What is this part going into exhaust pre-cat?

[Conor]

Hey guys,

I was under the car today and been checking out the sensor situation. I could recognise the Lambda/O2 sensors installed pre/post cat and that is fine.

Now, I don't have a pic but there was a third sensor or something installed pre-cat that I couldn't understand. It was covered up to the nines in heat shielding too which I didn't understand.

What would it be?

I currently have error codes for a temperature sensor pre-cat on both sides. Perhaps these were temperature sensors?

Can somebody explain their utility a little bit and help identify a part for me?

Actually.. I have been looking these parts up on WIS EPC and meaning to ask.. I have the following parts listed. The wording is a bit misleading.. I mean "control probe" and "diagnosis probe" has thrown me.

(1 of each) - The part number are all subtly different.

1. A0045424818 - Lambda sensor left control probe in front of catalyst.
   
2. A0045424818 - Lambda sensor right control probe in front of catalyst
   
3. A0035428518 - Lambda sensor left diagnosis probe behind catalyst
   
4. A0045420718 - Lambda sensor right diagnosis probe behind catalyst

I am going assume the front (upstream) is towards the back of car and behind (upstream) towards the front of car, based on direction of exhaust.

Any time I query any of these parts all I get is lambda sensors.

Example code..

Thanks for any help.

 

[Uncle Benz]

The exhaust temperature sensors are installed pre cat on a lot of those. They are much thinner than a lambda sensor, held in with a tube nut, and often have a 90 degree bend in them, but sometimes they are straight, depending on location

 

[Uncle Benz]

The lambda sensors before the cat are used to control the fuelling. The ones after the cat just monitor the cat efficiency, they don’t influence the fuelling, hence their diagnosis definition. You have them arse about face in your mind

 

[Conor]

The lambda sensors before the cat are used to control the fuelling. The ones after the cat just monitor the cat efficiency, they don’t influence the fuelling, hence their diagnosis definition. You have them arse about face in your mind

Thanks.. but what does that mean lol?

Anyway.. I have been doing some research and learned a bit more (no surprise there!).

I had been having trouble identifying the various sensors and locations in the car, while understanding most of the theory. In EPC I looked further along the exhaust diagram and found the EGT and NOX sensor. Please see this picture of my exhaust and where everything goes.

The final piece of the puzzle is to find the correct names for the two cats in the diagram..

..So one could safely assume that according to the error above, I will need to replace the EGT sensors. I mean they are upstream of a device that has a NOx sensor on the other side

Please excuse me while I learn all this stuff lol. Before I bought this E class, I had only ever just about checked and topped up the oil in my car so this is all one big adventure for me



P.S. I was starting to get super confused when reading on the Bosch and Denso websites that they had sensors that could read both O2 and NOx. It's all starting to fall into place now though..

Oh and here is an alternate view for those that might doubt there are threaded holes for the EGT and NOx sensors

 

[flowrider]

Those pics don't look like the exhaust on my R230. The secondary CAT looks identical to the primary CAT on mine.

 

[Conor]

Those pics don't look like the exhaust on my R230. The secondary CAT looks identical to the primary CAT on mine.

Oh sorry, this is the S212 E350.

 

[flowrider]

Oh sorry, this is the S212 E350.

Doh! The NOX sensor and EGR is the giveaway

 

[Conor]

Doh! The NOX sensor and EGR is the giveaway

Why?

 

[LostKiwi]

230s don't have NOx sensors.