EGR failure, what next?

May 5, 2025

EGR Fault – What's Next? Symptoms, Error Codes P0400, P0401, P0402… and How to Diagnose It

The EGR (Exhaust Gas Recirculation) system is one of the key elements of modern diesel and petrol engines, designed to meet stringent exhaust emission standards, especially Euro 5 and Euro 6 .
Although EGR is essential from an ecological point of view, in practice, EGR failure is one of the most common causes of problems in modern cars – from loss of power, through limp mode, to avalanche damage to the intake, exhaust and DPF systems.

Below you will find a complete list of EGR error codes , an explanation of how the EGR valve works , typical causes, symptoms and practical diagnostic methods .

Most common EGR error codes – what do they mean?

The following DTCs are most often encountered when the exhaust gas recirculation valve malfunctions. These are the ones you'll most often see on a computer printout (P0400, P0401, P0402, etc.) and then type into Google.

1. Errors related to incorrect operation of the EGR valve

P0400 – incorrect flow in the EGR system.
P0401 – EGR system flow too low.
P0402 – EGR system flow too high.
P0403 – EGR valve control circuit problem.
P0404 – Incorrect EGR valve range/operation.
P0405 – EGR position sensor voltage too low.
P0406 – EGR position sensor voltage too high.

2. Errors related to the exhaust gas temperature sensor

P0410 – exhaust gas temperature sensor indicates an operating error in the EGR system.
P2031 – incorrect signal from the exhaust gas temperature sensor before the EGR system.
P2032 – signal from exhaust gas temperature sensor too low.

3. Throttle or airflow related errors

These errors are not EGR "directly", but they strongly affect its operation.

P0299 – boost pressure problem (indirectly related to EGR).
P0101 – problem with the air flow sensor (MAF) – disturbs the operation of the EGR.
P0105 – Intake manifold pressure (MAP) sensor problem.

4. Errors related to the EGR electrical control system

P0489 – EGR valve control signal low.
P0490 – EGR valve control signal high.
P2141 – EGR valve electrical circuit problem.

5. System errors related to EGR

P1404 – EGR valve stuck in closed position.
P1406 – EGR valve stuck in the open position.
P1497 – problem with EGR valve position adjustment.

6. DPF Errors Related to EGR

P242F – too high soot level in the DPF filter (often the result of EGR problems).
P2002 – insufficient DPF efficiency – possible cause is EGR damage.

7. Other errors related to the EGR system

P2413 – Incorrect EGR/DPF system performance.
P2457 – EGR cooler problem – incorrect performance.

How does the EGR system work?

EGR involves reinjecting part of the exhaust gases into the intake manifold so that they can take part in the next engine operating cycle.

The main goal of EGR

recirculated exhaust gases lower the combustion temperature in the cylinder,
lower temperature limits the formation of nitrogen oxides (NOx) ,
This is particularly important in modern diesel engines operating on a lean mixture (lots of air, little fuel).

Exhaust gases introduced by EGR:

are "sterile" - they do not actively participate in combustion,
fill part of the combustion chamber, reducing the amount of oxygen,
They lower the combustion temperature, which can reduce NOx emissions by up to 90% .

Types of EGR systems

There are several exhaust gas recirculation architectures in modern engines:

1. High Pressure EGR (HP-EGR)

classic, older type of system,
takes exhaust gases directly from the exhaust manifold , before the DPF/catalyst,
uses the exhaust gas pressure generated by the turbocharger to force it into the intake.

2. Low pressure EGR (LP-EGR)

collects exhaust gases after the diesel particulate filter (DPF) and catalytic converter ,
thanks to this, the exhaust gases are much cleaner,
are directed in front of the turbine ,
Due to the lack of back pressure, a throttle valve is used in the exhaust system, which can close by up to 70–80% , forcing overpressure and exhaust gas flow to the intake.
this system is used, among others, in newer Audi 2.0 TDI engines (Dead/Deta codes) for further ecological optimization.

3. Internal exhaust gas recirculation (Internal EGR)

mainly in petrol engines, e.g. TSI, FSI ,
implemented using variable valve timing (Vanos/phasors),
By appropriately delaying the closing of the exhaust valves, some of the exhaust gases are "sucked" back into the cylinder.

Components of the EGR system

The main components most often involved in EGR failures are:

EGR valve
– a flap or mushroom regulating the flow of exhaust gases.
– in older cars controlled by vacuum, in newer ones – electrically.
Exhaust gas cooler (EGR cooler)
– cools the exhaust gases before they enter the intake,
– cooled exhaust gases occupy a larger volume, which allows for more of them to be injected and the combustion temperature to be lowered more effectively.
Intake throttle (extinguish flap)
– in diesel engines it may close the intake while the engine is running,
– artificially creates a negative pressure that “draws” more exhaust gases into the intake manifold.

EGR failure – causes and symptoms

In practice, an EGR failure is rarely a problem in itself. It is usually the result of :

negligence in servicing,
poor engine condition,
problems in the intake / exhaust / turbocharger.

1. Carbon clogging (the most common EGR failure)

This is the most typical problem with diesels.

The exhaust gases from the EGR, forced into the intake manifold, are mixed with:
- oil mist from the crankcase vent ,
- oil mist from the turbocharger .
a thick, sticky mass is formed – carbon deposits .

Effects of carbon deposits:

a collapsed intake manifold and valve stems restrict air flow,
cylinder filling deteriorates,
combustion becomes inefficient,
loss of power and increased soot production occur,
Carbon deposits on valves can cause them to leak.

Impact on DPF:

improper combustion = more soot,
the diesel particulate filter (DPF) gets clogged faster and regenerates more often,
the risk of errors like P242F, P2002 increases.

2. Mechanical failure of the EGR valve

The EGR valve may be mechanically stuck:

in the open position,
in the closed position.

EGR stuck in open position:

the engine smokes, loses power,
there may be problems with starting,
In extreme cases, the engine may not start.

EGR stuck in closed position:

the engine operates at a higher combustion temperature,
NOx production is increasing,
the symptoms for the driver may be less clear - errors are recorded in the controller, and above all, the environment and DPF operation deteriorate.

3. EGR cooler failure

EGR coolers operate in extreme conditions (high temperature, large thermal differences), which makes them susceptible to:

cracks,
leaks,
microcracks leading to coolant leakage.

Symptoms of a damaged EGR cooler:

coolant intake without visible leaks,
fluid may be entering the intake,
Therefore, today, when drawing coolant , the EGR cooler/water intercooler is often checked first , before any head damage is suspected.

EGR diagnostics – how to check EGR with a computer?

EGR system diagnostics are closely linked to air mass measurement. The engine control unit (ECU) calculates the amount of recirculated exhaust gas based on the fresh air drop measured by the mass airflow sensor (MAF).

1. Interpretation of actual values (e.g. Group 3)

The most important parameter is the value from the air flow meter (in mg/stroke).

EGR efficiency at idle:

when EGR is open, the air flow (mg/stroke) decreases because part of the "volume" is occupied by exhaust gases,
for example in a Passat with unit injectors:
- with EGR open, flow: approx. 250 mg/stroke ,
- with closed EGR : approx. 500 mg/stroke ,
- a decrease of approximately 50% is correct.
in other diesel engines, typical flow with EGR open is approximately 250–280 mg/stroke .

Blocked/blanked EGR (closed mode):

if the EGR valve should be open according to the controller,
and the MAF reading is close to the value for closed EGR (e.g. approx. 500 mg/stroke),
this means that recirculation is:
- closed,
- blocked,
- blinded.

In such a situation, the driver may report an error such as:

"EGR flow rate too low" (e.g. P0401).

2. Visual and mechanical verification

Since EGR is often only an “end result”, diagnosis must cover the entire system :

Intake manifold condition
– whether it is not covered with carbon deposits.
– in modern petrol engines (e.g. 1.5 TSI ), heavy carbon deposits on the valves may indicate problems with internal recirculation and direct injection.
Diagnosis of pneumothorax
– whether the crankcase ventilation system is working properly,
– whether it does not release excessive amounts of oil mist into the intake (one of the main components of carbon deposits).
EGR execution tests
– in older vacuum systems, the valve can be tested by applying a vacuum,
– in newer ones – checking the electric control and valve response,
– in vacuum systems (e.g. older Passats), a leak in the vacuum line may cause simultaneously:
- EGR failure,
- turbocharger problems.

What next after detecting an EGR fault?

1. Repair and prevention – recommended direction

The best solution is to repair the system and remove the root causes of excessive soot and carbon deposits.

Key activities:

Frequent oil changes
– avoiding Long Life intervals (30,000 km and more),
– shorter intervals improve engine cleanliness and reduce carbon deposits.
Replacing seals under injectors + inspection/regeneration of injectors
– leaking injectors generate excess soot.
Cleaning the intake system from carbon deposits
– intake manifold, valves, intake channels.
Turbocharger check
– undercharging / overcharging disturbs combustion and increases soot production.
EGR cooler repair
– when drawing coolant, damaged EGR coolers (or water intercoolers) must be replaced .

2. Software modification - EGR disabling

Many users – especially in older or heavily used cars – decide to program the EGR from the ECU when:

repair costs are high,
the car is driven mainly outside the city,
recirculation generates frequent problems.

Legal and ecological issue:

EGR is an element designed to meet environmental standards,
removing the system that limits NOx emissions is inconsistent with the manufacturer's assumptions and regulations ,
From a legal and ecological point of view, it should not be removed.

DPF connection:

Completely disabling EGR during the normal operating cycle can:
- worsen the efficiency of DPF combustion,
- make regeneration more difficult in city driving,
EGR helps maintain the appropriate exhaust gas temperature needed for DPF regeneration.

“Optimization” solution:

it is possible to modify the software in which:
- EGR is disabled during normal driving (less carbon deposits, cleaner intake),
- but remains active during the DPF regeneration procedure ,
such modifications should be considered as "track/off-road" solutions and not for driving on public roads.

Overall: if you see errors like P0400, P0401, P0402, P0403, P0404, P0405, P0406 on the computer, the car smokes, loses power or the DPF starts to clog - do not stop at just "clearing the error".
You need to check the air flow, carbon deposits in the intake, the pneumatic valve, the EGR cooler and the DPF – only eliminating the cause will provide a lasting effect and protect the engine and the entire exhaust gas aftertreatment system.

Back to blog