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So before I start tearing apart my engine I wanted to ask for advice.
My problem is error code P0471 - Exhaust Pressure Sensor Range/Performance - its 2011 2.1CDI OM651
I bought new sensor but it did not help, reading of back pressure with just ignition is 1,5BAR and what is funny it is the same if the sensor is screwed into EGR or just hanging on the plug while plugged in
That way I excluded mechanical problems so I started looking into electrical ones. When I hook up this sensor on a table to external power source to GND and 5v I get 0,65V on PIN3. When I plug the sensor in the car i get 0,01V on PIN3.
That is why I want to verify if the connection is correct.
If I understand correctly:
B60/3 Exhaust back pressure sensor shares + positive and - GND with B5/6, B5/9 and B28/17.
B60/3 Exhaust back pressure sensor takes + from PIN11, GND from PIN39 and sends signal to PIN89 on CDI controller N3/28.
Now questions - what does those highlighted in red boxes signs mean ?
How do I check this sensor? By verifying what voltage it sends on PIN3 when I apply pressure ? Or do I need to verify it differently (oscilloscope?)
Is my general thinking regarding electrical problems within the wiring rather than mechanical problems correct ?
The best way to go about troubleshooting your DTC is to research your code and check live data with a scanner.
Getting deep into the wiring diagram may add to your confusion. It shows how everything is connected.
The hard part is figuring the root cause.
As per definition P0471 - This code is strictly concerned about the incoming signal from the exhaust pressure sensor not matching intake manifold pressure or ambient air pressure at key on. This can be an electrical circuit fault or it can be mechanical.
Measurement at key on of exhaust backpressure is 1,5BAR while ambient is as usual 1BAR so it immediately triggers this error.
I think any mechanical error is out of the question when I get the same 1,5BAR reading whether this sensor is in the exhaust or just dangling on the wire or in my hand.
The only other fault would be the sensor itself but I got two of those and both act correctly in the tests.
That is why I think the cause is in the wiring but I need some help understanding it
It "looks" like a standard 5V-reference sensor... I would expect the sensor to read atmospheric pressure with just the ignition ON. I'm assuming your getting the 1.5 bar reading from your scan tool? How about reading the MAP sensor value?
I'm not sure how this sensor looks, what about applying vacuum to it to see if you can get it to read down to 1 bar. Your going to find little in the way of direct experience with diesels in this subforum.
Where I need help most are the wiring diagrams and understanding them and maybe info based on the diagram if this is just regular voltage/signal sensor or resistance-based sensor or hall sensor or whatever :P
It looks like this
MAF sensor and ambient pressure sensor have a correct reading of 1BAR at ignition - this is the only code that is left in this car
Some of the details on factory wiring diagrams... only MB and its engineers know. We've had discussions regarding many electrical issues. Besides ground points, splices, connectors, module designations, wire colors and wire gauge. I have not seen anything useful to deciphering signal nomenclature, like: 5V, GND, Sig, LIN, +, - besides making educated guess that 5V on a sensor signal likely is the reference. Or GND means ground and Sig may refer to signal.
The reason I ask if this is a W212, is maybe its a common issue for specific model and you might get better answers from people with first hand experience. I see you have a Sprinter listed under your profile.
If you want to provide your VIN, we can certainly try to pull up Mercedes diagrams out of WIS.
Looking at the sensor, I'd try using a hand vacuum pump and a piece of tubing... apply a little vacuum and see if you can get the 1.5 bar reading to drop to 1. That would be interesting, if then you cleared the code and would it come back.
Those diagrams are from WIS I got the WIS program. A common solution for this error code is either the bad sensor or clogged exhaust which in my mind I eliminated both. Maybe there are more solutions in DAS/Xentry but I don`t have an MB scanner and those programs - only chineese Dephli and WIS :P
The engine is shared with C class, E class, Sprinter and other chassis from that era but it wasn't sold in the USA, but my VIN is WDB9066371S609996.
As for wiring diagrams, I found even a piece of explanation for them on the web but this is only an example, not a full-on glossary:
I was hoping for such explanation for my initial post
Anyway I will try to get myself such vacuum pump and try changing the reading.
In most cases a 5V pressure sensor is a ratiometric one.
Lowest is 0.5V and highest 4.5V and is a linear one.
If you are getting 1.5 bar when it is hanging in the air, it maybe a faulty sensor/s albeit you got 2 units. Are they original parts or aftermarket ?
Even if this sensor is absolute , it should read very close to 1 BAR at sea level when dangling in the air.
If no vacuum test system, use shop air and blow.... but not too direct, the voltage should swing up.
If you measure at 11 & 39 with and without sensor installed, did you get the 5V ?
Same question as above but this time measurement at 1 and 2, sensor connector wire assy side.
Last edited by S-Prihadi; Apr 7, 2021 at 07:22 AM.
So it appears that my car was a classic case of "somebody has been here before"
I checked the pins on the connector according to the diagram and they were ok but then I noticed that pin numbers on the connector did not match numbers on the sensor. (PIN 1 on the connector was connecting to the PIN3 on the sensor etc)
I called the dealer and they gave me a different sensor number than the one that was installed, I ordered the correct one this time, and lo and behold - readings were back to normal, and the check engine was gone.
Funny thing is that some poor guy was driving in limp mode due to an incorrect sensor since 2019.
So it appears that my car was a classic case of "somebody has been here before"
I checked the pins on the connector according to the diagram and they were ok but then I noticed that pin numbers on the connector did not match numbers on the sensor. (PIN 1 on the connector was connecting to the PIN3 on the sensor etc)
I called the dealer and they gave me a different sensor number than the one that was installed, I ordered the correct one this time, and lo and behold - readings were back to normal, and the check engine was gone.
Funny thing is that some poor guy was driving in limp mode due to an incorrect sensor since 2019.
this is a lucky ending! Sounds like a no name aftermarket part from autozone... 🤣
That said it means that sensor part does go bad in service 🤗
it maybe a faulty sensor/s albeit you got 2 units. Are they original parts or aftermarket ?
Happy ending indeed.
That is the problem with a repair/procurement done by others and then you assumed it was done properly.
Well, I seen simple dumb-azz mistake on yacht's DC wiring from the builders themselves and no one took notice for years... LOL.
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Wiring diagram understanding Help
Happy ending indeed.
