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Problem with atmospheric pressure sensor in the control unit for T4 2.5 TDI ACV

 
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Blaumann
Blaumann


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Post15-07-2019, 16:33    Subject: Problem with atmospheric pressure sensor in the control unit for T4 2.5 TDI ACV Quote

Hello.
I'm experiencing occasional, minor power issues with our 1998 ACV. VCDS lite has been displaying the error code 65535 - "Control unit defective" for some time.
When I look at MWB 10 field 2 (ambient pressure), I usually see a fixed value of 695 mBar. Occasionally, it jumps to plausible values just below 1000 mBar. And recently, the values have also increased significantly, reaching up to 1300.
I suspect that the pressure hose to the turbocharger pressure sensor has burst (I've experienced this before with a Golf 3 TDI). If I'm opening it up anyway to replace the pressure hose, I'd like to replace the atmospheric pressure sensor or at least resolder it.
Where on the circuit board can I find it?
Is the sensor available individually, or is there a suitable replacement part? Or is resoldering usually sufficient? Sometimes the sensor still provides plausible values.
Thank you very much, and best regards.
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Rüdi
Profi-Schrauber
Profi-Schrauber


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Location: Nord/Osthessen
2001 Audi A4 Avant
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Post15-07-2019, 18:12    Subject: Problem with atmospheric pressure sensor in the control unit for T4 2.5 TDI ACV Quote

https://cschirp.de/index.php/auto/map-sensortausch.html

"On my first Galaxy TDI, I replaced the original sensor with a fixed-value one because I needed a quick solution. I set it to just under 1000 mbar and that was it. Since it never went into the mountains, that was the simplest solution. I never changed it back, because the engine control unit (ECU) was so difficult to remove."
Sommer: A4 B5 Avant 2,5 TDI Quattro Facelift (AKN silber)

Wartet auf H Kennzeichen: A4 B5 Avant 1.9 TDI Quattro (AFN Schwarz)

Winter: A4 B5 Avant TDI Quattro (AFN rot)

Alltags Spardose: Audi A2 1.4 TDI (AMF Silber)
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Pölscheich
Blaumann
Blaumann


Joined: 11/09/2003
Posts: 69
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Post21-07-2019, 10:32    Subject: Solved (for now): Likely a cold solder joint Quote

Hi.
Based on the images in the link, I identified the part, and based on the information that the problem disappeared after soldering measurement cables, I simply resoldered the connections.
Currently, I'm getting plausible readings again (969 mbar at home, down to 941 mbar during a trip to a higher altitude).
Besides replacing the expectedly defective pressure hose to the turbocharger pressure sensor, the car is now running smoothly again.
Thank you very much.
Greetings.
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