'08 NCV3 3.0L Diesel - Temp Sensor Implausible Value?

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Ben Carufel

Member
Hey folks,

I had a check engine light on my '08 NCV3 3.0 Diesel which was coming up with MBStar as "B19/12 Temperature sensor upstream of DPF - implausible value".

I replaced the temp sensor just in front of the DPF, cleared the code, and now about 200 miles later I'm getting the same code once again (see photo below).

Is there *another* sensor that I'm not seeing in the diagrams that I should be replacing as well?

Thanks...

 
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Deleted member 50714

Guest
Not sure if you are aware this diagram or if this covers your MY. Just thought I'd share. Hope it helps.
 

Attachments

ptheland

ptheland

2013 144" low top Passgr
Since you seem to have a Star system available, what is the actual temperature reading of that sensor while the vehicle is running? And perhaps some of the other exhaust temperature sensors, as well.

There could be a bad wire from the sensor to the ... ummm ... the whatever it runs to. (Maybe the ECU?)

The temperature could be implausible when compared to some other sensor, and the ECU decided to tell you about the wrong one. (Not likely, but technically possible.)

There could be a leak in the hot side of the turbo or the EGR could be stuck partially open dumping too much exhaust and dropping the exhaust temperature lower than expected at that point.

There could be a partial blockage downstream from the sensor, causing the exhaust to back up a bit and raising the temperature at that sensor too high.

All of this is to say that a sensor showing an implausible value doesn't mean the sensor is bad. It just means that something is wrong, and points you in the general direction of the problem. You still need to figure out the exact problem.

If I were to make a WAG, I'd check the wire for a break or a short. Near the sensor end and near the ECU (assuming that's where the other end of the wire is) would be the first places I'd look. Next would be any connectors that are in that wire between the two ends.
 
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Ben Carufel

Member
ptheland said:
Since you seem to have a Star system available, what is the actual temperature reading of that sensor while the vehicle is running? And perhaps some of the other exhaust temperature sensors, as well.

There could be a bad wire from the sensor to the ... ummm ... the whatever it runs to. (Maybe the ECU?)

The temperature could be implausible when compared to some other sensor, and the ECU decided to tell you about the wrong one. (Not likely, but technically possible.)

There could be a leak in the hot side of the turbo or the EGR could be stuck partially open dumping too much exhaust and dropping the exhaust temperature lower than expected at that point.

There could be a partial blockage downstream from the sensor, causing the exhaust to back up a bit and raising the temperature at that sensor too high.

All of this is to say that a sensor showing an implausible value doesn't mean the sensor is bad. It just means that something is wrong, and points you in the general direction of the problem. You still need to figure out the exact problem.

If I were to make a WAG, I'd check the wire for a break or a short. Near the sensor end and near the ECU (assuming that's where the other end of the wire is) would be the first places I'd look. Next would be any connectors that are in that wire between the two ends.
Click to expand...
Good idea, I did pretty much just "throw the part" at this one, hoping that it would solve the problem. I will trace back on the wiring harness to see where that sensor connector runs. Hopefully if it's got a wiring issue, it's not hard to find.

I agree with you that it's not likely that the ECU is identifying the wrong sensor which is giving the implausible reading.

If there was a blockage at or past the sensor (at the DPF, basically), I would think the ECU would show a code for DPF pressure.
 
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Deleted member 50714

Guest
My two cents, prior to commencing diagnostic evaluations, begin by evaluating the battery. I cannot stress the importance of deligent battery maintenance, especially, when the battery is located, out of sight and out of mind, such as my 2015 Sprinter. A sub par battery could cause other problems. I noticed your vehicle is nine years old. How old is the battery? Is it the correct battery? Just bouncing ideas. Hope you share resolution of your issue?
 
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Ben Carufel

Member
Bobnoxious said:
My two cents, prior to commencing diagnostic evaluations, begin by evaluating the battery. I cannot stress the importance of deligent battery maintenance, especially, when the battery is located, out of sight and out of mind, such as my 2015 Sprinter. A sub par battery could cause other problems. I noticed your vehicle is nine years old. How old is the battery? Is it the correct battery? Just bouncing ideas. Hope you share resolution of your issue?
Click to expand...
Good point, thanks for reminding me. I have been having some battery issues -- both are OEM Mercedes Benz batteries but I've no idea of the age of either one as I bought the van used in 2013. I need to make a separate post about that, will do it now...
 
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Dr. Soot

New member
Looks like your running the Mercedes diagnostic, that being said if you click on the code it should take you to a couple steps to follow. Also will point out which sensor is giving you trouble.
The temp sensor you speak of should be way up the pipe, it's the one that's a pain to get to. 90 degree angle if that helps.
When checking those temp sensors start reading the temps with truck bone cold.
Hope this helps.


Sent from my iPhone using Tapatalk
 
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