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Discussion Starter #1
Onto another problem that I can use your expertise.

I have been getting a P2202 error code (CEL) on and off (mostly off) since I purchased the car a couple of years ago. According to what I read, P2202 is NOx Sensor Circuit Low Bank 1. Here is what I have checked:

1. Removed both the front and back NOx sensors on exhaust and both looked clean. I can see discoloration on the metal from heat, but not build-up.
2. Examined the wiring from the control module to the sensor and they all looked good.
3. Removed the ad-blu injector and that is clean as well. No crystal build-up anywhere I can see. I can smell the "sweet" ad-blu additive at the tail pipe so I'm pretty sure it is injecting that into the exhaust.

I seems to get the P2202 code whenever it is a damp day (like after a rain).

Here is what I'm unsure of. The car is a 2009 MB GL320 BlueTec.

1. Which sensor is "Bank 1"? Is it the one in front of the Catalytic Converter or behind it? Am I even looking at the right sensors (i.e. on the exhaust pipe)?
2. I read that if I replace it (sensor and control module) with a new one, I will need to get the car reprogrammed/adaptation with the Star tool. Is there any other way to do adaptation beside paying someone $150+ to hook up the Star tool to it?
3. I also read that I can just buy the sensor itself (part that screw into the exhaust pipe) and cut the old sensor off the current controller and replace just the sensor without the need for reprogramming. Anyone tried this and with success?
4. If I was going to spend $150+ for someone to reprogram it, should I just take that money and buy a tool to do it myself (and to do other diagnostic and reprogramming in the future)? Any recommendation on the tool around the $200 mark that will work with this vehicle?

Thanks
 

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Anyone find out yet if after you replace a Nox sensor if you have to 'relearn' anything or is it a regeneration only that's required? That I know my scan tool can do.

-Brendan
 

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Replacing Nox Sensor

I contacted one of the Nox sensor seller that "custom" made their own so they offered 2-year warranty. They said their sensor is plug-and-play so the vehicle should relearn on its own. Don't know how much stock I should put into that since in the very next breathe, they said if it doesn't, I can take it to a Mercedes dealer to have them reprogram it. I like the company because the one thing that I've brought from them for my Mercedes (replacing some of the components in the DEF tank--heater and DEF lever sensor) worked faultlessly and their instructions for the replacement were spot on.

In any case, I am awaiting a delivery of a Nox sensor part (just the part that screwed into the pipe). Supposedly, since i'm not replacing the control module, relearning is not needed. Just need to cut the wires and spliced in the new part. I figured I will try that first for $73.

My dealership wanted $711 to replace the upstream Nox sensor for me (I can remove and re-install one in less than 7 minutes). They also told me that I should let them run a diagnostic on it (+$173) beforehand to determine if the downstream Nox sensor may also need replacing, probably another $700+. I'm thinking that I have never seen the downstream Nox sensor thrown a code why would I pay for the diagnostic.

Anyway, I will follow up once I replaced the sensor.
 

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RockAuto sells the O2 (oxygen) sensors, which I think you are referring to, for this vehicle in a bunch of varieties, but the most expensive they got is $114. In any event, I would think that after replacing one a person would simply have to clear fault codes, which would take five minutes. I would buy an actual Mercedes part, not necessarily purchased from a Benz dealer, though, getting the exact part number that came with the car, then there would be no need for cutting and splicing of wires. I might add that if a Benz dealership were the only place to get parts or have service, then I would no longer own a Benz. The only thing I would want from a Benz dealership, would be information. Learned from experience.. The Bosch sensors the car came with are under $100 each.
 

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Took a while but the part finally arrived. Put it in first thing Saturday morning (the upstream Nox sensor). Had about 100 miles on it (start/stop engine 10 times). Thus far, no additional error. Will report back at the end of the week after I put more miles and start/stop on the car.

Note. Rockauto do not sell this sensor (I brought my off Ebay from China for $73). They do sell O2 sensors for this car but the plug is not correct. If you look at the picture, the black connector on the control unit (where I cutted the 8 wires) is not removable. I did unclip the wiring harness to slide it back (and it will slide back), it only show the wires going directly into the other half of the black connector that seem to be glued down to the metal control unit itself. If I could have removed the wires to replace it, I would have.

As you can see from the photo, the new sensor wires are much longer then you needed. I cutted my pretty close to the original one (maybe an inch longer). I also straggle my joints so the shielding/installation can be pull over them. I would have preferred to tint the wires and solder the together. Unfortunately, the solder will not stick to these wires. So I used the clear shink tubing that came with the unit to join them. There is a small, soft metal ring in the circle that collapse with the shrink tubing that wrap around the wire. I added the extra shrink tube (red and black in the pics) over the clear one for extra strength and protection.
 

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Discussion Starter #9
After a week of driving, probably over 500 miles and at least 20 engine start/stop, the front Nox sensor warning definitely have gone away (still have the old error code, P2202, saved in my OBD reader). Normally, if I was to clear the error, it will return after about 30+ miles. So I'm very happy with the result.

Unfortunately, during the week, the rear Nox sensor warning came ON (P2201). As far as I can recalled, never saw this code prior to last week. So I brought another sensor unit on Ebay, this time from an US seller and received it within 2 days. The box looked the same as the one from China (which took almost 3 weeks to arrived). The sensor unit is brand new, like the pictures. The only thing that is different is the US one come with metal sleeves to crimp the wires together and ordinary black heat sink tubes vs. the clear one with low temperature solder as those pictured above from China. When through the same procedure to putting them on and re-installed back onto the car. However, that haven't resolved the problem. Now I am getting two error codes, the P2201 (as before the replacement) and a message that the value it received haven't reach the minimum threshold. I am going to drive with these errors for a week or two to see if the ECM will adapt to the new sensors.
 
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