Installed an extra cable to protect the mass airflow sensor?

I went to the dealer to have the mass airflow sensor (MAF sensor) replaced on a V6 engine with 150 horsepower.
In this case, they removed an additional cable from the mass airflow sensor.
This is supposedly intended to protect the LMM.
Does anyone know what this does?

John.

Please provide more details. Was a connector installed? Was only an additional wire run, and if so, where? Was was this a pre-made part, or was it manufactured by the workshop itself?
If there was no intermediary device, how was the additional line connected?

Hi!

The cable runs from the power supply connection to the fuse box, where it is connected to a fuse that only carries voltage when the ignition is on.

This is done because the original power supply to the mass airflow sensor (the heater!) continues to provide voltage for a relatively long time even after the ignition is turned off.

In order to bypass this reheating process, an additional cable must be installed.

Sure, here's the translation:

'Hope it helps.'

Stefan.

Okay, thanks Stefan.

Stefan . wrote:

This is done because the original power supply of the MAF sensor (the heater!) continues to be supplied with voltage for a relatively long time, even after the ignition has been turned off. In order to bypass this reheating process, an extra cable must be installed.

Hi Stefan,

In principle, that's correct, but:

I know how long the EDC (and therefore the LMM) continues to receive power after the ignition is switched off - incidentally, via the infamous relay 109.

I didn't stop it , but it's about 3 seconds on the AFN.
So, it takes less time than a full preheating cycle (okay, the battery voltage is lower during that, but the heating current is, as far as I know, regulated by temperature).

Even if the mass airflow sensor (MAF) is no longer cooled by incoming air after the engine stops (approximately 2 seconds later), I don't think this is a major problem.

So.

Of course, I can't guarantee it 100%, but my (quite trustworthy) master explained it to me like this.

The now-eliminated preheating time was intended to extend the lifespan of the mass flow meter.

I have a V6 TDi (AFB) engine, and the connector for the second sensor of the mass airflow sensor (MAF), which is for the heater, has been rewired. It's now connected to a fuse in the fuse box that only provides power when the ignition is on.
(I'm not sure exactly which fuse it is right now, but I can find out if needed.)

HOWEVER: When I look at the wiring diagram for my vehicle, specifically for the AFB engine, this particular connection 2 goes directly to terminal 15 of the control unit (ZE) via fuse 5.
In addition, relay 3 (relay for the diesel direct injection system) connects the same terminal again to terminal 30.

It certainly looks peculiar when you examine the circuit diagram.

Hmph....

Stefan.

Here is the internal information from the Friendly team , so the problem and the solution have been known for a while (see the last lines).

AKN/AFB engine, TDI V6.
Gradual decrease in engine power over time and mileage.
No errors found in the engine control unit.
Please provide the German text you would like me to translate into English.
Cause: Oil mist can gradually accumulate on the sensor membrane when the engine is stationary.
to reach, to arrive, to get through, to succeed. The air mass meter signal is increasingly distorted until...
due to a noticeable loss of performance. Through slow changes, mostly...
Sure, here's the translation:

"No error entry."
! Series: Disabling the warm-up phase of the air mass sensor.
! From €11.99, Part No. 4B YN 057 350.
KD: Check the mass airflow sensor. Target and actual values of the intake air.
mass in measurement block 10 analog, repair guide, under load.
compare.
Replace the mass airflow sensor if the target values are not being reached.
ET only supplies parts that are the latest version. Air filter element replacement.
check.
! In addition, measures are in place to prevent repeated contamination of the air mass sensor.
! Perform the following action. (Only applies to vehicles registered under the above registration number.)
! 1. Disconnect the wire from PIN 2 of the mass airflow sensor.
Cut and isolate. The pin numbering is located on the connector.
! 2. New cable (cross-section 1 sq mm) with 2.8 mm gold contact and single...
! zeldrahtabdichtung from pin 2 of the mass airflow sensor to the central...
! Pull fuse 31 (output). Cables also in ISO.
Pull the iron pipe. Connect the cable in the same way as the motor cable.
! Climb the tree, then go through the water tank and the electrical box.
! 3. Verification of the implemented change.
! - Connect the voltmeter to PIN 2 (new cable) and PIN 3 (ground) of the air...
! Connect the measuring device.
! - Starting the engine: The voltmeter must display the battery voltage (approximately 12-14 volts).
! display the voltage.
! - Turn off the ignition. The voltage must be reduced immediately after the motor stops.
! dropped to 0 volts.
! Sure, here's the translation:

"Note:"
! For vehicles prior to the above reference number, the mass airflow sensor is still...
! Remains powered for approximately 4 minutes after the engine is turned off.
! During this "preheating" phase of 4 minutes, the previously mentioned...
"Oil residue is baking onto the air filter membrane." With the new...
"A loose cable can cause the mass airflow sensor to fail immediately after the engine is turned off."
! Ignition disabled.
First edition: 08/18/99/ma
last modified: 10/10/01/ma

hugo wrote:

! During this "preheating" phase of 4 minutes, the previously mentioned... "Oil residue is baking onto the air filter membrane." With the new... "A loose cable can cause the mass airflow sensor to fail immediately after the engine is turned off." ! Ignition disabled. First edition: 08/18/99/ma last modified: 10.10.01/ma

Hi Hugo,

interesting: I thought the preheating phase was a characteristic of hot-wire mass flow meters, but there, it's for the freeburning of the measuring device.

It's beyond me why a preheated hot-wire LMM should be reheated... but it's probably a design flaw anyway (perhaps the electrical circuit designer made a mistake when switching from a hot-wire to a hot-film device? ).
because apparently it also works without reheating, and in fact, it's even better that way!

What surprises me in this context is that I had to get three new LMMs (in 2001, then January and May 2002) before the mechanics at the workshop figured out the problem.

But maybe this is a valuable tip for those who no longer have any warranty or grace period and want to use their expensive item for a little longer...

What's the truth about the rumor that Audi/VW are now supposedly installing mass airflow sensors (MAF sensors) in metal pipes? So, not the plastic casing anymore, but aluminum or something similar?

Stefan.

Hi,
Unfortunately, the 4-minute thing is true. It's just as ridiculous as the workaround, and I thought something like that could be fixed with a software update. Well, I'll have to do it on my car too, if there's no other option. And that's despite the fact that it was supposedly regularly serviced at VAG – if that's actually true – because it should have been due for that maintenance a long time ago.

Does anyone happen to know exactly how to connect to fuse 31? The space available for a typical push-fit connector is extremely limited.