No voltage coming from Lamba Sensor?? - PeachParts Mercedes-Benz Forum

ps2cho · #1 06-29-2008, 06:19 PM

I am trying to read the voltage from my Lamba sensor so I can see if the car is running too rich/lean as my misfire is *almost* gone now.

I have the positive pin of my multimeter in the Lamba sensor wire (the black one that plugs into the green wire in the passenger floor)....and the ground attached the chasis (tried different ground positions too)....

...but I'm getting no voltage read at all.

Am I missing something here???

I have the multimeter set to read volts....I tried both AC and DC modes...It was a pretty expensive Craftsman one so it can't be the multimeter....its only a month old.

Any ideas?

stevebfl · #2 06-29-2008, 06:40 PM

Verify your meter by measuring battery voltage.

It seems that you said you had closed loop duty cycle readings in one of your posts. That is all that matters about an oxygen sensor. The switch time gives a good idea about age and sensitivity and the duty cycle tells you the mixture.

If you want a specified low voltage standard to go on. Unplug the sensor and read the wire coming from the control unit, it should be .45v

ps2cho · #3 06-29-2008, 07:58 PM

Since I had the misfire fixed (He replaced a hose on the idle control valve and adjusted the transmission)....It runs alot smoother (not fixed though) but it TOTALLY killed my power. I'm gonna call him up tomorrow and ask if he did anything else because I don't understand how a hose or a transmission adjustment can affect my power....if anything I should have gained power. The car is just sooo sluggish.

Here's a weird one though -- all the readings are coming up backwards. Ignition on now reads 20% instead of 80% like it used to show (california) and the idle mixture reads 30% when it was 70% before. Does that make any sense??

Thats the reason I wanted to have the O2 sensor tell me if I was running lean or rich as I understand it gives 0.1v for lean and 0.9v for rich....so it should sit at or around 0.4v.

stevebfl · #4 06-29-2008, 08:19 PM

Duty cycle is a matter of point of view. 80% on equals 20% off.

Key on engine off should be 70% federal and 85% Ca. There is no duty cycle for ignition. It is for KE.

O2 sensors don't do good statically. It is about impossible to read .4v. The difference between .25v and .75v is almost insignificant in fuel quantity. Get a curve of stoiciometry and see.

TimFreeh · #5 06-29-2008, 08:27 PM

Quote:

Originally Posted by ps2cho

Thats the reason I wanted to have the O2 sensor tell me if I was running lean or rich as I understand it gives 0.1v for lean and 0.9v for rich....so it should sit at or around 0.4v.

When operating in "closed-loop" mode the sensor is not going to "sit" at any one voltage for more than a few milliseconds, remember that the sensor is feeding info back to the ECU to adjust the mixture. As the ECU changes the mixture the voltage on the O2 sensor will swing from lean->rich and then back to lean. At idle this pattern repeats itself 2-4 times a second if you have a healthy sensor, maybe once a second or less with a "lazy" or sensor.

If you use a multimeter to watch the O2 sensor voltage you should see it oscillating from .1 to .9 volts in a seemingly random pattern. A scope gives a much more meaning full view of O2 sensor operation.

ps2cho · #6 06-29-2008, 10:06 PM

Quote:

Originally Posted by TimFreeh

When operating in "closed-loop" mode the sensor is not going to "sit" at any one voltage for more than a few milliseconds, remember that the sensor is feeding info back to the ECU to adjust the mixture. As the ECU changes the mixture the voltage on the O2 sensor will swing from lean->rich and then back to lean. At idle this pattern repeats itself 2-4 times a second if you have a healthy sensor, maybe once a second or less with a "lazy" or sensor.

If you use a multimeter to watch the O2 sensor voltage you should see it oscillating from .1 to .9 volts in a seemingly random pattern. A scope gives a much more meaning full view of O2 sensor operation.

Yes I understand. The sensor reads 0v all the time. There is no voltage coming at all...thats the problem! I don't know what I'm doing wrong.

stevebfl · #7 06-29-2008, 10:11 PM

Hold your rpms up, the sensor won't read if cold. Does the line to the controller have the proper .45v when it isn't attached to the sensor?

ps2cho · #8 06-30-2008, 01:30 AM

Quote:

Originally Posted by stevebfl

Hold your rpms up, the sensor won't read if cold. Does the line to the controller have the proper .45v when it isn't attached to the sensor?

It was when the car was idling and at normal operating temperature....

I'll check the voltage to the controller tomorrow and report back.

Thanks guys.

stevebfl · #9 06-30-2008, 08:07 AM

It is the temp of the sensor I'm concerned with not the engine.

If the sensor heater is poor the sensor will not be hot enough at idle to generate. Does your duty cycle oscillate?

ps2cho · #10 06-30-2008, 09:25 PM

Quote:

Originally Posted by stevebfl

It is the temp of the sensor I'm concerned with not the engine.

If the sensor heater is poor the sensor will not be hot enough at idle to generate. Does your duty cycle oscillate?

Yes it does about + - 8%

Victor300E · #11 07-03-2008, 12:13 AM

ps2cho:

I too have no voltage coming out O2 sensor. It acts funny, when the car at certain temperature O2 sensor reads. When at some point voltage drops to 0 volts. I will buy new sensor and report back. And in terms of 8% duty cycle, I borrowed my mechanic friends $600 multimeter and duty cycle reads around 45% and my multimeter hovers around 8%. Try to use another multimeter and read your duty cycle again.

Let me know if you change your O2 sensor and your readings.

Thanks and good luck