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Old 06-10-10, 23:23  
HOW TO - Test Charge Pressure Solenoid Valve AKA N75
simon6374 simon6374 is offline 06-10-10, 23:23

The N75 valve is like a switch controlling the turbo wastegate actuator. The wastegate itself is normally closed allowing exhaust gases to spin the turbo. When the wastegate actuator opens the wastegate, exhaust gases are diverted away from the turbo. This is necessary as excessive boost would result in engine damage.

The ECU uses the N75 valve to maintain correct boost levels by comparing readings from the MAP sensor (Manifold Absolute Pressure G71) with it's engine map. If the N75 fails to open the wastegate actuator the ECU triggers 'safe mode' limiting fuelling levels resulting in power loss. Always check the wastegate actuator and MAP sensor if you suspect a faulty N75 valve.



This graphic shows how boost pressure from the turbo is used by the N75 to regulate pressure to the wastegate actuator, as found on ACV AJT AYC AYY engines. It is important to appreciate that how it all looks and works will depend on the engine code, as there are different turbos and valves in use.



TESTING

Pull connector (1) off N75 valve (2)
Use a multimeter to measure resistance between valve contacts 2.
Spec ACV AJT AYC AYY = 25 to 45Ω
Spec AHY AXG AXL = 15 to 20Ω

Replace valve If spec not attained

If spec attained...
Switch on ignition and measure supply voltage at connector plug 1 and engine earth
Spec approx 12v. If spec not attained check wiring back to ECU.



ADDITIONAL NOTES
  • The N18 EGR solenoid valve is very similar to the N75 and has the same 2 pin connector plug. In fact, some engines use this type of valve for both functions (see graphic at end for AHY type engines). It is therefore possible to swap over all the pipes and plugs and use it to perform the job of an N75 valve. This is a useful way of checking the performance of N75 valve in addition to the above checks and can save you the cost of buying a replacement if you go for an EGR delete.
  • It is worthwhile replacing all the hoses to the N75 as it is very difficult to 'see' leaks and the rubber does deteriorate. I recommend using performance silicone hoses as they do not cost much more, come in a range of colours and are easier to slip on and off for maintenance.
  • Use a hand pump such as a 'mity vac' or similar to check wastegate actuator is working. Pull off actuator hose and connect pump directly to it. As you apply pressure the actuator rod should at some point begin to move until the wastegate is fully open.
  • Check vagcom for DTCs and check to see that the MAP sensor is working correctly.
  • A 'leaking' wastegate or 'faulty' actuator is not normally repairable and at present requires complete turbo replacement.






Last edited by JIMMYJAMES; 22-10-10 at 03:17.. Reason: Prefix HOW TO added.
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simon6374
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Re: HOW TO - Test Charge Pressure Solenoid Valve AKA N75
04-10-16, 13:32 #51
KendalT4
Van Man

Quote:
Originally Posted by Enduroclarky View Post
yesterday found the source of the problem..not the n75 valve,it was the n18 egr control solenoid, when I fitted the Allard delete pipe, I blanked the now redundant vacuum outlet from the n18, guess it was sucking and trying to implode itself, if you get what I mean. Removed the blanking bolt from the hose, and hey presto! the milking parlour has cleared off!! Cheers,
Iain.
Hi Enduroclarky,
Sounds like we have the same set up as you - I've got the EGR delete kit from Allard on mine and have both redundant hoses blanked off with bolts stuck in the ends - Has leaving the hose now open made a difference - if so did you unblock both hoses, or just the one - I spoke to Allard and they didn't think either would now do anything so could actually be removed completely?
We have issues of power loss up hills mainly, especially when cold. The hose to the wastegate actuator on the turbo looks iffy, so I'm going to swap that out too. I've got an intercooler to fit, but want to try and resolve any existing niggles before I do!
Cheers!
 
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Re: HOW TO - Test Charge Pressure Solenoid Valve AKA N75
27-11-16, 10:07 #52
t4granada
Van Rookie

Hello, I am new to posting on the forum so please forgive any mistakes etc., I will eventually get it right . I am the proud owner of a 2001 88 hp AJT 2.5 TDi, with about 165 k. on the clock. My query is about the possibility of the vacuum pump being faulty and hence not supplying enough suction, and this having an effect on the operation of the EGR and turbo wastegate; the reason for my question is that I have noticed a decrease in performance and general engine smoothness, exactly at the same time my brake assistance is almost gone (servo is OK, vacuum pump has been checked and provides very little suction-I am waiting for the replacement to arrive). Hoses and electrical connectors seem to be ok, so before I get into checking all that it would be great to know if there is a link there.
Thanks for the interest, and congratulations for a great forum.
Keep rolling
 
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Re: HOW TO - Test Charge Pressure Solenoid Valve AKA N75
04-12-16, 20:22 #53
sportline josh
Van Rookie

Hi guys i have a 2011 sportline bi turbo it has always done the mooing sound between 2/3rd gear but now does it for a few minutes after i switch the van off, im pretty sure someone said a biturbo will have two n75's is this right? does anyone recommend where to get the silicone pipes from?

cheers
 
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Re: HOW TO - Test Charge Pressure Solenoid Valve AKA N75
04-03-19, 04:41 #54
LoopSoosStroop
Van Expert

Hi Gents, hope you are well!

It seems that all the N75 valves available online look like the EGR one and not like the OEM AVC 2.5TDI one. Does anyone have a vacuum line diagram that shows how it must be connected?
 
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21-08-19, 19:05 #55
Spen1802
Van Pro

Great info
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