dpallone

Twice over the past week when the temperature was below 20 degrees F, the truck would accelerate very slowly and lose speed on steep hills. As soon as the temperature went into the high 20s and I restarted the truck, the issue went away.

The first time, the check engine light came on. I went to a local service station and they read the code as P1402 and cleared the code and check engine light. The second time it happened, the check engine light never came on.

I have to wait for the temperatures to drop again to take to my dealer so they can duplicate the issue.

Did anyone experience this and what was the issue?

mtrevelino

This is the only thing that I found that is mercedes related:
http://www.benzworld.org/forums/w901...ode-p1402.html
Mike T.

alx

you can start by cleaning/ replacing your egr valve. they do gum up and with cold weather it gets worse.

it is in the driver side back of the engine

here is a pic from behind

#4 is the hose that goes into the egr valve. it is held by two bolts.

lisischeff

I have the same exact problem...2 weeks ago I pulled code 2078-8 pressure differential sensor. we cleared code and all was good till a trip to NH this past weekend..cold cold..limp mode, then shut off, wait a bit then full power upon start up...Im ordering a pressure differential sensor...let me know how you fare

alx

i believe you and the op have different problems (and solutions) based on the codes pulled.

dpallone

Due the the recent severe cold weather in the Northeast, I was able to recreate the situation. The temperature was 8 degrees F and I left it parked outside overnight. Starting in the morning, the truck would not shift at higher RPMs and felt like it was in what is referred to as the limp home mode, very slow acceleration. The check engine light came back on.

My independent mechanic read the OBD fault code P2078 which is the pressure differential sensor. The sensor was replaced and the problem has been resolved as of this morning when it was 10 degrees F outside and I tested it again.

N_Jay

You searched for: P1402

The following results were found:
Mercedes Benz: Exhaust gas recirculation open-loop control
BMW: Heated Catalyst Power Switch Overtemperature Condition (Bank 1)
Daihatsu: TPS 2 open or short circuit
Fiat: Flap
Fiat: Ventol EGR throttle valve
Ford: Exhaust Gas Recirculation Metering Orifice Restricted
Kia: EGR Control Solenoid Circuit Signal High/EGR Valve Position Sensor Circuit
Mazda: EGR Valve Position Sensor Circuit
Nissan: EGR System Fault Detected
PSA: EGR Metering Orifice Restricted
Subaru: Fuel Level Pressure Sensor Circuit
VW: EGR Valve Circ Short to B+

You searched for: P2078

The following results were found:
Mercedes Benz: Read fault memory from control unit N15/6 (Sprintshift control module) and rectify faults.
Standard DTCs (ISO 15031-6/SAE J2012): Intake Manifold Tuning (IMT) Valve Position Sensor/Switch Circuit High Bank 1a

lisischeff

so my problem was intermittent..only when it was super cold did i get limp mode..but as the day warmed up and the car was shut off for a short bit...full power always returned...until the recent sub zero temps...CE light and if the car was shut off for 20 min in the frigid outside the car spent the day in limp mode...UNTIL...I replaced the pressure differential sensor in the transmission tunnel 3 days ago...the replacement was a snap and it has now been 3 days of no problems in super cold temps...all is good...thank you all for your help

a2j

Getting a limp home mode when its cold outside. Restarting the engine after 20mins of driving does not trigger the CEL because code clears itself. CEL shows up if engine has been running for a short period of time in cold/freezing temps. P1402. Should I be looking at EGR valve or this differential sensor? Where is this sensor?

AnchorMgmt

I had similar limp home mode experiences up to last wknd...when it was more frequent and threw a P1402. I had mistaken it for bad fuel, as restarts following Howes seem to fix it. I was mistaken!

I took off the EGR valve and gave it a good cleaning. I also changed the MAP sensor. Is the MAP sensor the same thing as a differential pressure sensor? After all this troubleshooting, it's still happening. Now it's throwing a P0069 code today (after I put the new OEM MAP sensor in).

I read in other posts that it could be the charge pressure sensor. Is that the same sensor as an air intake/charge temperature sensor?

Any help is much appreciated. Thanks!

AnchorMgmt

I've been using mbpartsworld.com for parts location on my GL. The pressure sensor (MAP) was located on the passenger side front of the motor. It was simple to change (2 screws).

I'm unsure if this is the same part as the "differential pressure" sensor. On the 2009 GL320 parts blowout, it's literally the same part image in the same location as the 2008 images.

Here's the URL to mbpartsworld image (part #095): mbpartsworld pressure sensor

dgiturbo

The most probable cause of limp home and code P1402 showing on an aftermarket code reader is the differential pressure sensor located in the exhaust near the DPF. Have your dealer or an indie with a Star diagnostic software check the codes. You will learn that it will be a low voltage plausibility reading.

My theory is that as the severe cold weakens the battery, and as we get in the vehicle to start it, several electrical consumers power up, so by time we crank, the battery has taken a sucker punch. The differential pressure sensor reads the dip in voltage as a particulate filter restriction, and triggers a check engine and the ECU puts the vehicle in limp home. Like anything else, the sensors are much older and have probably over 100K miles on them, so the accuracy slips. (Just like the O2 sensors on gas cars need to be replaced every so often.)

The pressure sensor in the front of the motor is an intake pressure sensor. Not the same.

AnchorMgmt

Thanks dgiturbo. Do you know where I can find an image of that part on the motor? I've looked everywhere and keep coming up with the pressure sensor on the front of the motor.

I changed the battery today. Since it was the original OEM one, it was time!

Thanks folks.

N_Jay

My P1402 has not come back since that one long crank in sub-zero temps.

a2j

My battery is 2-3 month old. Are you saying that GL isn't compatible with cold temperatures?

N_Jay

It all depends what you mean by "compatible".

No diesel runs with jelled fuel.

Just because your battery is new does not mean everything else is within spec.

a2j

My point is that the battery, weak or new, doesn't really have anything to do with this issue.

N_Jay

Yes and No.

If the sensors are throwing codes due to low voltage as opposed to an actual out of spec measurement, it could be due to a longer than expected crank due to degradation and wear of other parts.

The better the battery (and connections) the better it will supply an acceptable voltage for a longer the normal cranking period.

The Honda Pilot (my previous car) is famous for odd error codes due to old batteries, bad battery connections (and grounds) and they often show up during/after long cranks.

kerlyb

Was it difficult removing EGR valve? Any tips before I start this project?

AnchorMgmt

AGM battery change did nothing for my issues. Originally it was a P1402, now it's a P0069. I changed the MAP sensor (P0069) w/brand new OEM sensor so it's just a symptom now. I've got the air temp sensor I'm going to throw at it before I take it to the dealer and raise the white flag. I just can't figure out where that beast is hidden!

This post was helpful for EGR removal: http://www.benzworld.org/forums/w164...300-p0671.html

However, from what everyone else has seen, including me, that was not the fix. It gave me piece of mind, however it was a knucklebusting effort. Good luck!

AnchorMgmt

Went to the dealer for deep diagnosis. As many have already stated...it's the pressure differential sensor (at the DPF). The other codes he read were just symptoms of this issue. I have the sensor on order and will replace this weekend. My mechanic said he just changed the same sensor for another 08 GL320...all the same symptoms.

Thanks for everyone's help on this forum. Next project...flushing the front diff!

N_Jay

Any idea how they determine a failure of the DPF Pressure Differential Sensor, verses an actual high differential pressure across the DPF?


I am thinking that as these cars get older the DPFs may be getting to the point they need to be properly cleaned above and beyond what a regen cycle does.


There is an entire industry popping up to recondition DPFs.


http://www.dieselservicecenter.com/dpfcleaner/
http://www.dpfregeneration.com/Services.html
and others.

a2j

And you have a part number and the location of this sensor?

N_Jay

Looks like A0061539528


I can't tell where it is mounted from the EPC pictures.


Just follow the lines from the DPF.


EDIT:
Found this
http://workshop-manuals.com/mercedes...ons/page_5626/


Location
The differential pressure sensor (DPF) is located in the left transmission tunnel at the transmission output flange

AnchorMgmt

My mechanic gave me the same part number. I provided my VIN and got the updated part number when ordered. It's gone through a few changes. Ordered mine from Benz Parts Wholesale. They were very helpful, I'll know more about product once it arrives Friday. Mechanic also gave me a nice printout of the part on the vehicle. I'll scan and post tomorrow.