Boost pressure on A3 1.9 PD ASZ engine, electrical problem with sensor

hi,

I managed to get an electronic boost pressure gauge from VDO, but I'm now having a few problems connecting it. The gauge looks like this, and I've labeled all the connectors on the back:

[img][/img]

I've already called VDO, Bosch, and Audi (and also visited several dealerships and workshops) to inquire about the measurement range, etc., of the turbocharger pressure sensor installed in my car. But honestly, no one knew anything about it, not even Bosch, even when I provided them with the part number on the turbocharger pressure sensor! So, I've already tried everything in that regard!

I don't really have much left to do other than trying things out, but I wanted to get some more information from this community first!

Okay, this is where I am so far:

The sensor on the intercooler has 4 cable input/output connections.
Pin 1: Ground (0 V)
Pin 2: NTC charge air temperature sensor connection from the control unit.
Pin 3 provides +5V power supply for the boost pressure sensor.
Pin 4: Output signal (voltage) - Turbocharger pressure sensor.

Since the donor has labeled the input as "G", it's reasonable to assume that the donor's output signal needs to be connected to pin 4. The question is whether connecting the cable from the sensor to the display might distort the values or something similar.

The "+" and "-" terminals connect to a 12V and a GND from the dashboard, but I'm not entirely sure if that will work with the sensor signal. The other two terminals on the back of the display, which I've labeled with "?", are possibly for the illumination, so those terminals would need to be connected to the interior lighting. However, I can't be 100% certain about that, as I haven't tried it yet because I didn't want to risk damaging anything.


I really hope someone has an idea; I've been searching for a solution for ages, but I haven't been able to find anything in the articles I've read! While the article about building a digital boost gauge has some information, I already have a VDO gauge with the correct input, etc.! The question is whether anything needs to be adjusted for ambient pressure, etc.

Thank you in advance.

Best regards.

Jens.http://www.eartouch.com/vdo_lda_2bar.bmp{MARKER}

Hi,

The sensor signal will not be distorted as long as the current remains within the specified range. I can't tell you exactly how much current the display's control input draws, but typically, the FET inputs have negligible current draw.

I can't tell you about the offset either. As long as the advertisement doesn't have a setting option, I only see two possibilities.
A) The display is preset to a fixed value (possibly with an internal sensor for compensation).
B) Upon ignition, the display reads the reference value applied to the absolute pressure sensor and stores this value as an offset.

However, I'm concerned about the instrument's characteristic curve; depending on the boost pressure sensor installed (measurement range), the display should show different values. If the part is new, there should be a connection diagram included with it.

hi,

I cannot tell you what kind of power supply the display requires. Are you asking if it's okay if the device only draws a small amount of power?

What are FET inputs? "But usually, the FET inputs have irrelevant currents."

"I cannot understand this sentence: 'Upon ignition, the display takes the applied reference value for absolute pressure from the sensor and stores this as an offset.'" ... It seems like some words are missing, or I don't understand what it's referring to! I'm not sure exactly what "ignition" refers to, and what is this "offset"?

Oh yeah,... and there's also no wiring diagram available! I only have this ad, nothing else!

Perhaps you were suggesting that the display might be defining the first measured value as 0 bar, or as atmospheric pressure, and that this is affecting the measurement range or display range? I can't interpret it any other way... sorry!

Are you trying to say that it can be safely integrated and connected to the output signal from the pressure sensor, but you're just not sure if the displayed values are accurate? Or what does this generally mean now???

Best regards.

Jens.

Crackbot wrote:

I have already called VDO, Bosch, and Audi (and I have also visited several car dealerships and workshops) and asked them what the measurement range, etc., of the turbocharger pressure sensor installed in my car is! But really, no one knew anything about it, not even Bosch, even when I wanted to give them the number on the turbocharger pressure sensor! So, I've already tried everything in that regard! I don't really have much left to do now except try things out, but I wanted to try to get some reassurance about this community first!

Hi,

The AS sensors I am familiar with have a sensor that measures up to 3 bar of absolute pressure.
Since the sensors are powered by 5V from the MSG, a pressure of approximately 3 bar should correspond to a voltage of about 4.7V.

If your electric LDA is designed to work with an external sensor that requires a 12V power supply (which I assume it is), you will most likely get incorrect readings using the EDC sensor signal.

It's just annoying when you can get something exotic in the store for a cheap price, but without any description .

ulf wrote:

It's just unfortunate when you can get something exotic in the store at a cheap price, but without any description

.

And if that were the case, you would either have to build an adapter circuit yourself (not just a resistor divider, but at least an operational amplifier), or buy the appropriate sensor. If it's for a specific MAP sensor, the price of the display is only part of the cost.

Crackbot wrote:

Are you trying to say that it can be safely integrated and connected to the output signal from the pressure sensor, but you're just not sure if the displayed values are accurate? Or what does this generally mean now???

Okay, to put it simply, when I mentioned "offset," I was referring to the value used for absolute pressure. "FET inputs are commonly found in op-amps, and most 10-cent op-amps now have them. These devices have virtually no current flow because they operate statically or capacitively."

If that thing, as Ulf described, really needs a special intake manifold pressure sensor, then as someone who isn't an electronics expert, I would simply ignore my thread, sorry. Those things are really not made for that.

If the advertisement is for an original sensor, it should clearly specify which sensor it is. It should also be capable of being calibrated or adjusted, as indicated in the user manual.

ulf wrote:

Crackbot wrote: I have already called VDO, Bosch, and Audi (and I have also visited several dealerships and workshops) to inquire about the measurement range, etc., of the turbocharger pressure sensor installed in my car! But really, no one knew anything about it, not even Bosch, even when I tried to give them the number on the turbocharger pressure sensor! So, I've already tried everything in that regard! I don't really have much left to do now except try things out, but I wanted to try to get some reassurance about this community first! Hi, The AS sensors I am familiar with have a sensor that measures up to 3 bar of absolute pressure. Since the sensors are powered by 5V from the MSG, a pressure of approximately 3 bar should correspond to a voltage of about 4.7V. If your electric LDA is designed to work with an external sensor that requires a 12V power supply (which I assume it is), you will most likely get incorrect readings using the EDC sensor signal. It's just unfortunate when you can get something exotic in the store at a cheap price, but without any description

.


If a 3-bar sensor is installed in the ASZ, can a VDO LDA (Linear Density Analyzer) that is rated up to 3 bar be used?

"I suppose I could still find a replacement for that..., I just bought this boost gauge cheaply, and the measurement range seemed appropriate for the ASZ engine." As far as I know, it builds up to 1.35 bar, so a significant portion of the gauge would be used (0-2 bar), unlike the cheaper ones that go down to -1 bar, etc. (In retrospect, a cheaper gauge would have been easier to install).

Well,... what would you recommend now? Should I just install it? Or should I stay away from it? Try something different .

Crackbot wrote:

Well,... what would you recommend now? Should I just install it? Or should I stay away from it? Try something different

.

Hi,

If no values can be found, I would do the following.

Power up the device and, if you have a small laboratory power supply, vary the voltage and note a few values, for example, 0 bar and 1 bar (along with the corresponding voltage). Then, compare these values with the readings from the original MAP sensor. At the same time, measure the current. Values below 5mA are not critical, but can lead to misdiagnoses in cases such as a broken original cable, as the original sensor uses a pull-up resistor (10k ohms) to diagnose contact problems.

If you don't have such a power supply, you can use a simple multimeter to measure the current flowing into the instrument's input relative to ground. Also, measure the voltage at the input and ensure it's 5V. This will help you ensure that you don't cause any damage when you temporarily connect the sensor for testing.

(..) because the original sensor is diagnosed with a pull-up resistor in case of contact problems (10k ohm).

Where did you get that ?

Okay, so my MAP sensor is an active sensor and operates without a pull-up resistor. I can measure the voltage directly. When using a parallel tap, I didn't need to use a pull-up resistor in the measurement system; I simply connected the signal to the Analog_In pin.

A broken cable or short circuit is detected by the absence of voltage or the maximum sensor supply voltage at the analog input. For this reason, not the full 5V of the sensor signal is utilized, see. Ulfs answer.

I don't know how the French are trying to measure the LD (likely referring to a specific measurement or parameter), but using a pull-up or pull-down method is quite unusual.
Even if I were to use a simple, passive voltage divider to measure the LD (light detector output), I would have to account for a pull-up resistor. In this case, the pull-up resistor does not serve for error detection, but is instead the fixed resistor in the voltage divider formed by the instrument and the sensor.

In this case, the sensor is not active and is not powered separately. (2-pole). Sensor)

So, here's where you need to be careful and first understand how the sensor that's being connected works.

If you don't have such a power supply, you can measure the input of the instrument against ground using a simple multimeter (current).

What do you want to measure with that? You are creating a short circuit.
A voltage measurement at the signal input already indicates which type of sensor the measuring device expects.

- When measuring a voltage, it is measured against a pull-up resistor, and a passive sensor is expected.
- If no measurement is taken, an active sensor is expected, which provides an analog output voltage.

@Crackbot

I don't think this instrument is suitable for connecting the series sensor.
Instead, I would look for an LD sensor from VDO that operates on the principle of a voltage divider. At VDO, oil temperature, oil pressure, and other parameters are also measured using passive sensors.

Best regards, Jochen.

Jochen_145 wrote:

Okay, so my MAP sensor is an active sensor and operates without a pull-up resistor. I can measure the voltage directly. When using a parallel tap, I didn't need to use a pull-up resistor in the measurement system; I simply connected the signal to the Analog_In pin. What do you want to measure with that? You are creating a short circuit. A voltage measurement at the signal input already indicates which type of sensor the measuring device expects. - When measuring a voltage, it is measured against a pull-up resistor, and a passive sensor is expected. - If no measurement is taken, an active sensor is expected, which provides an analog output voltage.

Hi,

"Of course, I'm assuming the presence of an active sensor. When I mentioned 'resistance,' I was referring to its use in diagnostics. You know yourself how the MSGR diagnoses signal interruptions." If the connector is disconnected from the LD (Load Disconnect), a 12V voltage is present at the MSGR (Main System Gate Relay) input (via a pull-up resistor in the MSGR). This allows for the diagnosis of three potential issues: a wiring break, a short circuit to the supply voltage, or a short circuit to ground.

You should definitely not create a short circuit to ground, as the display also uses the input as an input. Depending on the measuring device, you will only measure a small voltage via the leakage current of the instrument's input stage. I need to measure the leakage currents, possibly those caused by the pull-up resistor in the display.
Even if the instrument expects a passive sensor, a voltage needs to be applied via a pull-up resistor, because passive components generally don't generate voltage, with the exception of lambda sensors. Are there any passive load cells used in the automotive sector? They typically use a simple strain gauge, which, like a scale, changes the internal resistance based on the strain. A pull-up resistor is absolutely necessary in this case. In short, the sensor and the measuring resistor form an electronic Wheatstone bridge, and this voltage shift is the signal that comes from an active sensor after being amplified by a current amplifier.
In both cases, it is implausible why the instrument would allow full current to pass through to its input.

Of course, I assume an active sensor is present. When I mentioned 'resistance,' I was also referring to diagnostics, as you know how the MSGR diagnoses signal interruptions. If the connector is disconnected from the LD (Load Disconnect), a 12V voltage is present at the MSGR (Main System Gate Relay) input (via a pull-up resistor in the MSGR). This allows for the diagnosis of three potential issues: a wiring break, a short circuit to the supply voltage, or a short circuit to ground.


No, that's not how it's done.
An analog input does not have a pull-up resistor at the input. How else would you measure the input voltage? You would detect the voltage as being inverted.
The software and the sensor characteristics don't indicate an inverted signal.

The diagnosis is made without a pull-up test.
- No signal voltage -> Cable break / Short circuit to ground.
- Sensor supply voltage at the analog input -> Short circuit after power-up.

Therefore, the full sensor supply voltage is not used as the sensor signal.

You definitely should not create a short circuit to ground, as the display also uses the input as an input.
For accurate current measurement, the internal resistance of the measuring device should be as low as possible.
Therefore, you are short-circuiting the input when measuring current against ground.

Even if the instrument expects a passive sensor, a voltage is applied via a pull-up resistor.

Only when a passive sensor is connected. Therefore, do not connect any pull-up resistors to an analog input pin (IDR).
Are there any passive LD systems at all in the automotive sector?
I'm not familiar with any such feature at OEM, but I could imagine that the French might use one. Otherwise, I can't imagine how you came up with the idea that the analog inputs in the MSG are equipped with pull-up resistors. You usually only find this feature in digital inputs, if at all.
'With simple accessory instruments, I'm already familiar with these passive sensors. For example, oil pressure and oil temperature are measured using them.' VDO was captured in this way.

Looking at the image of the VDO instrument, I would say that it is based on the principle of a standard analog multimeter. In short, a resistor connected to pin "G" is needed to ground it, and the indicator will then show a reading.

If that is the case, I would assume that the device will only work with a compatible VDO LDG unit.

A VDO part number should be embedded somewhere on the device (all around). Please post it, and maybe I can find something out.

And by the way, the two connections that you identified as lighting are indeed lighting. Could you pull the frame out a bit? It's probably just held in place by the rubber stopper.

Jochen_145 wrote:

Only when a passive sensor is connected. Therefore, do not connect any pull-up resistors to an analog input pin (IDR). Quote: Are there any passive LD systems at all in the automotive sector? I'm not familiar with any such feature at OEM, but I could imagine that the French might use one. Otherwise, I can't imagine how you came up with the idea that the analog inputs in the MSG are equipped with pull-up resistors. You usually only find this feature in digital inputs, if at all.

A pull-up resistor has no influence on any inversion or anything else. There is a 10k ohm resistor on terminal 15 or on the switching relay for the MSGR. The current flow does not affect the active output of the sensor. However, with the French, for example, there are separate error codes for open circuits or short circuits; it's possible that VAG hasn't provided anything specific for that, as it's mainly for diagnostic purposes. The sensor showed no detectable change in its output voltage when measured with a 4-digit meter under a 5mA load change. This issue only affects older Euro3 PSA diesel engines equipped with the EDC15 system.

There is also a simple risk that if a signal cable is damaged or broken and has a slight voltage applied due to electrolysis, the MSGR's FET input may not be able to detect an anomaly during the self-diagnosis process before starting. And again, this resistance only affects the system when there is a power outage.

Incidentally, the term "electronic short circuit" is used only when there is an overload in a circuit. Therefore, in the instrument, a pull-up resistor for a strain gauge or for diagnostics (which is probably not needed in this device) is built in, and the resistance is calculated so that there is no overload in the sensor signal relative to ground. Similarly, if the input is completely high-impedance.

If the current flowing through the instrument is in the range of a few milliamperes, there is nothing against testing it with the original load cells. If a sensor with a voltage divider principle, as you described (strain gauge with a resistance bridge circuit), is used, it is important to determine the current of the internal pull-up resistor, as this forms the second part of the measurement bridge for a passive sensor. If the currents are not as low as those of a tank level sensor, there is nothing against trying it. At least from the electronic side.

hi,

"On the advertisement page, it says:"

"VDO MADE IN GERMANY, WEIGHTLESS."
"350.271/002/044 - 12V - 10/91"


The small blue stamp imprint on the back, located between the lighting contacts and the right mounting screw, reads:

"N12|10.91"

Unfortunately, I don't have any information at all, not even any documents.

Thank you very much for your efforts.

Best regards.