AFN LMM - A different kind of error

Passat99 AFN, 150,000 km.

"The following is a description of the error:"

The vehicle occasionally fails to accelerate properly, or the engine speed drops to idle.
Repeatedly engaging and disengaging the clutch can fix the issue. The vehicle will then run normally for a while.
"That's how the vehicle owner described it."

First, I took a test drive to get a better understanding of it.
The vehicle felt a bit sluggish overall, but I thought it might be due to the added DPF. After driving for a few kilometers, I tried to accelerate, but suddenly the power cut out, it wouldn't accelerate anymore, and then the car slowed down until it came to a standstill. I had to shift gears a few times, and then it started working again.

Fault memory: 00553 - Mass airflow sensor (G70) - 27-10 - Implausible signal - Intermittent.

"Recently, I've noticed that when encountering these error messages in more modern vehicles, the hardware (e.g., a faulty camshaft, missing plugs) is often the culprit rather than the mass airflow sensor (MAF) itself. Therefore, I decided to conduct a test drive."

3rd gear, full throttle, starting at 1200 RPM. Fortunately, the error occurred almost immediately .
The air mass concentration decreased to a value of 190 mg/H.

At the same time, the "throttle position" (not driver demand) also gradually decreased, eventually dropping to 0% after a longer period, causing the vehicle to lose 200 RPM. Admittedly, a significant amount of time passed before this condition occurred.

During the test drive, it all happened within a few seconds.

First, there's a lot of guesswork involved in figuring out why the accelerator pedal sensor is failing – it doesn't quite fit the typical error pattern. I haven't encountered this behavior before. It's very suspicious. What does the accelerator pedal sensor have to do with the air mass?
When two seemingly independent errors occur together, it's usually caused by a third factor, I thought.

Before I completely exhausted myself, I decided to take the path of least resistance and replaced the mass airflow sensor, which is what any apprentice in their first year of training would do.

The ways of the Lord are mysterious. Errors corrected .

What I didn't understand was the relationship between the measured accelerator pedal position and the air mass.

It didn't really take me much time, which makes me a bit thoughtful about software development. Is there an explanation for that?

Hello,

Possibly, the faulty mass airflow sensor (MAF) pulled down the +5V voltage supply of the engine control unit (ECU), which could explain the progressively decreasing throttle position.

Best regards, Rainer.

Okay, that sounds plausible. Unfortunately, the error memory doesn't register any of that.

Although there are very few of these items left, I still find it interesting for future generations to see how certain errors can "manifest" in practice.

Shouldn't the amplifier detect that (a short circuit to ground)?
hg
Herbert.