LMM or AGR defective? Fabia 1.6 TDI CAYB

After the engine oil change and generator replacement, the following error is stored: [followed by the error description]. Error scan.

Tests for the EGR (Exhaust Gas Recirculation) and MAF (Mass Air Flow) sensors were performed in the basic settings.

AGR Plausibility --> OK.

LMM plausibility check failed -> System error.

After clearing the error, it reappears depending on the engine temperature: cold (after approximately 20 km), warm (after approximately 1 km).

After some trial and error logging while driving, I then obtained readings at a standstill, ranging from idle to full throttle (approximately 2650 RPM).
logged and monitored.

Air mass, target value vs. actual value.
Engine speed, accelerator pedal position.
and deviation of AGR in %.

The situation becomes quite noticeable starting from line 121, where the air mass suddenly jumps to over 500 and then drops again. In line 120, which is 2/10 of a second before, a deviation of -37% is detectable in the EGR (Exhaust Gas Recirculation) system.

Has anyone ever experienced a similar error? I'm a bit unsure whether the mass airflow sensor (MAF) or the EGR valve is malfunctioning.

If it were more accessible, I would have temporarily blocked the AGR valve and re-measured the lambda values.

PS: Assumption -> The error was partially already present..., because according to the information, the glow plug filament has occasionally flickered, but the MIL (Malfunction Indicator Lamp) was off. Now, he is also occasionally turning on the MIL. Unfortunately, I didn't read it beforehand.

Just a thought... Could it be that the learning values were still able to compensate for the error, but that this is no longer the case after disconnecting the battery? ... It's just a thought, because I'm definitely not being careless (e.g. (Wires were pulled).

Hi,

According to KOBD2Check, the current software version for your engine control unit is: 9979.
Unfortunately, there is no information about what exactly was fixed.

So far, I haven't had a single "jumping" LMM (lambda sensor), but I've had several defective EGR valves or throttle bodies.
It's not entirely clear what aspects of the environmental conditions reported in the LMM error message seem implausible, but it might be possible to check the motor control unit's data set to see what values are expected.

Quote:

Exhaust gas recirculation valve: Actual value - ANG_EGRV[0]: 0.000 %

Okay, so either fully on or fully off, in both cases the actual LMM value would be unsuitable if you consider the other boundary conditions of the error.

I would start by checking the wiring and connectors of the mass airflow sensor (MAF) and updating the software of the engine control unit (ECU).
If the problem still persists, I would then look into the EGR valve and throttle body, which, in my opinion, are not as well-designed or easy to maintain on this engine as they are on my BRE.

Best regards, Rainer.

Quote:

I would start by checking the wiring and connectors of the mass airflow sensor (MAF) and updating the software of the engine control unit (ECU). If the problem still persists, I would then investigate the EGR valve/throttle body

.

I'm also leaning more towards AGR. My supplier is providing me with a mass flow meter (MFM). I'll test it out first during the weekend because I have less work then, and if it doesn't work, I can rule it out.

If that doesn't help, I will temporarily block the front AGR (Abgasrückführung) line, as the AGR system itself is also showing fluctuating values.

So far, I haven't been able to identify any issues with the wiring.

Regarding the environmental conditions reported by the error memory, well... can you always trust them when not even a plausible date is provided, or sensor values (e.g.,)? Are we supposed to believe that these are genuine Audi parts, even though they don't actually exist?

I will only send the device to Scoda for an update once I'm certain that I haven't made any mistakes or oversights during the repair process, or if I need to have Scoda handle the update themselves.

Hi.

Quote:

Can we always trust them, when not even a plausible date is given, or sensor values (e.g. Are

Audi models being advertised that simply do not exist in reality?
Good question... Regarding the date, I wouldn't consider it a reliable indicator for my vehicles; so far, the mileage and other relevant parameters have always seemed plausible.

Best regards, Rainer.

If you close the AGR valve, it will likely only work in a low load (LL) situation. However, as soon as you start driving, an error will be triggered, and the system will go into limp mode. That's at least my experience.

I would say it's probably due to the EGR valve.

But if I remember correctly, there's a technical information bulletin (TPI) for this issue that describes how to replace the contacts on the mass airflow sensor (MAF) connector with gold-plated contacts.

Please also measure the target/actual values for the boost pressure and the target/actual values for the EGR.
Here, in post #15, you can see what I mean.
I am unable to access external URLs, so I cannot translate the text from the provided link. Please provide the text you would like me to translate.
The entire process was conducted under constant load and with full-throttle acceleration.
Perhaps you'll see more with it.
hg
Herbert.

Quote:

If you close the EGR valve, it will likely only work in the low load range. As soon as you start driving, an error will be set and it will go into limp mode. These are at least my experiences.

I think so too. The good thing about it is that the error can be reproduced when the vehicle is stationary and the accelerator is fully pressed. It then runs at a constant speed of approximately 2800 RPM.

It would be unfortunate if the system automatically assigns a replacement value to the mass airflow sensor (MAF) as soon as it enters limp mode.

Ideally, the LMM (removed) should be powered by a constant, controllable airflow and then evaluated using VCDS or an oscilloscope to completely exclude environmental factors such as EGR.

I have acquired an LLM for testing purposes. Now, all that's missing is the vehicle.

Quote:

Also, please also measure the target/actual values for the boost pressure and the target/actual values for the EGR.

Yes, I may do that later... For now, I've decided not to proceed because of the sampling rate.