G70 Error: Troubleshooting and Causes

Hi,

My 1.9 TDI (ASV engine, manufactured in 2000) is acting up again, and I've been experiencing...

G70 - Air mass sensor signal implausible.
Sporadically.



"After being cleared in the diagnostic system (FSP), the error code sometimes reappears after only 10 kilometers. I then researched articles and used the search function, and ultimately replaced the mass airflow sensor (MAF). However, the problem persists unchanged. Now, I've logged a 10-kilometer drive using VAG-COM and have encountered some inconsistencies."

I've noticed that the actual air mass values are significantly different from the target values, sometimes by more than 200 mg per cycle. Interestingly, the engine is receiving more air than it should be – what impact does this have on me?


The EGR valve closing ratio only goes down to 4.8% => shouldn't the EGR completely close under full load? Or am I wrong here?


How would you proceed now? What else could be the problem with the Mass Air Flow Sensor (MAF)? It's a replacement MAF from Pierburg. But it can't possibly be that both the new Pierburg and the original VW (BOSCH) MAF sensors are producing exactly the same errors.



I haven't noticed any significant loss of performance, except for a slightly uneven acceleration at times, which I think is probably due to incorrect airflow.


I've attached the log file here; I've formatted it to be somewhat readable. I can also create a graphic of it if you'd like.

Here: http://gscardesign.kilu.de/Daten/dieselschrauber/log_convert.pdf



It would be great if someone had a possible solution.


Regards,
George.

Sure, here is the translation of the text from German to English:

"Addendum," or "P.S." (postscript) in some contexts.

I found that the car is leaking oil from the hose connection at the cylinder head cover breather, which vents directly into the intake manifold behind the mass airflow sensor (MAF), i.e., between the MAF and the turbocharger. The O-ring was damaged. I replaced it, cleaned everything up, and now I'm waiting to see if it stays sealed. Has anyone had any experience with this causing inaccurate MAF readings?

The volume control cannot go all the way down to zero; otherwise, it wouldn't be a volume control anymore.
When you check the logs, you can see if the "LM is" value has changed.
I think that if unmetered air is being drawn in behind the mass airflow sensor (MAF), it should register as a lower reading than it actually is. Am I wrong about that? I haven't tried it yet.

Quote:

This is a replacement mass airflow sensor (MAF) from Pierburg.

No, it's almost certainly from "Ching-Chong Land" and is a fake.

The problem occurred with both the original Bosch mass airflow sensor and the Pierburg one. The Pierburg unit, by the way, is supposedly from Germany and was ordered directly through our distributor from Pierburg.

Yesterday, I took a replacement Mass Air Flow (MAF) sensor from Bosch at work and installed it – the problem still persists.

It's highly unlikely that the problem is with the mass airflow sensor (MAF) when three independent MAF sensors, two of which are from Bosch, all report the same error.


I'd also like to know where you got the information that my parts distributor is selling me counterfeit products – that's nonsense.

teileklaus wrote:

The volume control doesn't go all the way down to 0; otherwise, it wouldn't be a volume control anymore. When you check the logs, you can see if the "LM is" value has changed. I think that if unmetered air is drawn in behind the mass airflow sensor (MAF), it should measure less air, or am I wrong? I haven't tried it yet.

Possibly, yes. In any case, it always made a strange hissing sound when accelerating at 3000 RPM – which is now significantly better thanks to the new O-ring.

"Yesterday evening, I ordered a new set of hoses and the pressure regulating valve that's responsible for cylinder head ventilation. In my opinion, it's not completely airtight even with a new O-ring."

and it doesn't matter about the 30€ .


You're right about the duty cycle; my mechanic confirmed that to me yesterday as well.

He also thinks the log file is generally okay because it's normal to have a difference between the target and actual values when you accelerate, and then the system needs to adjust. So, I'll do another logging session later with longer distances and constant throttle position to compare the target and actual values again.

Hi,

Ibiza1986 wrote:

The error occurred with both the standard BOSCH mass airflow sensor... and also with the Pierburg one. The latter, according to the printing on it, is from Germany and was ordered directly through our distributor from Pierburg... Yesterday, I took a replacement Mass Air Flow (MAF) sensor from Bosch at work and installed it – the problem still persists. It's highly unlikely that the issue is with the mass airflow sensor (MAF), especially when three independent MAFs, two of which are from Bosch, are all reporting the same error.

Okay, those are arguments, except for the printings on the packages/labels.
The error is certainly typical for low-quality imitations and occurs on software versions that are susceptible to such issues in various engine control units.

Quote:

There's this weird hissing sound at 3000 RPM

. Oh, I see...
Then, the most likely cause for excessively high air mass readings is probably a leak in the charge pressure system, such as a crack in a hose or the intercooler, etc.

Does the exhaust gas recirculation system function correctly, meaning is the difference between the target value and the actual value within +/- 5% at idle with a warm engine?

Best regards, Rainer.

Hello Rainer,

I wasn't trying to attack you or your expertise, but it seems unlikely that three different language models would reproduce the same error.

I'm ruling out a leak in the intercooler system; I've carefully examined all the hoses, and usually you can see oil leaking if there's a problem with a hose. And I haven't experienced any loss of power, so I have 100% top speed, full acceleration, and no hesitation.

I was hoping that the problem with the replaced O-ring on the cylinder head vent had been resolved... but yesterday, when we were reading the diagnostic data at the workshop, we saw the same error code again in the FSP (Engine Control Unit).

The EGR system seems to be working fine so far, especially since I replaced the EGR valve just last winter. At that time, I also replaced all the vacuum hoses because some of them were already starting to become brittle.

According to SEAT, this hissing sound is coming from the turbocharger and is perfectly normal. None of our other TDI models make this noise, but when the head gasket was replaced, the turbocharger was also completely inspected and found to be in perfect working order.

I also have very minimal oil consumption, about 0.1 liters per 15,000 km.

Ibiza1986 wrote:

My 1.9 TDI (ALH, manufactured in 2000) is acting up again, and I'm experiencing the following: G70 - Air mass sensor signal is implausible. Sporadically. If the part is installed in the FSP and then removed, it sometimes reappears after only 10km. I then searched through technical articles and used the search function here and ultimately, I first replaced the mass airflow sensor (MAF). Bitte gib mir den deutschen Text, den du übersetzt haben möchtest. I was hoping that the problem with the replaced O-ring on the cylinder head vent had been resolved... but yesterday, when we were reading the diagnostic data at the workshop, we saw the same error code again in the FSP (Engine Control Unit). AGR is working fine so far, especially since the AGR valve was replaced by me last winter. I also replaced all the vacuum hoses back then, as some were already starting to crumble.

Apparently, you overlooked the FA (fault analyzer) with the error codes for the ALH engine, because it says...

Quote:

Error code: 16485. Air mass sensor G70 - implausible signal. Possible causes: G70 malfunction. Line interruption, short circuit to ground

Try to guess where I would (continue) looking if I were in your place

Quote:

Interestingly, the engine is getting more air than it should - what impact does that have for me?

There are other FAQs here that you might find worth reading, such as the one about creating log files...

Yep.

I missed that. I'm going to cut the entire wiring harness today; it's a really stupid job because the battery and everything else are in the way.

Also, I also wanted to try pulling the pins out of the connector housing and see if there's any corrosion or looseness at the crimped connection point between the pin and the cable; a friend who's a master technician suggested that to me yesterday.

I downloaded the wiring diagram from ELSA yesterday, and I'll take a look at it later.



Regarding the log files: I didn't have time for a graphical analysis . Normally, I do that because we also provide the log files to customers when their cars need repairs. However, I am currently so stressed that I simply couldn't manage it, please excuse me.

Ibiza1986 wrote:

Regarding the log files: I didn't have time for a graphical analysis

. My response was not aimed at that direction, but rather at the significance of the LuMa target values when running at full throttle...

Oh, I see.

Okay, I now understand that the air mass needs a moment to catch up when you accelerate fully. According to my workshop, the log file seems to be fine overall. I'll start disconnecting the wiring harness around 10 AM.

I actually wanted to do it yesterday, but then a family member's car with a leaking transmission came up, and I had to replace the shift shaft oil seal first.

I'm not quite a complete expert on TDI technology yet, but I have a good basic understanding and can usually handle everything myself. However, this forum is really a huge help when it comes to the finer details.

Check the connector on the MAF sensor first before you cut all the wiring harnesses.

Yes.

The connector is completely intact and shows no signs of damage. I also removed all the pins and checked to see if there was any damage at the point where the pin connects to the cable, but everything looks as good as new.

I haven't had the chance yet.

I'm planning to look into this over the weekend. Does anyone have a wiring diagram for the MAF sensor (LMM) from an ALH engine? Before I start disconnecting everything, I think it would be better to run five new cables in parallel and test if that resolves the issue.

I already have connectors for the mass airflow sensor and the connector for the engine control unit in stock.

In my desperation, I've now bought a certified used original Bosch mass airflow sensor and hope that this will perhaps fix the problem.

If it's still not working after that, then it's definitely the cable connection because it's unlikely to have three failures with three mass airflow sensors.

A schematic diagram would still be helpful.