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NOx Sensor Testing?

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5 years 5 months ago - 5 years 5 months ago #23906 by graywave
NOx Sensor Testing? was created by graywave
I recently went to a Dodge / RAM ECO diesel class which was great for getting my foot in the door with these engines.

Im curious about NOx sensor testing and values to look for. From what i know, NOx sensors are basically oxygen sensors that are designed to break down the NOx and measure the O2 in the gas.

Now specifically on a 2015 RAM ECO Diesel, the NOx sensor i believe directly connected to a control module tuned for that sensor and according the a wiring diagram there is only a power, ground, CAN H and CAN L going to the module. Back probing the sensor for voltages is out unless you pierce the wiring between the module and sensor and all voltages you see in the scan tool is all processed data which may or may not output raw voltages during a fault or even output quick enough.

I assume they also have a heater element?

Anyone know more about these sensors and how they can be used to diagnose running conditions?

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Last edit: 5 years 5 months ago by graywave.

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5 years 5 months ago #23961 by Tyler
Replied by Tyler on topic NOx Sensor Testing?
You've got about as much info as I do. :unsure: I can go over my class manuals when I get home in case I missed anything.

But yeah, no direct sensor testing, just power/ground/network verification. GM is the same way, not sure about Ford. I believe you're right about sensor operation being very similar to air/fuel ratio sensors.

I've used rationality testing several times while catching lying NOx sensors. There's no rational way that NOx readings should be higher after the SCR, which means one sensor or the other is skewed. :lol:

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5 years 5 months ago #23970 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic NOx Sensor Testing?
Great post I have still to encounter these sensors but grabbing every bit of knowledge as Tyler posted everything I have found on them is saying normal visual, tug and circuit integrity test after that you are dependent on scantool. It did occur to me that the activating/closing the egr could be used as a test to poke the sensor output.

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



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5 years 5 months ago #23972 by Dieseltech
Replied by Dieseltech on topic NOx Sensor Testing?
I can’t anwser for dodge since I don’t work on them. But I have been dealing with nox sensors for years on heavy trucks. As far as I’m aware there’s no heater circuit on them, but I could be wrong. Like others have said you test for power ground then the can side of it. As for testing ,some manufacturers allow to run a low temp regen where they don’t dose fuel in to the exhaust if they have a 7th injector and don’t dose def so once the temps are up you can see if there both reading the same. But if they don’t I know Cummins on bigger engines has a scr efficiency test that will test nox sensors during it. But if they don’t have that is to force it in to a regen and view your nox sensors and see if they read weird . Someone else stated that the outlet shouldn’t read higher then inlet ,which is true sometimes but we have seen a failed scr will put out slightly more nox on the outlet then the inlet .

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5 years 5 months ago #23992 by gav09
Replied by gav09 on topic NOx Sensor Testing?
As far as I know all testing is done via scan tool. With no DEF doser operation both inlet and outlet should read close to each other. When the injector is activated outlet nox should drop at least 70%. Normally under steady cruise the nox sensor on a duramax or ISB cummins is around 200-300 ppm.
Here is cruising on a 2011 duramax.
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5 years 5 months ago #24012 by graywave
Replied by graywave on topic NOx Sensor Testing?
Thanks for all the replies everyone. Keep them coming. I appriciate all of them.

Where I work the boss sends diesels to the dealer or another shop even if its a simple MAF sensor problem such as on a Ford.

My Mobile diag business though I would like to have some diesel knowledge.

Confirm what it's not, and fix what it is!

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5 years 5 months ago - 5 years 5 months ago #24022 by Andy.MacFadyen
Replied by Andy.MacFadyen on topic NOx Sensor Testing?
The way I look at it modern electronically controlled diesel are a good starting point for learning how to deal with GDI engines as some of the technology carries over. Partly as a learning exercise I now run a diesel as my daily driver and actually quite like it, although engine access is a pita,

" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)



Last edit: 5 years 5 months ago by Andy.MacFadyen.

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4 years 6 months ago #33592 by katyjohn02
Replied by katyjohn02 on topic NOx Sensor Testing?
Hey,
Read this blog, here you can find detailed knowledge about these sensors
xenons4u.co.uk/blog/p229f62-p229e-and-p2...ror-codes-explained/

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2 years 5 days ago #55208 by Jibby101
Replied by Jibby101 on topic NOx Sensor Testing?
Sorry I’m a few years late to the party. However I believe I have some useful information on nox sensors. There are usually about 6-8 wires from the nox control module to the probe. The was the nox sensor works is like a maf sensor would be a easy understandable way to explain if the probe will heat up or cool down depending on the concentration of nitrogen oxides in the exhaust stream. There is a current increase or decrease proportional to the probe’s temperature fluctuations. Sonny putting a amp clamp around the signal wire between the probe and control module you can see if the current is responsive. However every manufacturer is different on wire color for the signal so finding the signal may be tricky. They do have a internal heater just like an O2 sensor. Once you find the signal you can scope the 1939 abs decode it find your nox sensors messages to the ecm when the nox increases or decreases see what your current does and take notes. How much current for how much nox. After working on the same aftertreatment systems a few times you’ll have the reading down to a science. The only other issue that you have to overcome is the signal is measured in ma’s so finding a good amp clamp that’s accurate in ma’s is crucial. Hope this info helps someone.

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