O2 Sensor Faulty - '90 240

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Old Oct 22, 2020 | 01:25 PM
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Reun's Avatar
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Question O2 Sensor Faulty - '90 240

The check engine light is on. Ran the diagnostic and got 2 faulty codes. 2-1-2 Faulty O2 sensor or wiring and 3-3-4 TPS in idle.
2-1-2 O2 sensor. How do I know if it is faulty wiring or faulty sensor itself? I know I can replace the sensor fairly easy (with the right tools and muscle) but the part is $$$ and I don't want to waste my money if the wiring is the actual issue. 3-3-4 TPS in idle. Does this have something todo the the O2 sensor?? From what I've read its another wiring issue or incorrect adjustment. How would I go about the next set of diagnostics and testing to make sure I'm not wasting my money? Id really appreciate some advice thank you!
 
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Old Oct 22, 2020 | 03:04 PM
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hoonk's Avatar
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Originally Posted by Reun
2-1-2 Faulty O2 sensor or wiring and 3-3-4 TPS in idle.
How do I know if it is faulty wiring or faulty sensor itself? I

I don't want to waste my money and testing to make sure I'm not wasting my money?
Have you cleared the codes and driven it again to see how long it takes for them to come back?

You can test the O2 sensor with a volt/ohm meter. The fat green wire is the output - the 2 black wires go to the heater. 12v +and - are on the black wires, there should be very little resistance through the two black wires on the o2 sensor (there's just a resistance heater in the sensor) the fat green wire - you can measure voltage - connected and running the voltage should flash between ~.3-~.8 volts. You can artificially change the o2 output voltage easily to see if will respond to a rich or lean mixture. Disconnect the green wire and hook a voltmeter to the black o2 lead of the sensor (and ground) . With the engine running ground the green wire from the body to someplace close on the firewall - this will tell the ECU that it's lean and will richen the mixture - you should see the voltage increase to maybe 1 volt. Then lick a finger on each hand, hold the green wire between your fingers in one hand in one and touch the positive battery terminal with the other - this will send a small voltage (through your body) to the ECU telling it that it's rich and lean the mixture out. You should see the voltage decrease - maybe to 0.

And smart move to not just replace parts that you have not proven are bad. You can drive the car without the O2 - it's function is to make sure the Mixture is exact for the converter to operate most efficiently.
 
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