Testing power supply relay for Motronic system: Audi 4.2 (AHK)
Step-by-step testing power supply relay for Motronic system for the Audi 4.2 (AHK): factory workshop text.
Workshop procedure for AUDI — the factory write-up, straight from real workshop data.
🔧 Engine codes this applies to
📋 Procedure
The power supply relay -J271 is located in the front passenger footwell (A pillar).
=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder
Voltage for the following components is supplied via this relay:
Injectors
Engine control unit -J220
Solenoid valve for activated charcoal filter -N80
Intake manifold changeover valve -N156
Testing the power supply relay
Remove power supply relay -J271 from the relay base.
Connect diode test lamp V.A.G 1527 between contact 2 (positive, terminal 30) and engine earth.
Connect diode test lamp V.A.G 1527 between contact 4 (positive, terminal 30) and engine earth.
The diode test lamp should light up in each case.
If the diode test lamp does not light up, test the wiring connection for open circuit.
=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder
Connect diode test lamp V.A.G 1527 between contact 2 (positive, terminal 30) and contact 6 (earth signal from engine control unit -J220).
Switch ignition on.
The diode test lamp should light up.
If the diode test lamp does not light up:
Switch off ignition.
Connect test box V.A.G 1598/19 to wiring harness for engine control unit =>Page
24-14
.
Test wiring connection from contact 6 at relay base to socket A2 of the test box for open circuit.
=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder
If there is no open circuit and the diode test lamp still does not light, replace the engine control unit => Page
24-15
.
Plug in the power supply relay at the relay base.
Connect the wiring loom to the engine control unit.
Remove the fuse for the engine control unit and/or the injectors.
Remove the fuse for ACF solenoid valves -N80 and/or -N156.
Switch ignition on.
Connect diode test lamp to engine earth and to one of the two fuses in each case.
The diode test lamp should come on as both fuses are conducting voltage at one of the contacts.
If the diode test lamp does not come on for one or both fuses, test the wiring connection from the fuses to contact 8 at the relay position for the power supply relay for open circuit.
=> Current Flow Diagrams, Electrical Fault-finding and Fitting Locations binder
If there is no open circuit in the wiring, replace power supply relay -J271.
Refit the fuses.
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.