O2 Sensor (sub) Resitance Reading?

[Alexi]

Hi all. I decided to finally tackle my O2 sensor issue and have a couple of questions.

1) I tested the heater resistance of the main sensors (front) with a ohmmeter and the resistance was about 1.3 ohms on both sensors. Is that normal? The car had cooled down for about 2 hours so i'm not sure what the temp was. But is that reading ok?

2) I tested the resistance on the sub sensors(rear) and got no reading on both! Does that mean they're pooped or am i testing them wrong? There was only 2 wires on the sub sensors so i dont think i could've gone wrong??

Any help would be appreciated!

Thanks.

Al.

[Alexi]

Thanks for all your helpful input guys! Very helpful

Al.

[qha_vn]

2- all 4 ls400 OEM oxygen sensor has 4 wire, 2 for oxygen sensor, 2 for heater, if you find your sub with only 2 wires, i assume that they have been replaced with non OEM, so no reading is obvious

1- there is a way to test the oxygen sensor "in action", but i cant find the manual for you now, sorry

[Alexi]

2- all 4 ls400 OEM oxygen sensor has 4 wire, 2 for oxygen sensor, 2 for heater, if you find your sub with only 2 wires, i assume that they have been replaced with non OEM, so no reading is obvious

1- there is a way to test the oxygen sensor "in action", but i cant find the manual for you now, sorry

Thanks for your reply but yeah, the sub(rear) O2 sensors do have 2 wires only!

Look here.....

http://www.lexls.com/tutorials/EFI/suboxygensensor.html

Al.

[Robert Young]

I've just been working with Ox sensors on our Volvo, so these comments apply to Bosch sensors in a Bosch engine management system. However, some of my observations may be useful. The 4 wire sensors contain a heater (two of the wires, generally the same color because it doesn't matter how they are connected) and I believe a couple of ohms is probably about right, the Bosch sensor was 2.7 ohms cold. I purchased a PC based OBD code / sensor reader from http://www.autoenginuity.com/products.html and have been very happy with it, but check their site for any specific comments on Lexus compatibility. Note, the company also "sells" on eBay at a discount and if purchasing get the USB version for ease of use with a laptop.

With the OBD code / sensor reader, it actually collects and will plot a time history of the Ox sensor(s) and the impact they have on mixture control. I found that the second sensor on our Volvo had an output of zero volts (in-line engine with a single exhaust, 4 wire Ox sensors located pre and pst catalytic converter). I thought that this meant that the sensor had simply died and I replaced it, but the new sensor still showed zero volts at the OBD interface. I then started running harnes and found that the Ox sensor itself is probably operated using a current source from the engine control computer, with the difference in voltage between the two sensor lines the actual control signal. This is likely the reason that there is no apparent resistance on the sensor wires, the Bosch sensor didn't show any either.

In my case, the replace sensor showed good readings at the connectors, with a difference voltage of roughly 0.8 V (within the expected range). This meant that in my case the sensor interface with the engine control computer was working, as was the sensor itself (my orginal sensor was probably OK as well). What I think happened is that a differential amplifier inside the engine control computer has "crapped out" (background, I'm an electrical engineer by schooling from many years ago). I certainly hope your story doesn't end like this, because a new engine control computer from Volvo is $1250 and I'm looking for a used one. Fortunately, the car still runs fine but it might fail its next SMOG test in two years.

[LScott400]

Main O2's should be 5.1 - 6.3 ohms at 68 degrees F.

Sub O2's should be good if you don't have a Code 27 or 29.

If you want to perform the factory test on the mains:

EG406mainheatedo2.pdf

[AHJGTA]

The live test needs an oscilloscope. The front o2 sensor has sharp angled waveforms and the rear o2 sensor has delayed reactions with softer rounded waveforms.