Air Mass Meter AJM - Values too high

Hello, tinkerers,

I'm having a problem with the LMM (Engine Control Module) in a Passat 3B with the AJM engine:

The engine starts and runs normally, so far so good.

The thermostat is apparently defective, as the temperature display in the KI remains low, and all sensors (MWB 007 in VCDS) report matching temperatures, but the heating system does not heat up properly. So, I'll be moving soon.

While reviewing the measured values in VCDS, I noticed that the LMM is providing significantly higher values in MWB004:

e.g. in idle mode: Target value: ~250 Actual value: ~500

Previous Attempts:

- No errors in the MSG.

- New LMM installed -> same behavior.

- LMM from another Passat, also AJM, installed -> same behavior. (In the other Passat, these LMM values are correct!)

- The voltages at the LMM are within acceptable limits. How precise do the 5V readings need to be? My multimeter might not be very accurate. It shows 4.95V on this car, and 4.97V on the other Passat.

- LMM Connector Disconnected: Fixed Replacement Value, Error in the MSG.

- Replace LMM with a diode between +5V and the signal. MWB004, the actual value is very high and constant. Same behavior with the other Passat.

- I haven't noticed any holes in the air intake path. Does it need to be audible?

Therefore, I believe that I can rule out a defect in the LMM and wiring. There are also no indications that anyone has attempted to perform cheap modifications.

Next, I'll take a test drive with both cars and log the RPM, boost pressure, and the two mass airflow values.

Could it be related to the thermostat?

Do you have anything else to add?

Thanks for your input!

Martin

1. Possibility
The AGR has been shut down.

2. Possibility
Leaking air intake duct

Hi,
An aging LMM becomes noticeable due to excessively low values. See here.
/viewtopic.php?t=3347
Swapping with another vehicle of the same type is initially not a bad idea, but it probably leads to Option 1 of Matthias.
Why?
A leak on the TL pressure side would be noticeable when the system is under (full) load, not when it's idling.
You can recognize the non-responsive AGR by observing that, under light load, the actual values are too high, and under heavy load, they follow the target values (e.g., during full throttle acceleration). Because in that case, the agricultural sector is already benefiting.
hg
Herbert

90% of the AGR plant closed down

Thank you for your input!

I checked and indeed: the AGR is fitted with a nearly invisible panel at the seal below the AGR valve.

The downside to the explanation is that this seems to be the case for both of the cars I compared. This would mean that the LMMs should behave in the same way, or?

Regarding the Passat that we're actually talking about (the one with the MSG-A), I'm confident that there is a continuous sheet metal structure. Regarding the other one, I still need to carefully check if the AGR is actually completely closed.

To obtain LMM values in operation, I performed a nearly identical test drive with both cars: acceleration from a standstill and logging of RPM, LMM should, LMM is, and boost pressure. The gap in the diagram was caused by my fellow traveler, sorry.

Greetings
Martin

Hello,

Did you actually unscrew the connection pipe, or are you just assuming there's a blocking plate?
The original poem is made of thin V2A steel and cannot be distinguished from a lock without external removal.
Expand and observe makes you smarter

VW Part Number for the seal: 038131547A (check on Google)

Greetings, Mpire

Hello,

yes, there are two seals and a thin sheet of metal in between, which can be seen quite clearly with a magnifying glass.

I have now replaced the thermostat, and the temperatures are now normal. The LMM value remains unchanged and is still high.

Once it's not so cold anymore, I'll remove the AGR panel.

Greetings
Martin