Check solenoid valve for boost pressure limitation -N75 — AUDI
Check solenoid valve for boost pressure limitation -N75 on Audi: factory workshop procedure for engines 1Z, AHU. Full factory text, tools and checks.
Workshop procedure for AUDI — the factory write-up, straight from real workshop data.
📋 Procedure
AHU
Special tools and workshop equipment required
V.A.G 1526 A
V.A.G 1594 A
V.A.G 1598/18
Checking internal resistance
Switch ignition off.
Unplug connector from solenoid valve for boost pressure control -N75.
Connect multimeter to injector to measure resistance.
Specification: 25...45 ω
If specification is not attained:
Replace solenoid valve for boost pressure control -N75.
Checking power supply
Connect multimeter between contact 2 and earth to measure voltage.
Switch the ignition on.
Specification: approx. battery voltage
If specification is not attained:
Test wiring for open circuit and short to positive or earth.
=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder
Testing control signal wiring
Switch ignition off.
Remove the lower part of the right A pillar trim and the front door sill panel tread strip
=> General Body Assembly; Repair group 70
General Body Assembly
Pull back floor covering at front of right footwell. (If necessary, cut open the perforated seam on the left with a knife.)
Unscrew bolts -arrows- for electronics box cover.
Carefully detach upper and lower sections of cover.
Pull out cross strut -arrow 3- with attached parts.
Screw out bolts -arrow 1- and -arrow 2-.
Remove engine control unit.
Disengage retaining clip and unplug control unit connector.
Note:
Always make sure that the ignition is switched off before unplugging or fitting the connector of the control unit for diesel direct injection system.
With the ignition switched off, connect test box V.A.G 1598/18 to connector -1- (the control unit -2- remains disconnected).
Check for open circuit and short to positive or earth in the following wiring connections:
Connector / Contact · Test box V.A.G 1598/18 / Socket
1 · 47
Rectify any open/short circuit as necessary.
If the wiring connection is OK, replace the engine control unit:
=> Diesel Direct Injection and Glow Plug System (TDI 4-cylinder); Repair group 23; Servicing diesel direct injection system; Replacing control unit for engine electronics
Diesel Direct Injection and Glow Plug System (TDI 4-cylinder)
Servicing diesel direct injection system
Replacing control unit for engine electronics
TorqFix answers live for your specific car — tell it the engine code and it serves the matching sequence, torque figures and wiring for that exact variant.
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
Seen a figure that does not match your manual? Write to us — we correct it and note when. support@torqfix.com
The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.