Oxygen senor question about voltage reading (not fluctuating)

[alex 1993 525i auto]

Hi all,

I had my oxygen sensor replaced 6 months ago after codes 1221 and 1222 showed up. I tested the sensor with my digital multimeter (DMM) and I was reading 0.30V from pins 1-2 with the engine hot and running and the sensor connected. The thing is that the voltage was not fluctuating like it was supposed to do as in the Bentley manual. The sensor was 60K miles old so I wanted to replace it anyways. I bought a Bosch (part no. 11-78-1-468-620) from Pelican Parts.

That fixed the issue for 6 months and now the problem is back. Same codes are showing up. If I clear them they come back right away when I start the car. I am doubtful that the sensor was good only for 6 months so I checked with my DMM. It again shows a non-fluctuating, 0.22V which very slowly increase to 0.27V in 5 min or so. Voltage is present at the connector pin 3-4 when the engine is running (13.3V) which means the heater relay is fine. There is continuity in pins 3-4 on the sensor side, with about 5 mOhms of resistance.

What I understand is that if the O2 sensor readings are out of the map, the readings will go to a default by computer to a non-fluctuating voltage, and 1221-1222 codes will show up.

http://www.opel-scanner.com/files/DME_1.1_1.3.pdf

(I now I have a Motronic DME version 3.3.1 but I couldn’t find better info).

I checked for vacuum leaks as it is often the case for O2 sensor codes but I couldn’t find any, I have 24’’ of Hg vacuum when I check from the brake booster connector. Intake manifold gaskets and MAF are less than 1 year old.

So I’m heading towards buying a new O2 sensor... this time I’ll get a BMW instead of a Bosch OE...
Is my diagnosis process good or I should check something else?

Thanks!
Alex

[shogun]

I assume it is not the problem of the manufacturer, you have to find out why they fail. Bosch is a good product (although I like the Denso or NGK sensors more) and BMW also does not make them on their own, it is probably Bosch and just the BMW logo is added.
What was the color of the sensors? Here are some pics http://www.walkerproducts.com/oxygen-sensor-faq/
" pulled my oxygen sensor and it is an orange/black/white color. What does this mean?"
Lead poisioning
antifreeze contamination
rich fuel mixture
silicone poisioning
Visual inspection will show signs of lead poisoning, antifreeze poisoning, silicone poisoning, and excessive oil consumption. When performing a vehicle tune up, remove the oxygen sensor and check for these common oxygen sensor conditions.

http://www.aa1car.com/library/o2sensor.htm
http://www.lambdapower.co.uk/diagnosis/diagnostic_index.asp

[Rustam]

You should check for the mixture blance. If the mixture is lean, the voltage does not fluctuate, but holds at atound .3 or lower. If the mixture is rich, the volrage hokds steadily at about .7 or higher.

Please ask Shogun to share my saved website address(I dont have a record of it its been too long). There is a procedure for AFM but other than this the steps are same. You should look for whatever gives ability to adjust mixture in your car and refer to the mentioned procedure.

[Rustam]

Shogun, you have the web saved version of my site with AFM procedure that explains the reasons and theory, which are still same for MAF case. The problem is addressed there.

[Rustam]

Hi all,

I had my oxygen sensor replaced 6 months ago after codes 1221 and 1222 showed up. I tested the sensor with my digital multimeter (DMM) and I was reading 0.30V from pins 1-2 with the engine hot and running and the sensor connected. The thing is that the voltage was not fluctuating like it was supposed to do as in the Bentley manual. The sensor was 60K miles old so I wanted to replace it anyways. I bought a Bosch (part no. 11-78-1-468-620) from Pelican Parts.

That fixed the issue for 6 months and now the problem is back. Same codes are showing up. If I clear them they come back right away when I start the car. I am doubtful that the sensor was good only for 6 months so I checked with my DMM. It again shows a non-fluctuating, 0.22V which very slowly increase to 0.27V in 5 min or so. Voltage is present at the connector pin 3-4 when the engine is running (13.3V) which means the heater relay is fine. There is continuity in pins 3-4 on the sensor side, with about 5 mOhms of resistance.

What I understand is that if the O2 sensor readings are out of the map, the readings will go to a default by computer to a non-fluctuating voltage, and 1221-1222 codes will show up.

http://www.opel-scanner.com/files/DME_1.1_1.3.pdf

(I now I have a Motronic DME version 3.3.1 but I couldn’t find better info).

I checked for vacuum leaks as it is often the case for O2 sensor codes but I couldn’t find any, I have 24’’ of Hg vacuum when I check from the brake booster connector. Intake manifold gaskets and MAF are less than 1 year old.

So I’m heading towards buying a new O2 sensor... this time I’ll get a BMW instead of a Bosch OE...
Is my diagnosis process good or I should check something else?

Thanks!
Alex

Here is the saved copy of my site from webarchive. Goto AFM Adjustment at left side:
http://web.archive.org/web/20070403075208/http://mysite.verizon.net/vzerdcib/e34a/id4.html

[shogun]

Yes, I saved it for you here http://twrite.org/shogunnew/otherModels/E34/AFM%20adjustment.html

[alex 1993 525i auto]

Thanks for the link to the AFM adjustment but I mine is not adjustable I think, when I opened it last year it was just a small electronic card inside, no springs to adjust (part no. 13621747155).

As to the O2 sensor, I will try the trick to squeeze the fuel return line to make it run rich (or lean?) and to see if voltage jumps towards 0.8V (more V = more O2 reacting with the sensor?)... But the readings on the DMM were very steady close to 0.25-0.30V, they were not jumping at all between 0.2-0.8V like it should. https://www.youtube.com/watch?v=SLgdaWCuKVo
(close to when you test the AFM too)

Anyways like Shogun suggested I'd have the sensor removed , cleaned and tested out of the car if possible. Too bad I didn't keep my old one to compare...

[Last time I had the sensor replaced in a repair shop... I tried to do it myself but I can only put my car on ramps. There was not enough space under the car to remove the O2 sensor, I couldn't have enough torque on the sensor with the foot of space under there (it's between the cat. and the firewall). I guess I would need to lower the exhaust to get better access to the sensor? Even on the lift, the guys said it was not easy to remove...]

Thanks guys, let me know if you have other ideas/infos!
Alex

[shogun]

It might be that the wires are somewhere broken from sensor to Motronic. I usually check the O2 sensor on the motronic directly with engine running, engine must be at operating temperature. Do not know the pins on that Motronic, do you have to check on the online ETK the pins.
This is how it works http://www.bimmerboard.com/forums/posts/622383/
or the O2 sensor relay?
I also made myself a tester where we can easily see the bulbs fluctuating. exhaust, gas, oxygen monitor
Actually it is for this, bought it from Australia as a diy kit http://www.bimmerboard.com/forums/posts/606428/
http://imageshack.com/f/4noxysensortesterbs3p
Here we are testing it on an Alpina B12 E32, https://www.youtube.com/watch?v=K8miz_1aHYw

[Rustam]

Thanks for the link to the AFM adjustment but I mine is not adjustable I think, when I opened it last year it was just a small electronic card inside, no springs to adjust (part no. 13621747155).


?

I never implied nor stated that MAF would have a spring like AFM does. The idea that MAF has an electronic card inside is a well known fact. In fact I did say that MAF is different.

The implication was an adjustment screw, which some MAFs do have. The challenge was to look and see if yours is such, and follow the adjustment procedure.

[Rustam]

Yes, I saved it for you here http://twrite.org/shogunnew/otherModels/E34/AFM%20adjustment.html

Thank you, Shogun, for your diligence.

[alex 1993 525i auto]

Hi,

I had the O2 sensor replaced, this time with a BMW sensor, part 11781735710 (bought it from ECS Tuning). All is good now! The car runs great, no more CEL, since 2 days! The worn sensor is on its way back, I got a return authorization.

Out of curiosity I tested the voltage of the new working O2 sensor installed. It gives me a steady voltage of 0.43V, it is not fluctuating at all, my old sensor was not fluctuating as well but wat reading 0.30V… Oh well. Also, the old sensor was a bit black carbon covered. Like if it was running rich (but at 0.30V it should be lean?) or if the engine was burning oil (but oil level doesn't move at all).

Relooking at the links Shogun sent : http://www.aa1car.com/library/o2sensor.htm

I found this : [On some newer vehicles, a new type of Wide Ratio Air Fuel (WRAF) Sensor is used. Instead of producing a high or low voltage signal, the signal changes in direct proportion to the amount of oxygen in the exhaust. This provides a more precise measurement for better fuel control. These sensors are also called wideband oxygen sensors because they can read very lean air/fuel mixtures.
The OBD II system monitors converter efficiency by comparing the upstream and downstream oxygen sensor signals. If the converter is doing its job and is reducing the pollutants in the exhaust, the downstream oxygen sensor should show little activity (few lean-to-rich transitions, which are also called "crosscounts"). The sensor's voltage reading should also be fairly steady (not changing up or down), and average 0.45 volts or higher.]

My car has OBD 1 system but the other than that this explanation fits with what I observe when reading O2 sensor voltage.

If anyone has better clues about the sensor voltage not fluctuating let me know. For now I'll assume the testing procedure in Bentley is not accurate...

Thanks for your help!
Alex

[shogun]

This sensor is only used by 525 E34 M50 engine, it has 4 wires, no idea why yours works like that, but maybe it is a special one for this engine. http://www.etk.cc/bmw/EN/parts/fullAppliance/11781735710
google search tells me: bmw 11781735710 - Alternative oxygen sensors
Replacement oxygen sensors for bmw 11781735710:
Airtex 5S3108,BMW 11781735710, Bosch 13108, Denso DOX-1369, NTK (NGK) 25042, Walker 250-24021,

Searching with the BMW part number I found an old thread from 2007 and there it mentions that this car has a Siemens engine control module/DME http://www.bimmernut.com/forum/showthread.php/33656-O2-Sensor-for-Siemens-DME
http://www.bmwswap.com/index.php/en/bmw-information
http://www.meat-doria.com/en/product_meat/81080


In a German forum I read that this o2 sensor is only / especially for DME Siemens MS40 and the material is titanium oxide, cable wires are also different: Titandioxid. Kabel - rot, gelb, schwarz und weiß.

[alex 1993 525i auto]

Ok thanks Shogun!