EGR. Necessary evil?

Hello everybody.
I have a 2011 A6 Allroad Avant 3.0L diesel with 173000 miles on it. I bought it a year ago privately and I am very happy with it. This is my 8th Audi, my 2nd Allroad Avant.
Ever since I have had it, the EGR has been playing up with the MIL coming on. I get it switched off when serviced, but it comes back on after just a few journeys. I have had it diagnosed and it's showing a grade 3 fault with the EGR cooler/valve. (I was a VW/Audi mechanic some 50yrs ago, but these modern engines are beyond me!). I have used a few diesel cleaner additives, (Wynns, STP) which appeared to have worked, switching the light off, but only for a while. (My shortest journeys are usually 20 miles or more, I don't do short trips to the shops etc)
From invoices provided by the previous owner I can see....
The EGR cooler assembly was replaced in Sep 2022 (Parts cost £655.94) at 139691 miles. (This is the wording from the invoice)
A year later, Oct 2023 the EGR valve and cooler was replaced (Parts cost £707 inc VAT) at 153795 miles.
I don't like having the light on as I am concerned that if another fault is detected with something else, having the light on already will not allow me to see this, and it could be a more serious fault.
Another Audi owner (A4 3.0L 2010 similar engine) says that I could have the EGR system blanked off, so that it is no longer operating, and so would not keep switching the MIL on.
He has had it done to his by a garage and it runs fine. The EGR and valve is still in situ, but it's no longer operating. He said that as there was less carbonised air feeding back into the combustion chamber, less was getting back into the sump, via the rings and so his oil was less contaminated. He showed me his dipstick (!) and I have to say it was the cleanest oil I have ever seen. It was amazing.
It's my understanding that one of the main functions of the EGR is to reroute warm post combustion air back into the inlet manifold to get the engine up to operating temp more quickly. That seems like a good idea!
My questions are...
Is this a viable solution to the problem of the MIL lighting up?
Are there any consequences to having this work done?
Any help or information is greatly appreciated.
Thank you

The main purpose of EGR is to REDUCE combustion temperatures by mixture dilution which reduces the various oxides of Nitrogen production, commonly known as NOX, such as Nitrogen Dioxide… i.e. gases that kill living things. A quick search gives the following

Nitrogen oxides (NOx) harm life by causing respiratory and heart problems in humans, leading to lung irritation, asthma attacks, and increased mortality, especially in vulnerable populations. Environmentally, NOx contributes to the formation of photochemical smog and acid rain, damaging vegetation, reducing crop yields, altering soil chemistry, and affecting biodiversity in sensitive ecosystems. Some NOx, like nitrous oxide (N₂O), also act as a greenhouse gas and can induce short-term euphoria, but inhaling it in high concentrations is dangerous.

Effects on Human Health

• Respiratory Issues:
  Inhaling NOx can irritate and inflame the respiratory tract, leading to coughing, shortness of breath, and an increased susceptibility to respiratory infections like pneumonia and bronchitis.
• Aggravation of Existing Conditions:
  People with asthma or heart disease are particularly vulnerable to the adverse effects of NOx, which can trigger or worsen asthma attacks and increase mortality from cardiovascular and respiratory diseases.
• Severe Symptoms:
  High-level exposure can cause serious symptoms such as pulmonary edema (fluid in the lungs), chemical burns on skin and eyes, and, in extreme cases, a life-threatening situation due to inadequate oxygenation of body tissues.
• Mortality Risk:
  Long-term exposure to NOx is associated with an increased risk of all-cause mortality, as well as deaths from cardiovascular, respiratory, and non-accidental causes.

Environmental Effects

• Photochemical Smog:
  NOx reacts with sunlight and hydrocarbons to form smog, which reduces visibility and has the same irritating health effects as NOx.
• Acid Rain:
  NOx contributes to the formation of acid rain, which can damage vegetation, reduce crop yields, and alter the chemistry of soil and water bodies.
• Ecosystem Damage:
  Deposition of nitrogen from NOx can change soil chemistry, leading to shifts in plant communities and negatively impacting biodiversity in sensitive habitats.

Other Effects

• Nitrous Oxide: While other NOx are harmful pollutants, nitrous oxide (N₂O) is also a powerful greenhouse gas. Although used for medical purposes to induce a calm state, inhaling N₂O in high concentrations can cause serious health problems, including impaired cognitive function, nerve damage, and blood clots.

It'd be interesting to see what code or codes you are getting for the egr. Some restricted flow codes are due to carbon buildup inside the pipes

I only use recommended oil spec (VW 504/507 on mine) partly in the belief the acea rating (c2/c3) helps keep the egr from clogging.Another old wives tale theory I have is limiting excessive idle time. As turbos are accepted to let a bit of oil go into the exhaust at idle, limiting idle time makes sense.

Also no snake oils/additives as many are made for use in older petrols and can be harmful to DPF becoming extremely corrosive to some substances at high temperatures. The alloy egr on my model is extremely sensitive to water.

Hi Roverfan. Thanks for taking the time to reply. Appreciated. I have just come back from a 700+ mile trip and the MIL stayed on all the time. I am pleased to say that the car performed terrifically though. Previously when I have driven to London and the MIL was on, it has switched itself off after stopping at the services, and then set off again. I was informed at that time that it was an intermittent fault with a sensor in the exhaust pipe, something to do with checking the fuel mixture/burn. At least that's I understood of the explanation. I could be wrong. I was told that this current fault is a valve in the EGR not closing after the engine had warmed up.

Here's a section of the diagnosis the chap did for me. He's not a technician, but he's an informed enthusiast.

Address 01: Engine (CDY) Labels:. 059-907-401-CDY.clb
Part No SW: 4F9 910 402 A HW: 4F0 907 401 E
Component: 3.0TDI EDC17G000AG 0080

Revision: 16H14--- Serial number:
Coding: 0125002C190F0128
Shop #: WSC 01819 005 1048576
VCID: 2411E8DD92D6394ACAB-8070
VINID: 9D196AAAA1160D2780146209000CF9EAB9

3 Faults Found:
000306 - Oxygen (Lambda) Sensor B1 S1
P0132 - 000 - Signal too High - MIL ON
Freeze Frame:
Fault Status: 11100000
Fault Priority: 2
Fault Frequency: 6
Reset counter: 255
Mileage: 278733 km
Time Indication: 0
Date: 2025.09.16
Time: 11:45:02

Freeze Frame:
RPM: 1827 /min
Speed: 50.4 km/h
Lambda: 46.6 %
(no units): 0.0
Voltage: 1.000 V

001025 - EGR System
P0401 - 000 - Insufficient Flow - Intermittent - MIL ON
Freeze Frame:
Fault Status: 10100000
Fault Priority: 2
Fault Frequency: 10
Reset counter: 255
Mileage: 278808 km
Time Indication: 0
Date: 2025.09.16
Time: 17:14:08

Freeze Frame:
RPM: 1386 /min
Speed: 61.6 km/h
(no units): -19.0
(no units): 124.0
Inj. Quantity: 16.0 mg/str
Absolute Pres.: 1142.4 mbar
Temperature: 27.9°C

008597 - Oxygen (Lambda) Sensor B1 S1
P2195 - 000 - Signal too Low (Lean)
Freeze Frame:
Fault Status: 01100000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 278777 km
Time Indication: 0
Date: 2025.09.16
Time: 15:29:50

Freeze Frame:
RPM: 1092 /min
Speed: 33.6 km/h
Lambda: 44.2 %
(no units): 0.0
Voltage: 1.000 V

He was a bit confused that one fault says signal too high, and the other says signal too low.

When I have had the car serviced, the mechanic only used Audi recommended oil. I don't let the engine idle when I am stopped for any length of time. I have not used any more EGR/DPF fuel cleaners on it.

I hope this information is of some use to use, and that you may be able to assist with what I should do. I love this car, it would be nice to get the fault fixed, or the sensor bypassed. I am concerned that if another fault
was detected, I would not be made aware because the MIL would already be on. Thanks.

What is the VIN?

As a preliminary with those codes I'd visual check for intake leaks, exhaust leaks, and the wiring to the oxygen sensor. Looking for a large crack between intake to turbo, looking for evidence of oil turbo to engine, and soot around early part of exhaust system.