Cold idling issues accompanied by P0401 EGR inadequate flow

[bvlenci]

Greetings everyone,
It has been some time since I last visited the forum, but I am seeking assistance as I am exasperated by this issue. Lengthy article, but I want to provide comprehensive information.

The vehicle is a 2012 W204 C220CDI with 149,000 kilometres. It was operating OK until one morning when it exhibited rough idling and occasional stalling upon startup. Engaging the throttle while stuttering allows it to continue operating; otherwise, it stalls if left alone. While attempting to accelerate, the engine light illuminated, and the vehicle entered limp mode. The only problem number is P0401, indicating inadequate flow in the EGR system. I suspect this inaccuracy may be a symptom rather than the underlying problem, considering it emerged after the tough operation; nonetheless, I might be mistaken.

After around five minutes of warming, the engine operates correctly, although in limp mode. I have successfully reset the problem while the engine is warm and after many on/off cycles, temporarily exiting limp mode; however, it reoccurs after harsh operation from cold, resulting in a return to limp mode.

Measures undertaken so far after online investigation!
- Attempted to disconnect as many accessible sensors and valves as possible to identify a potential malfunction. This generates a new problem number that disappears upon reconnection, indicating that I do not believe I have identified one that is malfunctioning.
- I conducted an injector leak-off test, revealing little flow, although the output was rather consistent across all injectors, with two exhibiting somewhat more flow than the other two. I have only performed this with a cold engine, not with a heated one.
- Replaced fuel filter - no improvement seen.
- Installed a used injector rail from a breaker to determine whether the pressure valve or pressure gauge was defective; however, this did not result in any change. I had significant difficulty in starting the engine after doing this procedure, likely due to an air lock. The battery was depleted several times; however, I ultimately succeeded in bleeding the system by utilising a suction pump to draw diesel into the rail via one of the injector pipes.
- I subsequently concluded that the issue lay with the Quantity Control Valve/Flow Regulation Valve Y94, since the vehicle operates OK initially but begins to malfunction after around 30 seconds. Yesterday, I mostly focused on disassembling components to access and replace this valve, followed by reassembly. Significant carbon accumulation was present in the EGR pipe leading to the input manifold and throttle control valve, which I subsequently cleaned. I refrained from removing the EGR valve, since it seemed to be a much more arduous task and I was short on time.

The issue remains unresolved! It is performing identically. Rough idling and P0401 error after few minutes.

I have reached my limit and may need to consult specialists. I am reluctant to invest financially on the automobile due to its limited value.

Any assistance or guidance would be much appreciated!

One more inquiry - does anybody know which sensor activates the EGR inadequate flow error? I presumed it was the little component on the intake manifold next to the entry point of the metal EGR input pipe. It seems to be connected to a venturi orifice, which I verified was unobstructed after the cleaning of the manifold.

[ForumGuru]

I had the same code. Administered Wynn's Extreme Diesel Cleaner to the tank; the indicator light extinguished within 11 miles.

[bvlenci]

I have used diesel fuel system cleaning for around 50 miles in all my activities so far, with no discernible difference.
Did you experience rough operation as well, or just the error code?

[Motoman]

No one sensor or actuator directly triggers the inadequate flow problem. The program is, however, more intricate than that.
Each emission-critical system or component will undergo a plausibility assessment that utilises alternative inputs for cross-referencing.

The EGR flow is not monitored directly. At each operational position, the volumetric efficiency is established, enabling the calculation of the anticipated air flow into the engine. The actual airflow entering the engine as measured by the Mass Air Flow (MAF) sensor. EGR displaces fresh air in the engine; thus, if the MAF is less than the estimated flow, the difference is attributed to EGR. It measures the pressure differential between the EGR valve and its location, therefore ascertaining the expected flow via the EGR. If the flow exceeds that established by the MAF, it will indicate inadequate EGR flow.

By considering how a defect is identified and its implications, one may ascertain where to direct their emphasis. The fuel injection system is not the appropriate component to investigate for an EGR flow malfunction.

[bvlenci]

I pursued the fuel path due to the first symptoms, namely the harsh idling until the engine warmed, and the diagnosis obtained from Google. The P0401 code appeared thereafter, and I presumed this was a result of the erratic operation disrupting pressures inside the system.

This evening, I took it for another ride and, after many error resets, I now got a new fault: “P227962 - Leak detected in the intake air system.” The signal comparison is erroneous.

The P0401 code has been resolved. Unless P0401 appears while cold and P227962 manifests when heated.

Unless I have inadvertently created a leak when disassembling it to replace the Y94 valve!
I am uncertain if this would lead to harsh idling or stalling.

[Motoman]

I would consider how to ascertain if the erratic performance is associated with the issues you are experiencing. Experiencing two unconnected defects simultaneously would be unfortunate.
The absence of EGR will not result in rough operation; but, excessive EGR, particularly in cold conditions, may. Could it be that it perceives inadequate flow since the MAF does not decrease when the EGR opens, despite the EGR really functioning? Disconnect the EGR; you will get another fault, but is it still operating roughly when cold?

The live data allows for the examination of rail pressures, as well as the demands of the pressure and quantity control valves. Graphing them facilitates the observation of irregular behaviour.

[bvlenci]

Thank you. I lack access to Star; but, I now own an iCarsoft MB, which enables me to show pressures and other data. The fuel system pressures seem satisfactory; nevertheless, I have not plotted them throughout the rough operation to analyse the occurrences. I can interpret some pressures, but I am uncertain about the expected ratios between MAF, MAP, boost, and other parameters.
I will attempt to unplug the EGR to see if it alleviates the harsh idling. That is contingent upon my ability to access the connection, since the space is really confined.