Golf IV Cabrio (1E) - Exhaust emissions warning light

Hello,
The vehicle is a Volkswagen Golf IV (1E) Cabriolet, manufactured in 2001, with a 2.0-liter gasoline engine producing 115 horsepower.
Mileage: 38,000 km, Engine code: AWG, Transmission code: DFQ.

1. Problem.

The exhaust warning light has been continuously illuminated for some time now. I've already done some research in other forums and through Google searches to find out what could be broken.
First, I read the error codes. It contained the same thing as always.

EVAP Emission Control System: Malfunction.
P0440 - 35-10 - - - Intermittent.

I don't think it's related to that, because the error has been appearing in the error memory since I bought the car (at approximately 31,000 km).
That's all that was stored in the memory. Subsequently, I logged the measurement blocks 001;006;032 while the engine was idling (see attachment).

According to this, the lambda sensor seems to be working correctly, as lambda values are appearing in measurement block 001. However, in measurement block 006, the last value always shows -5.5, and the first two values in block 032 always show 0 (all with the "Lambda" label).

Could the mass airflow sensor be the problem? In other forums, it was mentioned that if nothing appears in the error memory, the mass airflow sensor might be faulty. Angelbich will likely see a faulty oxygen sensor (also known as a lambda sensor) reported in the error log.

What do you think about it? What could be broken, and what does the error code in the fault memory indicate?

Hi,

It shouldn't be a problem with the oxygen sensor and related components.
Look what I found (PDF, external link).
http://lmgtfy.com/?q=inspec40.pdf

Thank you, Rainer, for the nice PDF you posted.


So, it's most likely that the mass airflow sensor (MAF) is broken on the Golf, right?

I don't know if this is related to a faulty mass airflow sensor, but if you...
When I take my foot off the gas pedal, for example, when approaching a traffic light (while still in gear), the car starts to jerk around just below 1400 RPM. It really shouldn't be like that, since the thrust cutoff should remain active until approximately 1000 RPM.
"Furthermore, there's an issue where, sometimes when releasing the accelerator, the values in the fuel consumption display jump significantly upwards (extremely high), even though the thrust cutoff should be active. This error only occurs sporadically, seemingly without any pattern. And as I mentioned, there's also this jerking." It wasn't like that when the car was first purchased.


Okay, and one more thing: In which measurement block can I find the fuel injection quantities?
And what do the values "Mass Flow" (in grams/second) and "load" (in %) represent?

tuner01 wrote:

Thank you, Rainer, for the nice PDF you posted. So, it's most likely that the mass airflow sensor (MAF) is broken on the Golf, right? ... Okay, and one more thing: In which measurement block can I find the fuel injection quantities? And what do the values "Mass Flow" (in grams/second) and "load" (in %) mean?

Air mass sensor? How do you come up with that?

Quote:

The ECM records DTC P0440 or P0442 when evaporative emissions leak from the components within. the dotted line in Fig. 1 below, or when the vapor pressure sensor malfunctions.

The P0440 code indicates a leak in the fuel system. Below in the PDF, you will also find instructions on how the test is performed: it involves checking the vacuum in the fuel/tank system after the drive.

It's possible that the P0440 code appears if you overfill the gas tank and the sun shines directly on the car during a short trip, or if you're stuck in traffic and the car gets extremely hot.
Or, as described in the PDF, a leak can cause uncontrolled air to be drawn into the fuel system/tank.

Mass Flow = mass flow rate, i.e., x grams of air per second (being drawn into the engine).
Load = Load, i.e., how much the engine has to work (idle, full load).

Best regards, Rainer.

I'm bringing up the LMM because I've seen it mentioned in other forums.
The exhaust warning light was on, but the oxygen sensor was still functioning correctly.

But if mass flow represents the amount of air being drawn into the engine per second, then the measurement can only come from the mass airflow sensor, or am I mistaken? (Or are there other things like measuring the intake manifold vacuum?) And if a value is being received, then the mass airflow sensor can't be broken...

I was just looking at some older VAG-COM logs (see attachment).
Maximum flow rate of 88 g/s at approximately 6000 RPM. Isn't that a little bit too little?
And how is the load value determined? In the attached file, you can see that the load value fluctuates to some extent, even though the accelerator was kept fully pressed the entire time.

Hm,

Everything's a bit strange...
The load is primarily determined by the position of the accelerator pedal.

Either there's a rubber mat under the accelerator pedal, the sensor/mechanism that detects the accelerator pedal position is faulty (85% is not full throttle), or the label file is incorrect.

So, your tax identification number is 037 906 018 D, and the VAG-COM distribution and label file are from me?

Possibly, instead of the accelerator pedal position, the throttle valve position is being displayed?

Tell me about your engine, does it have drive-by-wire? How is the throttle valve controlled?

Best regards, Rainer.

Tax device number is correct.

Component: 2.0L R4/2V MOTR HS V02


Under the accelerator pedal, there's a spacer, which seems to have been installed originally. The displayed accelerator pedal position has always puzzled me. I once read that the value should be between 90 and 100 at full load.

I think the throttle valve position is being adjusted, because the accelerator pedal, via a Bowden cable, opens the throttle valve. Some cables also run out from the box where the DK (presumably a device or component) is located.
The idle value is 4.2, and the full load value, as mentioned before, is around 86.

VAG-COM is number 3,112 because I have a self-built optocoupler adapter. I didn't specifically load any label files.

"E-Gas? If it's connected to the accelerator pedal via a Bowden cable, it definitely won't be electronic, or will it? What is referred to as "E-Gas" in gasoline-powered vehicles?" Is the gas position only electronically detected, and is the control valve operated by a servo motor?

How should one proceed? Should we check how far the throttle valve actually opens under full load? If you open it completely, the potentiometer is probably broken.

Doesn't simply opening it shorten the spacer?

Quote:

How should one proceed? Should we check how far the throttle valve actually opens at full load? If you open this completely, the potentiometer is probably broken.

That would also explain the stuttering...

The only question is whether the labeling of the measurement columns is correct... we would need to experiment with the gas and observe what happens and how.

Best regards, Rainer.

The labeling seems correct; you can see that this value changes when the accelerator pedal is pressed, even when the engine is off.

There are new findings:

When the accelerator pedal is fully depressed, the diaphragm valve (DK) opens completely. I initially thought this wouldn't be the case, as the Bowden cable has quite a bit of slack. (When the accelerator pedal is in the idle position, it can still be pulled back about 1.5 cm).

"I noticed something recently: When the accelerator pedal is in the idle position, the value for the throttle body opening in VAG-COM constantly fluctuates between 4.8° and 5.2°."
Quite some time ago, it consistently remained at 4.8°.

According to that, the DK potentiometer is likely broken. Do I absolutely have to replace this, or is there a way to adjust it?

Hi,

If the potentiometer is "jumping" or malfunctioning, it's not worth trying to fix it; it's better to replace it with a new one.
Have you read the article yet?
http://www.ross-tech.com/vag-com/cars/throttlebody.html

Best regards, Rainer.

That would only be relevant to me.

Procedure for performing a throttle body alignment on cars with cable-operated throttles:


I'll try that, but if it doesn't improve things, I'll have to get a new potentiometer.

By the way, the exhaust warning light is off again, just like yesterday.

Hi,

I just finished the "Throttle Body Alignment." The procedure itself worked perfectly. However, even with full throttle, the reading is still only 85.1°. Idle speed is now at 3.9 degrees instead of the previous 4.8 degrees.

However, the value is now fluctuating between 3.9 and 4.2.

I'm going to get a new potentiometer soon.
Could someone please tell me the exact name of this part? Not that the guys at the car dealership don't know what I want from them .

Best regards.

Hi,

If the value is in degrees, that's fine; I thought it represented the accelerator pedal position, with a value somewhere between 0 and 100%.
85 degrees is practically wide open.

The best thing to do is simply write down the VAG part number that's printed on the part, so there won't be any problems at the parts counter.

Best regards, Rainer.

The value is subtitled with:

"T.B. angle" likely refers to "Throttle body angle," hence the specification in degrees.


Is there a way to find out what the target value should be for full throttle? Do they know that at Jung sim Autohaus...?

Here's the translation:

"By the way, are there compatible label files for this engine that work with my older VAG-COM?"
MKB: AWG

85° is quite plausible for full throttle.

What version of VAG-COM are you using?
In the download section, the current label files for the shops have also been integrated into the 409.1 VAG-COM release.

Best regards, Rainer.