exhaust piping with a wire going to it. There may be a shield over it, or the shield may have deteriorated by this time.

You can track the O2 wiring back to where it enters the wire harness if you are concerned about it being broken (this does happen), but if a rat got in there, this won't be your only problem (and you will likely see a lot of obvious damage besides wiring). Mice are usually not an issue unless you install some of the buggers directly in the van, and even then they tend to prefer other stuff (like insulation and old potato chips).

Gwen

[Fillupamerica]

all right! Good deal! Got the part, spliced all the wires, threw it back onto the pipe, and she sounds fine. Gonig to fire her up in a bit and take it for a spin. I know this has been posted elsewhere, I'm not finding it, how do you reset the engine light?

also, I ran the test for the engine light, and instead of blinking like before, it's now blinking 5-1. I think this is the AC unit I ripped out and left a wire hanging. To fix, could probably ground the correct wire, no?

hopefully she's back to full capacity. next things next, rotors!!! dun dun...

[llamavan]

how do you reset the engine light?

Remove the EFI fuse or disconnect the battery. I forget exactly how long Toyota says (I know it's different depending on temperature and which generation van) and I'm too lazy to look it up, but 15 minutes will overdo it nicely regardless.

Gwen