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  #1  
Old 04-12-2019, 11:03 AM
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Testing O2 Sensors & MAF Sensor with a multimeter

Hi Everyone,
2004 X5, 3.0i, E53. 160k miles! Still running great!
I'm going to test these sensors with a multimeter before getting new ones.
I know how to set up the multimeter for them. I need the volt value for the MAF and Ohms for the Oxygens sensor.
For the MAF, I got around 0.8v at idle and 1.8v at high revs. Are these within the range? And also what Ohm values should I expect for the O2s?
Thanks
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Old 04-12-2019, 12:08 PM
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You won't be able to test for life span with a meter. You can read real-time values but the exact number that is good or right for your exact car will not be the same for everybody else. The DME figures it out.

When the calibration that your DME figures out for your car ends up with a lean or rich always situation, it can likely be a worn out MAF.

It's just about the most difficult thing to determine on a car, usually done by replacing everything else first.

I was about to replace my MAF because out of the blue i started getting continuous lean errors, most often from vacuum leak or rarely the MAF. It can also be from injectors plugged or a weak fuel pump. Well fuel pump died on me the past Wednesday so mystery solved in my case.

Using a decent scan tool and watching fuel trim values will get you better Intel for figuring out MAF life
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Old 04-12-2019, 12:53 PM
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I was curious to know as well for the MAF as someone pointed out that it could be the culprit for my random misfires.

Always thought a faulty maf would throw a specific P code but guess not if it’s “worn”

But seeing live data with inpa it was within range but obviously not when it threw the misfire codes.
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Old 04-12-2019, 01:05 PM
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Please guys have a look at these clips and see what you think

For MAF test
https://www.youtube.com/watch?v=O4pBu3uRlYA
For O2 Sensor test
https://www.youtube.com/watch?v=7uqmYkl7t0c&t=338s
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Old 04-12-2019, 02:19 PM
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Are you maybe hunting for a problem that doesn't exist? Is there anything wrong at all with those sensors other than the 160k mileage?

BTW, shortly after getting my 2001 3.0i at around 168k miles a few years ago, I replaced the O2 sensors with no problems at all, just dreaming for better MPG. No change except a slight lightening of my wallet. Same with spark plugs, BTW - I think they were the originals I pulled out of there. Still looking and working great at 169k miles.
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Old 04-12-2019, 02:44 PM
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the MAF test above just shows that it's working, not that it's working properly.

Same for the O2 sensor; just basic 'does the part exist' tests shown.

Are you trying to root out a problem you suspect is related to the parts?

I swapped mine and wife's MAF a while back to see if problems I was having would migrate to her = nope. Problem stayed on my car. I was having consistent lean code related problems on the post cat O2 sensors, and two days ago my fuel pump hard failed, so i suspect it was weak for a while and finally died i never got a chance to measure the pressure.
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Old 04-12-2019, 04:41 PM
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For the 02, the Ω reading (presuming you mean for the heater) will also be very hard to get an accurate reading because they are very low resistance on the order of an ohm.

I've found that if I'm getting heater errors I've been able to reset the DME O2 calibration by unplugging the O2 for two engine starts and plug them back in.

At the age of your car if the parts are original it's overdue for replacing all.

Use OE or OEM only for MAF or for O2 (at least for pre cat sensors)


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Old 04-13-2019, 10:07 AM
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[QUOTE=andrewwynn;1159832]the MAF test above just shows that it's working, not that it's working properly.

Same for the O2 sensor; just basic 'does the part exist' tests shown.

If you watch the first video towards the end, it does show that voltage increases as the engine is revved up. The shows MAF is good. If it doesn't, it means that it definitely is bad.
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Old 04-13-2019, 05:03 PM
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Voltage changes just means it's not completely broken. Working but working badly is the main problem with worn out MAF. It reports slightly wrong value.
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