Engine Control Unit (ECU) - Mass Air Flow Sensor

and specifically, the following thing caught my attention today - while experimenting with a diode at 1 mm ...

...that the mass measured in the sensor string is not actually the vehicle mass - I'm getting 0.65V, which indicates it's not related to the vehicle mass.
'Also, the supply voltage for the mass airflow sensor is not 5V, but 5.65V, which, for me, indicates a potential shift for the entire engine control unit. This means that the engine control unit does not have a proper ground connection (because the internal potential that the ECU outputs does not match).'

Okay, here's the translation:

'Now the question is: Is the mass within the sensor chain of the MSG directly connected to the vehicle's ground connection in the water tank? If so, would that mean the vehicle's ground potential is present there, or is there no potential? Or is that not the case?'
or should that be normal, and I don't need to start looking for contact problems?

Devilseye503 wrote:

Now the question - is the mass within the sensor chain of the MSG directly connected to the vehicle mass in the water tank? -> consequence: would it have vehicle mass - meaning no potential difference, or is that not the case?

Okay, so far, on the expanded MSG (Multi-Socket Group), I've measured 0 ohms between the pins for the sensor ground and the vehicle ground.

If the main data stream in the MSG were interrupted, it would likely result in confusing error symptoms (there have been similar cases before -> search).
Therefore, I suspect there's a short circuit occurring between the "main power pin" of the MSG (Main System Generator) and the car body.

The sensor mass is filtered out relative to the power mass.
The voltage shift can occur if 'correct' currents are flowing.
can definitely occur.

Best regards,
Rudi

The sensor mass is filtered out compared to the power mass.
The voltage shift can occur if 'correct' currents are flowing.
can definitely occur.

Best regards, Rudi
Would you classify 'engine off, ignition on' as an operating state suitable for establishing 'correct' current levels? (The engine is warm.)

Yes, that could .
The MSTG itself draws approximately 300mA.
Depending on the engine, different actuators are controlled.
That can add up to quite a few amperes.

Best regards,
Rudi

The sensor mass is filtered out compared to the power mass.


Hello Rudi,
What do you understand by 'filtered'? The sensor mass is surely built discretely within the control unit and has no connection to the power supply ground.

That's also why there's a mass shift between the sensor's ground and the vehicle's ground.

Best regards, Jochen.

Then you would have to have a DC/DC converter installed... Much too expensive .
Furthermore, if there were absolutely no connection between them, you wouldn't measure anything either.

You have DC/DC converters in the MSG, right?
5V sensor supply, +/-15V for the ICs.

Our prototype MSGs have a completely separate analog mass, but it's not a production model yet.

Develsey's measurements clearly demonstrate this separation between the sensor ground and the power supply ground.
(@ Develseye, I also tap into the analog signals with a single-ended connection and measure them against the vehicle's ground. I have the same ground offset issue.)

I'm just wondering why Ulf is measuring 0 ohms and how you understand this filtering when the grounds aren't separated.
Or is it perhaps like this:
The sensor ground is discrete. The RF grounding of the sensor ground is connected to the power ground. This means the potentials are not completely isolated.

Best regards, Jochen.

A DC-to-DC converter is, for me, a component that transforms a direct current voltage A into...
Direct current (DC) creates (or creates multiple) potentials that are not...
Establish a connection.

5V is supplied via linear regulators (some of which are integrated into the PowerASICs).
+-15V... I haven't found that in a motor controller yet; I've...
but I haven't disassembled any piezo elements yet.

Okay, I just opened up an MSA15-7... connecting the power ground to the digital section.
and the analog mass of the C166 - 0.8R, which I measured using - even good - multimeters.
(e.g., Fluke 8060A) – when it comes to the absolute value, I don't trust devices in this price range.

The analog mass is kept separate (as a separate network), but is connected to...
Point - located near the processor or ADC - connected to the digital ground.
A coil can be used as a filter element, for example.

Best regards,
Rudi

Rudi wrote:

The analog mass is kept separate (as a separate network), but is connected to a... Point - located near the processor or ADC - connected to the digital ground. As a filter element, for example, an inductor can be used.

Aha, slowly, some light is coming in.

The current from the sensors flows through the aforementioned (example) coil, and this current raises the potential of the analog ground by an amount equal to the voltage U = R(coil) * I(all sensors), across the digital/power ground.

AFAIK, the aluminum housing of the MSG (at least in my EDC15P) is directly connected to the power ground.
-> When you measure the voltage difference between the housing and the vehicle's chassis, you obtain a measure of the wire resistance between those two points.

This voltage is likely to be around 0.65V even with the engine idling. When the engine is running (and the currents from the PDE and solenoid valves are still being discharged to ground), it is probably several volts higher, which indicates a short circuit!
"Specifically, the current flowing through the LD solenoid valve is not reaching its normal values. This results in a lower vacuum pressure in the charge air control valve chamber, which may prevent the VTG (Variable Turbine Geometry) from fully closing in low load conditions (at a throttle valve opening of 20%), and instead, it only closes fully at the base setting and with a throttle valve opening of 0%."

I suspect the problem lies buried there, which we were trying to fix with a shortening of the VTG rod at first glance...

I suspect that's where the problem lies, which we initially tried to fix with a shortening of the VTG rod...


ulf, you are good - you think along - that's where I wanted to be.
'But shouldn't it be the other way around? Shouldn't there be more vacuum? Because the potential is being pushed upwards, but the N75 valve operates using switched ground. It's recognized as 0% instead of 20% TV, because without any control signal, the N75 valve defaults to full vacuum... it should actually be better in the low RPM range. The problem is that it can't open as quickly, which means it produces overshoot.'
my idea -> double error: VTG too long, insufficient mass -> overshooting (both would be my problem).

@ Ulf
Almost .
Just to clarify, the digital ground (DGND) and analog ground (AGND) should be connected together, and both...
are 'separated' from the power-ground (AGND, which may still be used as a separate network).
in the layout, it is treated like a signal, while DGND is usually implemented as a plane.

@ All
Mass shifts in vehicles are normal - don't worry about them.

If we have two identical cars (without any faults), using the same measuring instruments (!),
'Significantly different values can be obtained (always make sure the measuring tips are...'
If you have the right connections (or can make the right contacts), then you could explore that avenue - otherwise...
I would leave it.

Sometimes it's helpful to connect a 10k resistor to the measurement probes of a multimeter.
to bridge (i.e., connect in parallel with the input of the multimeter); in this case, at least a...
A current of approximately 1 to 1.5 mA is flowing, and no significant charges are being detected.

Best regards,
Rudi

Devilseye503 wrote:

but shouldn't it be the other way around? -> more vacuum?, since the potential is being pushed upwards, but the N75 operates with switched ground.

Where should the N75 get more power or voltage from?

The Plus terminal still has a voltage of 14V relative to the vehicle ground, but its ground pin can no longer be pulled down to 0V relative to the vehicle ground during the PWM phases; for example, it stops at 4V.

Result: The maximum clamping voltage across N75 is 14V - 4V = 10V, instead of 14V. This means the valve opens less, resulting in lower vacuum.

... Simplified example without inductive effects, meaning that even though the terminal voltage might be 14V initially with zero current, the principle still applies.

Result: Maximum clamping voltage across N75 = 14 V - 4 V = 10 Volts instead of 14 Volts -> the valve opens less .
It fits up to here.
-> lower negative pressure
that's where the fallacy lies .
Then, if you were to disconnect the electrical connection, there wouldn't be any vacuum at the outlet anymore - but that's not the case.
In simple terms, the valve fully allows the vacuum to pass in its resting state. When activated, atmospheric air is mixed in, which reduces the vacuum (the valve opens).

Devilseye503 wrote:

that's where the fallacy lies . Then, if you were to disconnect the electrical connection, there wouldn't be any vacuum at the outlet anymore - but that's not the case. In plain English - the valve fully passes the vacuum in its resting position. When activated, atmospheric air is added, which reduces the vacuum (the valve opens)

.
So, that would mean that when the plug of the LD-quantity valve is disconnected, the VTG (Variable Transmission Geometry) is constantly at the closed position?

The consequence would be that, depending on the engine speed, the LD (likely referring to a turbocharger or similar component) would "uncontrollably" increase boost until the emergency mode kicks in! Your engine is the first TDI I've seen that behaves this way, meaning the LD isn't inherently safe. What kind of car is your ARL engine installed in?

The rule I'm familiar with is "no LD valve current means no boost pressure."
Could it be that the hoses for the pressure and vacuum sides are connected incorrectly on the LD valve in your engine? That would explain the observation you mentioned earlier.

So, now we're facing a fundamental question, and I actually thought that this was the case for all the newer TDI models.
Because the name N75 isn't given without reason; it refers to a valve for charge pressure limiting.

which vehicle is around the ARL? I already wrote that last time - Leon .
If my statement is incorrect, then I must have already had several ASV motors that were incorrectly wired at the factory - I also have a function-specific 1J0 906 627 A part right in front of me, which behaves exactly the same way.

'No voltage -> full vacuum at the OUT (output) - coil at 12V (TV 100%) - no more vacuum at the OUT.'

edit, I'm not really understanding this valve right now - without control, there's vacuum at the output - with control, there's vacuum at the output - when the voltage is turned off, there's a brief period with no vacuum at the output - so, I'm not going to say anything else right now - I need a coffee