OM642 exhaust pressure sensor

[snoman]

I have a Chrysler 300C CRD with the MB OM642 V6 engine. The original exhaust pressure sensor failed at 32K miles and its replacement failed less than 18 months later (I think at about 36K miles). Both new sensors were supplied by an MB dealer. I wondered if perhaps the connector might have been the problem, so before fitting the third sensor, I tried cleaning the connector terminals with a switch cleaner. That was 3 1/2 yrs ago. Now at 45K miles, the mil light has come on with the same fault (P0471). However, the engine appears to run normally and I have managed to clear the fault with my TorquePro App. Should the fault return, I will try cleaning up the contacts again and checking the wiring. It may just be co-incidence, but the fault seems to occur shortly after replacing a glowplug, or more recently, the glowplug module.

Has any other owner experienced problems with this sensor? I haven't had problems with any other sensor.

When I bought the first replacement, I caught sight of the inventory screen on the sales desk and noticed that more than 2,000 of these sensors had been sold in the previous 12 months and that the type numbers had changed several times within this period.

 

[Wighty]

I have a Chrysler 300C CRD with the MB OM642 V6 engine. The original exhaust pressure sensor failed at 32K miles and its replacement failed less than 18 months later (I think at about 36K miles). Both new sensors were supplied by an MB dealer. I wondered if perhaps the connector might have been the problem, so before fitting the third sensor, I tried cleaning the connector terminals with a switch cleaner. That was 3 1/2 yrs ago. Now at 45K miles, the mil light has come on with the same fault (P0471). However, the engine appears to run normally and I have managed to clear the fault with my TorquePro App. Should the fault return, I will try cleaning up the contacts again and checking the wiring. It may just be co-incidence, but the fault seems to occur shortly after replacing a glowplug, or more recently, the glowplug module.

Has any other owner experienced problems with this sensor? I haven't had problems with any other sensor.

When I bought the first replacement, I caught sight of the inventory screen on the sales desk and noticed that more than 2,000 of these sensors had been sold in the previous 12 months and that the type numbers had changed several times within this period.

If this is the exhaust back pressure sensor that is back right of the turbo , I'm still on the original at 2009 with 95k . There is a small hole inside the sensor , try spraying this with cleaner to make sure the hole is clear . Worth 15 minuites to try it anyway .

 

[Botus]

what boost are you running and what fuel are you using
they seem to do around 10 years and 100k then die

 

[snoman]

Thanks for the replies. It is encouraging to note that they are capable of long life.
I still have the first two sensors and the holes seem quite clear with no build-up of soot, but I will check and clean the current sensor if the mil light re-appears. I have also noticed that the hole on the second sensor is significantly larger than that on the first.

I haven't checked the boost. Maybe I could do this with TorquePro? As for fuel, I have mostly used Shell V-Power or BP Ultimate from new, but sometimes using another brand (eg Texaco) of super fuel, when first preferences unavailable.

 

[snoman]

Well, the mil light has returned, been cancelled, only to return on subsequent start-up.
I will try cleaning the connector contacts, as that has worked before and if that doesn't work, I will try re-installing the previous sensor which had only been installed for 18 months and a few thousand miles.

I've just realised that this recurring sensor problem has only appeared shortly after I've removed and replaced the engine cover. The sensor (and cabling) are close to one of the push-on/pull-off mounts which secure the cover, so I will check the cabling in that area.

 

[Dean Fletcher]

My cars got a Om651 engine and has 2 exhaust temp sensors. One near the turbo and one upstream from the cat. Iv had both changed after i had a inlet manifold issue. The second one wasnt faulty it was caused by a dirty ECU plug. I only found this out after paying 200 smackers for a replacement sensor which didnt fix the job.

 

[snoman]

Temp (not pressure) sensors?

 

[Dean Fletcher]

Temp (not pressure) sensors?

All came at once for me had to change to lot of them. Within 6 weeks. ****** nightmare

 

[snoman]

UPDATE:
Treated sensor and connector contacts with switch cleaning fluid, cleared fault code with TorquePro and no mil light after several start-ups.

I noticed that the sensor connector and cable are very close to the lip at the end of the engine cover and could be easily knocked when removing/replacing the cover. However, it does seem strange that a slight knock could disable the sensor. The wiring to the connector seemed secure and there were no signs of chaffing on the cable harness.

 

[snoman]

Looks like I spoke too soon!

Current pre-used sensor has failed again. So cleaning process was short lived.

Had MIL light come on again today with P0471 code (pressure range). Installed 3rd brand new sensor with only 47,000 miles on the clock and cleared fault code. Maybe there is some other underlying fault - could my current low annual mileage (3K) be an issue? Apart from glowplugs and glowplug module, I haven't needed to replace any other engine components.

 

[Dean Fletcher]

Looks like I spoke too soon!

Current pre-used sensor has failed again. So cleaning process was short lived.

Had MIL light come on again today with P0471 code (pressure range). Installed 3rd brand new sensor with only 47,000 miles on the clock and cleared fault code. Maybe there is some other underlying fault - could my current low annual mileage (3K) be an issue? Apart from glowplugs and glowplug module, I haven't needed to replace any other engine components.

I cant imagine the low mileage would make an difference.

 

[snoman]

I'm trying to think of a rational explanation for needing to replace the first sensor at 32K miles and then two more within the following 15K miles. MB quality assurance, perhaps? They do seem to be selling quite a lot of them. Fortunately, the sensor is very easy to access at the top of the engine.

 

[dannyfiveforty]

I'm trying to think of a rational explanation for needing to replace the first sensor at 32K miles and then two more within the following 15K miles. MB quality assurance, perhaps? They do seem to be selling quite a lot of them. Fortunately, the sensor is very easy to access at the top of the engine.

Snoman, what was ultimately the outcome of this problem. I see it was several years ago now but my 150k om642 is having problems with this sensor and wondering about a underlying problem that could be the cause..

Many thanks

 

[Larkone]

snoman​

Member · From Surrey, England
Joined Mar 21, 2018
Last seen Apr 30, 2019

At 150K miles then it would be reasonable to assume it has just probably died of old age

 

[Wighty]

Snoman, what was ultimately the outcome of this problem. I see it was several years ago now but my 150k om642 is having problems with this sensor and wondering about a underlying problem that could be the cause..

Many thanks

If it’s the exhaust back pressure sensor next to the turbo , some haven’t failed , they just need carb cleaner to unblock the hole underneath that is gunged up

 

[ajlsl600]

Clearing that vent will be my 1st port of call when time comes. Looks like a great benz earner that sensor. And prob less than a fiver to produce.

 

[rich.g.williams]

I would suggest finding out more about how those sensors work, finding out how to power them up to do a bench test. Or even rig up a meter/scope test that you can run in the vehicle real time independent of the ECU. Any strange intermittent spiking pressure sensor readings would show up that way so obviously clearly. Like a dicky sound system microphone cable.

Also finding out what the error code is actually saying, is it saying that the controller has picked up an electrical wiring OC/SC situation (MB controllers seem to like keeping a look out for these types of wiring loop faults). Or is the error code saying that the sensor is reading an implausible pressure value.

With a little knowledge of the circuit you could electrically plug in a dummy in place of the sensor and see what the ECU feels about that. What I'm getting at is there's a chance its not a pressure sensor fault at all - just some set of circumstances fooling the ECU into deciding the pressure sensor output is implausible at some point.

Maybe its just soot in the exhaust!

As for that so called vent hole, worth working out if that's the inlet for exhaust gas to press the sensor or if its some sort of vent to atmospheric from behind the sensor, I think it would just be for exhaust gas to press the sensor in which case keeping the soot dry and tapping the sensor a few times might get the soot out.

Think I would be tempted to cut an old sensor in half with a 1mm angle grinder disk and see what's inside - probably a diaphragm that the exhaust gas pushes against.

Doesn't always pay to actually believe fault codes as if they were Bible commandments.

Don't have this engine so that's the extent of my input on this.

 

[alcmackew]

what boost are you running and what fuel are you using
they seem to do around 10 years and 100k then die

Had mine replaced in 2022 and yes its a 2012 and covered 100,000 klms! Spot on...

 

[dannyfiveforty]

I have fault code 2616. Control variation pressure too high.

 

[Botus]

split hose - is the clue "too much variation" and rubbish grammar - aka does it mean its all over the place !!!!