yup.I even squirted pb blaster on it to let it soak overnight.I'll try again tonight.Shouldn't the O2 sensor throw a c.e.l. when it's disconnected?
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3-wire O2 sensor wiring....
- Thread starter daves66nova
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It will, but it may take two drive cycles (or more) for the CEL to come on. If you had a scantool, you would see a pending code first, then the CEL would come on one or more drive cycles after that.
daves66nova
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drove it home from work yesterday,drove it work this morning,nothing so far.
So again why were you attempting to change the original downstream 02 sensors in the first place? It would've saved you a lot of time to just get the proper 2-wire O2 sensor anyway. It goes back to what Brianl said earlier that you might need a torch, only this time for getting the old O2 sensor out without breaking anything off in the exhaust.
daves66nova
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I was able to change it out already. I wanted to change it out since it had 180,xxx miles on it. I'm pretty sure it was past its life.Yesterday i disconnected the pre-cat sensor and the check engine light still didn't come on. Is there a fuse for this light? How can i check for codes?
You need an OBD-II code reader, or find someone who has one and will let you borrow it.
There's no fuse for the check engine light that won't either power down the instrument cluster or the whole ECM if removed.
There's no fuse for the check engine light that won't either power down the instrument cluster or the whole ECM if removed.
daves66nova
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The car's a 95 OBD-I.I've checked and there's no port to plug in an oBD-II connector.
That's pretty odd, it has a post-cat sensor but it's not OBD-II.
Why did you think you needed to replace the post-cat sensor anyway?
Why did you think you needed to replace the post-cat sensor anyway?
daves66nova
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I think it's the original one still.It says toyota on it.I've disconnected both of them and i still don't get a c.e.l. Why is that?
daves66nova
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I've checked under the hood and it does say obd-I
On a Toyota/Denso sensor the blue wire is signal, and the white wire (if present) is an isolated ground. The pair of black wires on a four wire sensor are for the heater.
Bosch and Bosch-licensed sensors use a pair of white wires for the heater power, and the black wire is for the sensor output. A gray wire, if present, is for the isolated ground.
All oxygen sensor use the same zirconia sensor element, and output the same signal. The difference is solely how they are wired.
The "isolated ground" is a separate reference wire for the sensor. Just like with an audio signal, it avoids electrical noise that might confuse the computer. An exhaust system often doesn't provide a good ground because of insulting gaskets and rusty fasteners. And with certain materials there is a voltage generated with a temperature difference.
If your system was designed with an isolated sensor ground, you should really replace it with a sensor that has a isolated ground. It will *probably* work just grounding that "extra" wire, but you can't be certain that it is working properly or optimally.
You can test a sensor with propane torch, but it will only generate a signal with the flame applied. As soon as the flame is removed the output voltage will drop to zero. The test is to get the sensor hot (it won't respond while cold) and then rapidly move the flame cone over the sensor. As the different sections of the flame cone move over the sensor, the lowest oxygen concentrations will generate the highest voltage. A good sensor will respond quickly, while a degraded sensor will take a second or two to change output.
Bosch and Bosch-licensed sensors use a pair of white wires for the heater power, and the black wire is for the sensor output. A gray wire, if present, is for the isolated ground.
All oxygen sensor use the same zirconia sensor element, and output the same signal. The difference is solely how they are wired.
The "isolated ground" is a separate reference wire for the sensor. Just like with an audio signal, it avoids electrical noise that might confuse the computer. An exhaust system often doesn't provide a good ground because of insulting gaskets and rusty fasteners. And with certain materials there is a voltage generated with a temperature difference.
If your system was designed with an isolated sensor ground, you should really replace it with a sensor that has a isolated ground. It will *probably* work just grounding that "extra" wire, but you can't be certain that it is working properly or optimally.
You can test a sensor with propane torch, but it will only generate a signal with the flame applied. As soon as the flame is removed the output voltage will drop to zero. The test is to get the sensor hot (it won't respond while cold) and then rapidly move the flame cone over the sensor. As the different sections of the flame cone move over the sensor, the lowest oxygen concentrations will generate the highest voltage. A good sensor will respond quickly, while a degraded sensor will take a second or two to change output.
daves66nova
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Well, nothing yet. It's been about 5 days now with both sensors disconnected and no check engine light on yet.
daves66nova
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It finally came on! I was going down the freeway when it finally happened.I connected the pre-cat sensor and the light went out.
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