I have a 2012 Mercedes ML350 and I can not get the EGR Monitor to run. There are no DTC’s or Pending Codes. Any help would be appreciated

Is the check engine light on ? Any DTC'S - diagnostic trouble codes stored ? If any of these are true , light on or code's stored monitors will not set . Too set all monitors you do a drive cycle . A very specific way of driving your vehicle .

http://www.lyberty.com/car/drive-cycle.html

Try the manual

https://www.mbusa.com/mercedes/service_and_parts/owners_manuals

you cannot its a dealer only thing I have the same issue it costs around 30 pound for them to reset it some times you can buy reset tools from ebay cheap but don't always work

Duplicate question.

Hi there:

DTC P1400 - Differential Pressure Feedback Electronic (DPFE) sensor signal was below 0.2 volts. Enabling conditions: Run engine off or running self tests to check this code.

Blocking Action: This code can block the following monitors: Fuel Control, O2 monitor, catalyst, misfire, and EGR monitor.

Testing: Run the engine off and running self tests. If the code does not show up, it is an intermittent problem. Check for 5 volt reference that is low, damaged sensor or a short to ground in the signal wiring. Probes use an EGR position sensor signal which can be low because of a worn EGR pintle that drops too low in the EGR valve or for a warped EGR valve base.

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Rick,
The brake lamps on your Mercedes are computer-controlled. I would recommend scanning your computer network for possible fault codes.

p0400 is dead EGR.
and can fail 2 ways, stuck open or closed
if open engine wants to stall and lots of other DTC errors caused by EGR,
stuck closed, engine wants to PING
I'd fix EGR first, and not go broke finding shirt tail failures.
take it to shop let them fix it.
some times just cleaning the egr is all that is needed.
the other 2 codes are AFR lean codes
and if EGR bad or worse after 20 years, they EGR cracks and sucks air and engine goes lean.
I'd expect more things wrong and more DTC on any car this old.
for sure driven ******* the Autobahn.

Both of these monitors won't run until the oxygen sensor monitor has run. The oxygen sensor monitor won't run if an Engine Coolant Temperature (ECT) sensor Diagnostic Trouble Code (DTC) is stored. So, did you replace the errant coolant temp sensor? I take it you did and reset the codes. But you need to check the codes again and see if there are any that returned or are pending. A pending misfire code will not allow the oxygen sensor monitor to run. (Pending codes will not turn on the check engine light.)

This information is from Haynes Techbook "OBD-II" (No. 10206) Chapter 6, p. 14-16
(Highly recommended reading!)

P0146 pd means pending code
Pending codes and DTCs? Posted on November 12, 2010 by fcrmaster
When reading codes from your vehicle the fault code reader may show them as pending codes or normal Diagnostic Trouble Codes (DTC).
Pending codes (also known as continuous monitor codes) will be registered when an intermittent fault occurs. If that fault does not happen again after x number of start/stop cycles, the ECU will erase the code from memory. If the fault is persistent it becomes a DTC.
If you have read pending codes it is advisable to check the codes again after a week or so. If there is no apparent problem with the vehicle it is safe to erase the codes too and check back. But always make a note of any fault codes with the date and mileage of a vehicle.
If the codes read include a DTC then you need to investigate further. This you can either do yourself or advise your garage. If, again, you don't see an apparent problem (depending n the severity of the code) with the vehicle you can note the codes down and erase them. Then check again after a week or a few days depending on how often the vehicle gets used. If a repair has been made (previous owner) the DTC may just not have been reset after the repair.
The other numbers behind the code 01/06 , 02/06, 03/06 , 05/06 ,04/06 These don't mean anything . cheap code reader .
DTC P0140 HO2S Circuit Insufficient Activity Sensor 2
DTC P0146 HO2S Circuit Insufficient Activity Bank 1 Sensor 3
DTC P0171 Fuel Trim System Lean Bank 1
DTC P0174 Fuel Trim System Lean Bank 2
Sorry but this is something you should take to a qualified repair shop that has a diagnostic tool that can view sensor scan data.
Causes of lean condition trouble codes P0171 P0174 GM 5 3L

The DTC P0405 is for (Exhaust Gas Recirculation Sensor Circuit "A" Low)

DTC P0406 is for (Exhaust Gas Recirculation Sensor Circuit "A" High)

This would indicate a problem with the EGR valve sensor, or the EGR valve itself is malfunctioning.