AnchorMgmt

Here's a copy of the sensor pic from the manual.

While I haven't changed this sensor yet, I have noticed that the $18 IAT sensor that I changed has done some good. I was perpetually going into limp mode prior to changing that one out (it kept getting worse). I know I need to change this pressure sensor (@dpf), but at least something I did helped it along until the part arrives!

N_Jay

Were you getting any codes with the IAT sensor limp mode?

AnchorMgmt

I did not. Here's a summary of my GL limp mode journey...

1) I originally got the P1402. Painstakingly cleaned EGR. While there I changed air filters and did thorough engine cleaning (fuel filter and oil was just changed) weeks before.

2) Read about the diff pressure sensor being the silver bullet. Located the wrong part and changed it (MAP sensor). After changing MAP sensor I began throwing MAP sensor code P0069...go figure!!

3) Researched MAP sensor across all diesel makers, came to conclusion that MAP issues are usually related to IAT issues, as well. It was cheap, I have time, so I changed that sensor. It was really easy to change.

4) Changed battery as I realized it was the original and I prefer AGM (great experiences with AGM powering big stereo in my boat). Battery change was a super PITA.

5) Still in limp mode (b/c I didn't change dif pressure sensor) and still got P0069 CEL. That's when I realized that I never got a P0069 until I changed it! I cleaned old one and reinstalled it. GL was up and running w/out limp until I got to the dealer later that day. BTW..I got full refund on defective OEM MAP that I had installed.

6) Dealer read codes and quickly diagnosed as same problem with a GL320 he had just fixed a week before...the pressure differential sensor at DPF. He mentioned something regarding the codes he was reading and also the idle at startup (mine was revving high, dropping fast, etc.). Dealer didn't carry part in stock, so I opted to drive her home and fix it when the part comes in (neighbor has a lift...very sweet).

After EGR clean, it would still go into limp mode immediately. After the IAT change, it actually has been running pretty well. Besides the one time the other day at the dealer, it's running normally...no limp mode. BTW...mine runs and shifts seamlessly and powerless in limp mode. Mech said the other one he just fixed shifted horribly in limp, but the sensor resolved issues.

I'm looking forward to installing the dif pressure sensor and not thinking about limp mode again...hoping the GL will be "strong, like bull!"

N_Jay

Mine has been in Limp mode about 6 times over the last year.
Most have either been cold or wet weather. (Maybe both?)
Restarting has always cleared the limp mode.


Mine runs really well in limp, (the first time it happened to my wife, she did not even notice at first.)


I have only had it connected with a CEL once and that was a Sub zero start that almost did not start. Received the EGR and Low Rail Pressure codes. (ODB/CAN reader only)


Cleared and have not come back.


I have seem several places on line where the DPF pressure sensor part number mistakenly comes back to a MAP part.


Figure if we all keep sharing our experiences, maybe someday we will get a definitive diagnostic process for finding the right fix.

AnchorMgmt

Just changed the differential pressure sensor at DPF. It was really straight forward and easy to access in the center of the vehicle. Here's what it took:

1) unplugged sensor
2) removed nut holding sensor on (10mm)
3) removed nut holding hoses (8mm)
4) pulled sensor with hoses connected down to make easier to work on.
5) removed old hose clamps, installed new ones.
6) put everything back together.

Happy trails...

a2j

Did this on Friday night. Working great for 3 days now. Left the car overnight outside for couple of nights. Temps were near 0F.
Part number that was on the old sensor that I've removed: A 006 153 49 28
"New" part number that was shipped to me: A 642 905 01 00

dgiturbo

You are all welcome.

a2j

I still would like to know what exactly caused it. Poor quality sensor? Millage? Cold temps? It can't be just the battery. I'm not even at 100k miles yet. What about others?

N_Jay

I am guessing the sensor is degrading.


It is not in a nice environment.


It would be nice if it set a code directly linked to that sensor or circuit when it goes into limp.


It also seems to be set on startup.
Has anyone had it enter this limp mode while driving?
There is a lot happening during initial start up.
Voltages are fluctuating, pressures are stabilizing, etc.


If the sensor is a piezo element the voltage being measured may be very small, it could just take a little salt on the wrong connection to throw off the sensor reading.

efzauner

I doubt that this is the case. These sensors are not connected to the battery, they are connected to various Electronic Control Modules. These have their own on board voltage regulation systems that shield the electronics and sensors from the messy battery/alternator/starter circuits.

efzauner

Help with the acronyms please!
IAT: Intake Air Temperature sensor?
MAP: Manifold Air Pressure?
not to be confused with
MAF Mass Air Flow
DPF Differential Pressure Sensor on the Particulate Filter?


Thanks

N_Jay

Yes, but low and noisy supply voltages can still cause transient effects.
These machines are well designed but not perfect.

N_Jay

I think you have them right, but I find them misnamed on parts sites and in discussions.

kolyanich

I had the famous P1402 code come up on my ML320 CDI. Came across this thread. I didn't even bother trying to do anything with the EGR or anything else, as some of the earlier posts suggested. Replaced the diff pressure sensor per dgiturbo advice. Code went away, no more limp mode.

bha

When I got that code, it said it was the DPF pressure sensor, so I bought the sensor and replaced.


I had been resetting the check engine light and it work work for a day, then turn on again. Figured the sensor was dead.


Fixed the problem. Same thing you guys are reporting.. no more check engine light, no more limp mode, etc.


So if you're getting that code, odds are the sensor replacement will fix it. Note that they are "CLIC" type clamps same as the fuel filter. They are supposed to be removed with a special tool and replaced (MB says don't reuse them). I was able to get them apart and back together with needle nose pliers, but if I were you I would replace with a regular hose clamp (gear style). Or get the tool (which I now own) and a new set of clamps before you start the job.


It was a 10 minute replacement job. Raise the air suspension all the way and shut off the truck. Make sure the exhaust isn't hot so you don't burn yourself (do it from a cold start, not after you have driven the truck..).


Simply disconnect and replace. Tighten the new clamps and you're good.


You can crawl under the truck from the side and see the sensor clearly. If you have seen a pic of the part (or have the new one in hand) you will know exactly what to look for.


Additional (possibly useful) info: Dealership where I bought the part said they replaced 2 in the last week. It seems to be quite a common failure on diesel ML/GL models according to the parts guy. He said they keep a lot on hand because they go through them quickly.


$92 Canadian.. I'm sure much cheaper in the US. And probably even cheaper online but I was in a rush.

finnmerc

Hi All,

Greetings from Scandinavia.

Last winter my R320 CDI had power-loss with code p1405 few times. It happened first at cold weather (at 20F), which seems to be common. This was not a big problem, as simple code reset cured the problem for the next couple weeks. And it happened only few times anyway. When spring came I had no issues.

This summer problem came back, but this time it was P1402. Now it happened when starting hot engine. This time the problem turned into real nuisance, as it kept appearing every day.

After reading this thread, I had EGR valve cleaned. No change, still the same thing. Then I got a new pressure difference sensor, which appeared to be stock item at local dealer. Replacement took like 15 minutes, and now I have had no problems for a month. I guess it was the sensor!

Thanks a million for everyone in this thread, you really made it easy for me to troubleshoot and fix the issue! If I relied on the code only, I would probably have replaced EGR valve next, which would have been 550€ + labour instead of 70€ for sensor and 15 mins of quality time with my car

Thanks!

iulianpopa

hi to all of you,
somebody have some picture with the location of this sensor?
is under the car close to the diferential?
thx

bha

Hard to explain, but it's an easy sensor to find.

Raise the truck all the way (using the "raise" button on the dash).

Crawl under the truck half way between the front and back wheel, on either side.

When you get to the middle of the truck, look at the underbody. Along the exhaust pipe you'll see one of the "mufflers/resonators" and the sensor is hanging right beside it.

It has a few rubber hoses connected to it, and also an electrical connector.

When you're underneath the truck in the very middle, looking straight up, it's the only thing there aside from the exhaust pipe.

10 min job to replace. You need special pliers for those clamps, and also I believe MB doesn't want the clams re-used so you need new ones. Or you can cut them off and use regular hose clamps.

Use stainless steel clamps otherwise they'll rust. I find that if Home Depot doesn't have them, go to a West Marine or other boat store and buy two there.

Remove clamps (or cut off with end cutters if you don't have the tool), disconnect electrical connector, then swap sensor and reconnect everything.

Mine failed 3 years ago when I bought the truck (it was probably bad before I got the truck, not sure) and then again a year ago. I think they keep updating the part because the original, first one and second one on my truck all had different part numbers. First one failed on a hot summer day (may have already been bad) but second one failed on the coldest day of the winter, which I believe is when they usually fail.

Of course I have put 60,000 miles on the truck since I bought it, so I now consider them more of a 'wear' part or maintenance item. If it goes again in 2 years I'll just buy another one. Hopefully the one on the truck is good for a while and 'permanently' fixed by MB but you never know.

I haven't even jacked up the truck to change it at all.. just raise it with airmatic and crawl underneath.

iulianpopa

thanks a lot

jenxo

I see this part on ebay and ECS tuning. Is this the right one?

http://www.ebay.com/itm/Dodge-Freigh...ZXR~pl&vxp=mtr

https://www.ecstuning.com/Search/Sit...sor/ES2666639/

-Jenx

iulianpopa

this is the sensor, changed and everityhing it s gone be ok, easy to replace