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Resolved No O2 Sensor Voltage and Unable to Find it!

Pasta_Ricer

Probationary Member
27
2
Nov 2, 2021
Zanjan, Asia
Hello again.

My weird Galant will never seize to amaze me that it can run and pull great while having half of the stock stuff replaced by crappy fake Peugeot parts or removed entirely.

Me being an electronics tinkerer, I got really interested in O2 sensor and I wanted to get a $12 one to mess around with. While doing some research about them, I got really curious and I thought I should see if I can tap into the one on my Galant. I found the pinouts on the ECU, connected my multimeter, and... nothing. :/
I fully warmed up the engine and still the same 0.0160V which is basically a voltage offset caused by the voltage drop on the chassis ground. It did not respond to my revs.
Naturally, I tried to look for the sensor and see if I could spot a problem like a broken wire or something, and again, nothing.

My car seems to have had its cat removed before it got to my hands since there is nothing that resembles a catalytic converter as far as I know.

Am I looking in the wrong direction or is it really missing?

Where does the harness for the sensor go so I can trace it and hopefully find it tucked into a corner or something?

Can I use a heated O2 sensor from a different car instead and hook up the heater wires to the MPI relay?

I have attached some videos of the underside of the car. Maybe you guys could take a look and point that I was wrong? :)

Thank you so much <3

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Solution
Hey!

I just figured out what's going on and spoiler alert, I don't have an O2 sensor!

Yes, my cat has been deleted.
Yes, the sensor could have been thrown away or something.
BUT, I still have a wire attached on the ECU for the sensor and the first clue would be that it's almost gray instead of white which should be for the O2 sensor.

I got really annoyed today when I couldn't find the sensor and tried to follow that gray wire. Did lots of multimeter continuity checks and I found where it goes!

20220924_205918-jpg.674169


Apparently, my car doesn't have an O2 sensor from factory and instead has a potentiometer to change the AFR by simulating an O2 sensor voltage. And yup, it's the same...

Pasta_Ricer

Probationary Member
27
2
Nov 2, 2021
Zanjan, Asia
And yes, I do have lots of soot in my exhaust system and on the pistons when I had taken out the spark plugs to clean.

I forgot to add the second video so I've uploaded it below this post.

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luv2rallye

DSM Wiseman
8,393
1,169
Jun 7, 2003
Minneapolis, Minnesota
Yes I can see the cat is missing (straight pipe welded in). Which O2 sensor are you trying to measure? Because without the cat that one is now missing and would then obviously read 0v on it's ECU pin. The O2 on the exhaust down pipe should still be there however.
 

Pasta_Ricer

Probationary Member
27
2
Nov 2, 2021
Zanjan, Asia
Hey!

I just figured out what's going on and spoiler alert, I don't have an O2 sensor!

Yes, my cat has been deleted.
Yes, the sensor could have been thrown away or something.
BUT, I still have a wire attached on the ECU for the sensor and the first clue would be that it's almost gray instead of white which should be for the O2 sensor.

I got really annoyed today when I couldn't find the sensor and tried to follow that gray wire. Did lots of multimeter continuity checks and I found where it goes!

20220924_205918-jpg.674169


Apparently, my car doesn't have an O2 sensor from factory and instead has a potentiometer to change the AFR by simulating an O2 sensor voltage. And yup, it's the same weird part that I posted in my other thread, looking for some info on the adjustment with "P" and "I" labels. As it turns out, I had a dummy moment and misread them as they are supposed to be R and L, standing for rich and lean. Then, everything just clicked.

By turning that, you can richen or lean out the mixture with ease. Pretty neat!

I wonder if I can remove that, put a hole in my exhaust, and just use a cheap O2 sensor to get consistent results and stuff. A heated sensor would be much better.

So yeah, the adjustment was set on full rich mode (emulating a lean 0V O2 sensor signal which would tell the ECU to make it rich) and I turned it up to be a bit leaner and yep, I don't get that super nasty exhaust smell that the whole family complained about every time I fired up my car LOL.
 
Last edited by a moderator:
Solution

1990TSIAWDTALON

Moderator
9,673
5,508
Nov 14, 2013
Independence, Kansas
Well isn't that a weird device.....allows the owner to change the richness or leanness. I've never seen one before. Thanks for the post!
 
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