Best LMM Diode Replacement: Optimal Choice

Hello fellow DIY enthusiasts,

'Since my mass airflow sensor (MAF) is also now faulty, I've decided to replace it with a diode. I started with a 1N4148 from my parts bin. A short test drive confirmed that the power is back. Then I measured the voltage drop across the diode and found that it was 0.58V, resulting in 4.39V at the signal input. For comparison, I also tried a 1N4002. With that diode, I got a remarkable 4.42V at the MAF signal input. Question: Up to what voltage value does the engine control unit (ECU) even care about the applied voltage? Are 4.39V sufficient, or do I need to look for a different diode with a lower voltage drop? The second point is that without the MAF sensor, the ABS symbol is displayed on the dashboard. There's also an additional diode on my MAF sensor, connected to two terminals. Is there a connection between these two things?'

Note: Unfortunately, I currently don't have a working laptop, which means I'm also unable to read the LMM values or any error codes myself.

Hello,

What are people's thoughts on the idea of incorporating a small solenoid valve into the crankcase ventilation system, which would only be activated when the ignition is switched on?
'This way, no smoke or mist can reach the mass airflow sensor, which could potentially extend its lifespan. Surely, this would be beneficial for a V6 TDI, right?'
'The ABS symbol is also appearing on my car, and the engine, including the automatic transmission, is going into limp mode.'
On my third attempt, the control unit malfunctioned, and the workshop said it could only go 20 km/h. To fix it, I had to disconnect the battery voltage, and then it worked again.

Best regards, Manuel.

Hi Manuel,

The actual problem with the V6 engine doesn't lie with the catalytic converter, but with the fact that the mass airflow sensor (MAF) continues to receive power for approximately 5 minutes after the ignition is switched off. This time is sufficient for the fumes in the intake manifold to burn and deposit heavily on the MAF sensor. At VW/Audi, there's even a repair instruction for the frequently failing MAF sensor. This involves disconnecting the MAF sensor's power supply and replacing it with the normal ignition power from the engine control unit.

Hello,

That's obvious, but if you prevent both of those things, he might last even longer!
Putting that aside, if we built something as bad as Bosch at work, we would have been fired a long time ago. But with VW, the customer has to take care of getting replacements!

Best regards, Manuel.

Hello,

If you need a diode with a lower voltage drop, Germanium diodes like the 1N60 (price approximately €1.15) should produce a maximum voltage drop of 0.3 volts.

Best regards from Mulag.

Hello,

That's obvious, but if you prevent both of those things, he might last even longer!
Putting that aside, if we built something as bad as Bosch at work, we would have been fired a long time ago. But with VW, the customer has to take care of getting replacements!

Best regards, Manuel


I don't want to criticize, but the application guidelines for the HFM explicitly state:

Do not operate the vehicle during the engine control unit (ECU) initialization process (i.e., the 12V power to the heater must be switched off via terminal 15, not via R-109!).

Do not draw in raw air from the radiator grille or areas where splashes and spray are likely to occur.

The distances to the connection point and the routing of the pipes are predetermined (e.g., the slope from the heat source to the connection point).

In particular, the first two points are often completely disregarded within the VAG group.

CU Gremlin.

Bosch can't be blamed for this. The parts are manufactured according to what VW demands.
Bosch also manufactures parts for Toyota and many, many other car manufacturers. And that works perfectly well.
For me, it's clear that VW is to blame...

Subject: Fuel pump for TDI engines: Bosch prohibits the use of biodiesel. VW allows it, even though Bosch (who presumably know what they're talking about) claims that the seals won't last long under those conditions...

Regards,
Bubu.

Hello Marco,

Did you manage to fix the issue with the diode? I'm interested to know if you were able to get the ABS light to stay off, even when the engine is running without the mass airflow sensor.

Best regards, Manuel.

Hi Manuel,

Unfortunately, I'm only able to provide an answer now because I only managed to continue testing it today.
'In my case, when using a diode as a replacement for the mass airflow sensor (MAF), the error message 'Knock sensor 1 (G61) blabla...' is displayed. If you remove the small temperature sensor from the MAF and connect it appropriately, the error disappears, and a value of 1009 is reported as the air mass. I left the temperature sensor on the MAF, completely disassembled the internal components of the MAF, and then soldered a 1N4148 diode to the internal contact strip of the MAF.'

@all
That was my DIY/test project, not that anyone should complain that I missed the chance to get a new one for 75 euros.

Marco.

'If you remove the small temperature sensor from the mass airflow sensor (MAF) and connect it correctly, the error disappears, and a value of 1009 is reported as the air mass. I left the temperature sensor on the MAF, completely disassembled the internal components of the MAF, and instead soldered a 1N4148 diode to the internal contact strip of the MAF.'


Hello, could you please define that in more detail? I'm also tired of buying new LLMs or exchanging them, so I'd like to try the diode trick.
I have obtained a 1N4148 diode. Unfortunately, I now lack the technical expertise to install it correctly. (For example, in which direction does the diode need to be oriented, which contacts should it be soldered to, and is it absolutely necessary to disassemble the casing and, consequently, destroy the grid?)

Thank you in advance.
René.

Hello fellow enthusiasts,

My questions have been resolved. I found the technical article about the LMM. It describes the diode issue very well...

Regards,
René.