O2 sensor testing (1 Viewer)

[WCBlueSky]

As part of baselining, I wanted to check if the O2 sensors for my '94 LC were operating correctly. I happen to own an oscilloscope, so I hooked it up to the diagnostic port. The bank 2 sensor responds very quickly and has the correct average of around .45 volts, while the bank 1 sensor is really sluggish and has an average value lower than 0.45 volts, especially at idle, which is biased lean. The bank 1 sensor also has a lower amplitude--it doesn't span the full voltage range in constant operation. No check engine light. I ordered a new sensor for bank 1, hopefully it will fix the offset lean issue. Otherwise I may have to go digging: check the fuel injectors, etc...

 

[ppc]

I would replace both sensors at the same time even though one may not be functioning as weakly then you know both should be functioning the same. That is why Toyota sold them in pairs for the 93-94 models.

 

[bigredmachine]

you can have a bad o2 sensor with no check engine light on an obd 1 truck. repalce them as a set, denso are preferred but i have had no problems running the ntk at about 1/3 the cost.

 

[fjbj40]

NTK is OEM for 93-94, Amazon is best deal.

 

[Desert Dino]

NTK is OEM for 93-94, Amazon is best deal.

Naaa Rockauto

 

[SnowroxKT]

I bought 2 of the 24044 ones off rockauto for a good price to try and solve a Code 28. Unfortunately I still have a code 28... I metered out both sensors with my Fluke 87V and they didnt pass the 5.0-6.5 Ohm test at 4.8 and 4.9 Ohms. So those are getting sent back, one is getting replaced.

@WCBlueSky where did you hook up the scope? I may need to do that.

I have a strange feeling I may need to repair the wiring from the main harness to the sensor plug. I've currently relocated the sensors to the PAIR location and they do stay much cleaner there.

Maybe I can meter out the harness from the sensor plug to the diagnostic port... hmm. I did verify that I was getting 14V at the sensor when the engine is running.

 

[Rifleman]

WCBlueSky, Below you'll find 2 links that i think you may find helpful. On the first link, start at page 30-1, that's where the O2 sensor information starts. Next is a link to another web page that has some helpful trouble shooting information.

https://www.autonerdz.com/yabbfiles/Attachments/TCCS__TOYOTA_COMPUTER_CONTROLLED_SYSTEM_.pdf

Vf1 voltage

Vf voltage information about Oxygen Sensor

alflash.com.ua

 

[fjbj40]

I bought 2 of the 24044 ones off rockauto for a good price to try and solve a Code 28. Unfortunately I still have a code 28... I metered out both sensors with my Fluke 87V and they didnt pass the 5.0-6.5 Ohm test at 4.8 and 4.9 Ohms. So those are getting sent back, one is getting replaced.

@WCBlueSky where did you hook up the scope? I may need to do that.

I have a strange feeling I may need to repair the wiring from the main harness to the sensor plug. I've currently relocated the sensors to the PAIR location and they do stay much cleaner there.

Maybe I can meter out the harness from the sensor plug to the diagnostic port... hmm. I did verify that I was getting 14V at the sensor when the engine is running.

One of the O2 harness comes over the transmission right at the rear of the engine. I had a problem there. So I tied a string onto it and pulled it back to the drivers side to ease the repair then pulled back over with the string.

 

[SnowroxKT]

One of the O2 harness comes over the transmission right at the rear of the engine. I had a problem there. So I tied a string onto it and pulled it back to the drivers side to ease the repair then pulled back over with the string.

Interesting, I thought it was on the passenger side where it connects. I'll have to look over it carefully and go from there. Thanks for the tip.

 

[fjbj40]

Interesting, I thought it was on the passenger side where it connects. I'll have to look over it carefully and go from there. Thanks for the tip.

It does connect on passengers side but it comes out of the main harness on the drivers side (our of the loom), If it’s at the plug then it’s easy, but mine was damaged over the tranny so it had to be pulled over.

 

[SnowroxKT]

It does connect on passengers side but it comes out of the main harness on the drivers side (our of the loom), If it’s at the plug then it’s easy, but mine was damaged over the tranny so it had to be pulled over.

Wtf is this and does anyone have a pinout?

 

[SnowroxKT]

So more my question is regarding the shielding blue colored wire. This has obviously been cut and repaired very poorly previously.

 

[fjbj40]

terrible repair!
Shielding or lack of proper shielding will cause interference for the signal.
Those need to be environmental or heat shrink splices.

 

[WCBlueSky]

Replaced the bad O2 sensor, the waveform is waaaaay better now. The exhaust seems less nasty too.

 

[338Lapua]

Are the o2 sensors know to be bad when bought new? Ive got 2 Denso sensors that when reading with a multi meter only read in MV. The good one I have reads in volts and stays around .45 which is within spec. Ive been trying to chase down a lean CEL on a 93.