Insufficient supply voltage at N75

Help, my supply voltage at the wastegate valve is only 6 volts. It should be 12 volts!

Now, I would like to know which output pins of the control unit I can check to see if the signal there is also only 6 volts, which, unfortunately, would indicate a defective motor control unit!

Or does anyone else have any ideas about what might be causing it? More tips for narrowing down the source of errors?

My problem is the 'intake manifold pressure control differential' (not sporadic), but it still only happens occasionally! 5 times in about 2,500 km!

AFN engine, manufactured in 1996, installed in an AUDI A4, with Wimmer software. I'm currently excluding the software as a potential cause of the problem!

Thank you.

Manuel.

How did you measure the 6 volts?

Assuming a 50% pulse-width modulated 12 volts, you have (somewhat smoothed) 6 volts }.

And that's exactly what this thing is supposed to do!

You definitely weren't using an oscilloscope, were you? Only when you experience a drop in the peak voltage is there cause for concern.

In addition, the N75 is controlled by the EDC system based on mass. That means it receives both the positive voltage and the pulsed mass.

Okay, let me reiterate:
(1) You should measure between 0 and 12 volts between the connections (a somewhat simplified explanation).
(2) One of the ground connections to the car's mass should have 12 volts.

If any of the points are incorrect, please report it again.

(or correct me

m;

Help, my supply voltage at the wastegate valve is only 6 volts. It should be 12 volts!

Now, I would like to know which output pins of the control unit I can check to see if the signal there is also only 6 volts, which, unfortunately, would indicate a defective motor control unit!



Which voltage do you have at which pin?

You should have 12V on one of the pins of the connector when the ignition is on.
On the other side, you measure whatever your measuring device indicates based on the current duty cycle being applied (the control unit switches the ground). The pin would be T121/62.
The wire colors for Golf/Bora are yellow/black for 12V and red/brown for the control unit. However, wire colors often vary between different brands.

There's only 6V on the power supply side, which indicates a problem with the wiring. A wire from relay 109 goes to multiple fuses. In my diagrams, the N75 valve is connected to the same fuse as other valves and the mass airflow sensor (MAF), but this might be different for Audi.



CU Gremlin.

I'm sorry about the photo, I have no idea what my camera was doing!

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According to my repair manual, there should be 12 volts between pin 1 and ground.
But there are only 6 volts there!

But there are 12 volts between pin 2 and ground!

I'm completely confused right now!

So, everything's okay after all, just a mistake in the repair manual?

Regards,

Manuel.http://www.edv-schreiber.at/audi4ever/fdb/pics/700_57966ba63b86a99ce13e3d361804e681.jpg{MARKER}

Well... it depends now.

If the throttle position sensor reading exceeds 90% with the engine idling, you should be able to measure approximately 12V between the pins.

However, this measurement method is highly dependent on the specific measuring device used.

To be honest, I believe your tuning software is the cause of the problem.

You have a chip and a larger charger for it. I can't imagine that the software takes that into account. Then, overcharging can be quite problematic.
The VNT17 has a different characteristic behavior compared to the VNT15, and this must be taken into account in the parameter fields.
Okay, ich bin bereit. Gib mir den deutschen Text.
I'm using 0.9 bar as a rough guideline at 50% (arbitrary values).
The 17-liter tank is now at 1.1 bar with the current valve setting. By the time the control loop adjusts (and it restarts from the small loader), it will be too late.

Therefore, you should first log the air-fuel ratio. Since you've already mentioned having issues with boost pressure using the larger turbocharger.
Of course, the cause could also be in the boost pressure sensor. Have you checked that already?
Do LDA and VAG-COM displays differ?

CU Gremlin.

During the measurement, the engine was off, and only the ignition was on!


To be honest, I believe your tuning software is the cause of the problem.

You have a chip and a larger charger for it. I can't imagine that the software takes that into account. Then, overcharging can be quite problematic.


That's the strange thing – the 'intake manifold pressure control differential' error doesn't occur due to excessive boost pressure, but rather it happens randomly, without any apparent connection to anything else.


I was just taking a look at the wiring diagrams.

There, I noticed that the ORIGINAL AUDI repair instruction is incorrect! No wonder the workshops are only delivering substandard work.
The PINs are swapped!

I also had another error code in the error memory that I hadn't paid attention to yet: G70 short circuit to ground!

According to the wiring diagram and the actual situation in the car, the supply voltages for components N75 and G70 are connected via a single wire. And if the G70 shorts to ground due to a defect, it will also cut off the power supply to the N75.

Result: Intake manifold pressure regulation differential!

Am I correct in my assumption?

Now, only one question remains: what about the 6 volts on pin 1 (the wire between the N75 and the MSTG)? Are they okay when the engine is off but the ignition is on?

Regards,

Manuel.

Manuel Thomas wrote:

And if the G70 shorts to ground due to a defect, it also takes the supply voltage away from the N75!

Hi Manuel,

The aforementioned 12V supply voltage comes from (the infamous) relay 109, whose load input is "directly" connected to the battery.

If a device like the LMM (G70) is connected to a 12V power supply in a way that creates a short circuit to ground, then immediately several amperes of current will flow, and the component with the (relatively) highest resistance will quickly burn out.
The latter would likely be the practical application of the LLM.

As long as your LMM (likely referring to a Large Language Model) isn't overheating and malfunctioning, you can use the above-mentioned... Scenario can be safely ruled out .

@ ULF,

'But the error message was there, and nothing was actually burned!'

So, it seems my control unit is probably broken. I'm getting 6 volts on pin 1 when the ignition is on, and it should be 0 volts when the engine is not running, which means there shouldn't be any duty cycle applied!

Regards,

Manuel.

From relay 109, the power initially goes to a fuse, and then from that 10A fuse to all the solenoid valves and the mass airflow sensor (MAF). For example, the fuel injector control is also connected to it.

'Short circuit to ground' means that the sensor voltage drops to approximately 0V.
This also happens even when the power supply to the sensor is interrupted.

According to the schematic diagram, the section responsible for the output voltage of the mass flow meter is powered by the EDC (5V). Therefore, the 12V is only used for heating the sensor element.
I'm leaning more towards a faulty mass airflow sensor.

btw: Have you checked the usual suspects? I mean, the VTG (Variable Transmission Gear) and especially the valve itself?

CU Gremlin.

Manuel Thomas wrote:

So, my control unit is probably broken, because I have 6 volts on pin 1, with the ignition on, and it should have 0 volts there when the engine is not running, and therefore there shouldn't actually be any duty cycle!

NO!! (at least not necessarily)

As long as you measure the full battery voltage between any contact of the N72 connector and ground, it almost doesn't matter what you measure on the other pin (it's a clocked voltage!).

As long as the VTG (Variable Turbine Geometry) moves noticeably shortly after the engine starts, this strongly suggests that there is no defect in the engine control unit.

Or, to put it another way:
Connect an analog measuring device in parallel with the connected device. N75.
When the ignition is turned on and the engine is running, only a minimal voltage should be measurable.
After starting, the voltage should rise to approximately 12-13 volts.

Or, to put it another way:
When performing a VAGCOM actuator diagnosis on the N75 valve with the engine off, you should hear the VTG (Variable Turbine Geometry) working quietly, approximately every second (it sounds similar to a ventilator, but without loud breathing noises). Then the hardware of the engine control unit is okay.

OK, SUMMARY!

'VTG tested and confirmed to be functioning correctly, vacuum actuator for VTG adjustment is fully functional, EGR system is operational, air filter is clean, all vacuum lines are in place, engine has full power, and does not produce excessive smoke!'

'Over the last 2,500 km, the error messages 'charge air pressure control differential' and 'G70 short circuit to ground' have appeared 5 times.'

Today, I took the car to the workshop because I didn't have a VAG-COM to read the diagnostic trouble codes. I was particularly interested in the aspect ratio.

1.5 hours later, I was 90€ poorer and was discharged with the information that the engine control unit is defective because the voltages at the N75 valve are not correct! Do not ground!

I took out my multimeter and measured it myself at home.

Connector N75.
PIN 1 to PIN 2 = 6 Volts.

Posted here, and after the first response, I realized that a statement from one of my old mentors has once again proven to be true: He who measures, measures nonsense!

Blushing, she quickly went to the car and apologized.

Connector N75.
PIN 1 to ground: 6 volts (should be 0 volts according to the workshop).
Connect PIN 2 to ground (0V).
Measurement conditions: Engine off, ignition on!

According to my original repair manual, completely different values should be there! According to the 'Jetzt helfe ich mir selbst' (Now I'll help myself) book, there should be 12 volts from pin 2 to ground (ACTUAL). There's nothing specified for pin 1.

Now, my final question: Must the voltage at pin 1 be 0 volts when the ignition is 'on' and the engine is running? Or are my 6 volts also okay?




As long as the VTG (Variable Turbine Geometry) moves noticeably shortly after the engine starts, this strongly suggests that there is no defect in the engine control unit.

When performing a VAGCOM actuator diagnosis on the N75 valve with the engine off, you should hear the VTG (Variable Turbine Geometry) working quietly, approximately every second (it sounds similar to a ventilator, but without loud breathing noises). Then the hardware of the engine control unit is OK.

VTG speed after engine start, maximum. Attention!

Does the VTG rod also move, or am I just imagining it? I'll go back to the mechanic tomorrow to have the N75 actuator diagnosed.

Regards,

Manuel.

Gremlin wrote:

From relay 109, it initially goes to a fuse, and then from that fuse, a 10A fuse, to all the solenoid valves and the mass airflow sensor (MAF).

For example, the fuel injector adjuster is also connected to it...
Hi Ralf,

In my AFN-SLP (Golf 3), between the 12V supply of the MAF sensor / N75 / injector control unit... and Batt+ there is only the load contact of relay 109 (and of course various cables), but no fuse.

Therefore, my story about the fire...

Manuel Thomas wrote:

In the last 2,500 km, the error "intake manifold pressure control differential" and "G70 short circuit to ground" have appeared 5 times.

Hi Manuel,

If the car otherwise behaves in a reasonably normal way (boost pressure + performance), then there is likely no serious defect - because otherwise, you would have constantly a lack of power.

Quote:

Now, my last question is: MUST the voltage on pin 1 be 0 volts when the "ignition is on" and the "engine is running"? Or are my 6 volts also okay?

Here's my answer again:

Quote:

As long as you measure the full battery voltage between any contact of the N72 connector and ground, it almost doesn't matter what you measure on the other pin (toggled voltage!). Bitte gib den Text an, den du übersetzt haben möchtest. Connect an analog measuring device in parallel with the connected device. N75. When the ignition is turned on and the engine is running, only a minimal voltage should be measurable. After starting, the voltage should rise to approximately 12 - 13 volts

.
If the last test yields these results, your engine computer will not have a hardware defect at the N75 output. (what else you measure is irrelevant).
-> Possibly amateurish chip tuning...

Sorry, Ulf.

It probably sounds like I'm not listening to you!

That's not the case; we were just writing our answers at the same time, so I couldn't respond to your statement.

I tried doing that later using a quote!

Regards,

Manuel.

Manuel Thomas wrote:

VTG trips after engine start, maximum. Attention! Does the VTG rod also move, or am I just imagining it? l

Hi Manuel,

So, at least the N75 output on your engine computer is not defective!

The rod moves during the actuator test in the same way as it does after the engine starts.
Just going back and forth.

EDIT:
It doesn't matter whether the 12V is connected to pin 1 or pin 2 on the connector; the solenoid valve will function the same way.
It always reacts the same way, regardless of the direction of the current flow.

In the case of "reverse polarity" of the plug, at most, only people who want to measure the electrical circuit will be confused .

In my AFN-SLP (Golf 3), between the 12V supply of the MAF sensor / N75 / injector control unit... and Batt+ there is only the load contact of relay 109 (and of course various cables), but no fuse.

Therefore, my story about the fire.

Ahhhh, yes...

Then, it's obvious that someone learned from that, because my cited plans are from the Golf 4 .

CU Gremlin.