Audi SQ5 P0402: EGR Flow Too High

Hello everyone,

I'm currently working on an SQ5 that's showing an error code indicating that the EGR (Exhaust Gas Recirculation) flow rate is too high. This error usually occurs during high-load driving, which then puts the vehicle into limp mode.
According to the freeze-frame data, the error occurs during thrust operation.

Model: SQ5.
Year of construction: 2013.
MKB: CGQB
Mileage: 189,401 km

I performed a logging run until the system entered limp mode, and I have graphically represented the SETPOINT/ACTUAL values of boost pressure, air mass, and EGR valve in the attached document. The blue graph shows the SETPOINT value, and the orange graph shows the ACTUAL value.

Are the cause of the error visible based on these measurements?

Thank you in advance!

Hi,

It would have been great to have Autoscan and a log with load, air mass target/actual values (instead of just images).

If the EGR valve is stuck open, it may not close properly. Alternatively, there might be an air leak somewhere after the mass airflow sensor (MAF), such as in the intake manifold or the charge air cooler, causing unmeasured air to be drawn in.

Best regards, Rainer.

I just quickly glanced at the pictures.
The significant discrepancy can be seen in the last image (the air mass should be/is). The boost pressure in the image before that is correct.

However, the actual air mass is far too low and significantly below the target air mass.
Because not enough fresh air is being drawn in, the engine believes it is inhaling too much exhaust gas, leading it to interpret the high EGR rate as a fault.

I would either say the cause is...
A) In the case of a stuck-open EGR valve, there is a suspicion (of a truly excessive EGR rate) or...
B) Air leak (behind the mass airflow sensor) (= correct exhaust gas recirculation rate and correct amount of fresh air entering the engine, but the engine control unit is misreading the data).
C) due to soot deposits in a completely sealed intake manifold (in this case, not enough fresh air will enter even when the EGR valve is closed).
D) The DPF (Diesel Particulate Filter) or similar component is clogged, preventing the engine from properly expelling exhaust gases and, consequently, not allowing enough fresh air to enter.

I would like to suggest, as Rainer did, that we start with A+B.