17964 - dealing with it long time, help needed

DangerDane

New member
Joined
Sep 18, 2022
Location
Denmark
TDI
01 VW Passat 3BG, 1.9 TDI [AVB]
I have been struggling with the dreaded 17964 error for some time now and I'm close to throwing in the spanner and swapping out the engine.

That was until last night where I thought we had at least a little breakthrough, even if that didn't clear the error or fixed it. But this is what we have found out so far.

- Turbo replaced with a secondhand one, which holds vacuum and can be pulled to 20 units of hg vacuum for full stop and holding

- can make around 1.1-1.2 bar absolute boost, but the demand is ~2.5 bar absolute pressure

- N75 only pulls around 5 units of hg vacuum and has been replaced with another unit that shows the same behavior. I have video

So we are "down" to concluding it might be somewhere in the vacuum system that there might be an issue. But is there some way that I can see or find what the vacuum pressure should be at various points in the system at certain points to troubleshoot.

One thing I certainly would like to know is what the inbound pressure is supposed to be when the N75 solenoid is supposed to be active so that I can check whether the inbound vacuum is correct.

Thanks for the help in advance.
 

DangerDane

New member
Joined
Sep 18, 2022
Location
Denmark
TDI
01 VW Passat 3BG, 1.9 TDI [AVB]
I believe you should have +20 in Hg on the vacuum pump side of the N75. Do you have VCDS?
Yes I do, this bit " - N75 only pulls around 5 units of hg vacuum and has been replaced with another unit that shows the same behavior. I have video" was checked while running Group 11 under 01 - Engine, or do you have other tests in mind ?
 

A4QTDI

Well-known member
Joined
Dec 26, 2021
Location
Canada
TDI
A4 TDI
You need to check vacuum at vacuum pump while running with vacuum gauge. Should be more than 20in/hg. No vcds test for this. Then check for vacuum at inlet of N75 with gauge. Use T fitting, should be same, 20in/hg. N75 valve connection should be top - vacuum from pump, middle - actuator, bottom - vent to airbox.
 
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