Testing charge pressure control valve -N75: Audi 1.9 TDI (1Z, AHU)
Step-by-step testing charge pressure control valve -N75 for the Audi 1.9 TDI (1Z/AHU): factory workshop text.
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
Testing internal resistance
Switch off ignition.
Pull connector off charge pressure control solenoid valve -N75.
Connect multimeter to valve (resistance measurement range)
Specification: 25 ... 45 ω
If the specification is not obtained:
Renew charge pressure control solenoid valve -N75.
Testing voltage supply
Connect multimeter (voltage test range) between contact 2 and earth.
Switch on ignition.
Specification: approx. battery voltage
If the specification is not obtained:
Test wiring for open circuit and short to positive or earth.
=> Current flow diagrams, Electrical fault finding and Fitting locations
Testing control signal wiring
Switch off ignition.
Cut floor covering along lines as indicated -arrows- and fold back.
On vehicles with air conditioner, disconnect condensation hose
-arrow-.
Insert a screwdriver next to retainer clip between control unit support bracket and plastic holder.
Twist screwdriver as far as necessary to disengage lugs on support bracket (above retainer clip) from locating hole in plastic holder.
Pull control unit down slightly and remove screwdriver.
Pull control unit about 3 or 4 cm down. The control unit will engage in a second locating hole (service position).
Disengage retainer clip and unplug control unit connector.
Note:
Always make sure that the ignition is switched off before unplugging or fitting the connector for the diesel direct injection system control unit.
With the ignition switched off, connect test box V.A.G 1598/18 to connector -1- (the control unit -2- remains disconnected).
Test 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 is OK, fit a new engine control unit:
=> Diesel direct injection and glow plug system (TDI 4-cyl.); Repair group 23; Servicing diesel direct injection system; Renewing control unit for engine electronics
Diesel direct injection and glow plug system (TDI 4-cyl.)
Servicing diesel direct injection system
Renewing 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.
Ask about my car →Other AUDI procedures
- Removing and installing flywheel/drive plate
- Checking solenoid valve for boost pressure limitation -N75
- Testing intake air temperature sender -G42
- Testing oil pressure and oil pressure switch
- Testing modulating piston movement sender and quantity adjuster
- Removing and installing toothed belt – Audi · 56 torque figures
- Removing engine – Audi A8 D3 · 41 torque figures
- Removing camshaft timing chain from camshafts – Audi A6/A7 C7 · 38 torque figures
- Installing engine – Audi A8 D4 · 36 torque figures
- Removing and installing camshaft timing chain · 29 torque figures
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.