Checking engine control unit voltage supply: VW (AAC, AGZ)
Step-by-step checking engine control unit voltage supply for the VW (AAC/AGZ): factory workshop text.
Workshop procedure for VW — the factory write-up, straight from real workshop data.
📐 9 workshop diagrams for AAC
Real factory drawings for this job — timing marks, bolt locations and routing. Locked in the free view.
📋 Procedure
Special tools, testers, measuring instruments and auxiliary items required
V.A.G 1598/22 Test box
Hand multimeter V.A.G 1526 or multimeter V.A.G 1715
Fault reader V.A.G 1551 or vehicle system tester V.A.G 1552 with cable V.A.G 1551/3
Adapter set V.A.G 1594
Current flow diagram
Check conditions
The battery voltage must be at least 11.5 V.
Alternator must be OK
The fuses No. 10 and 29 must be in order.
Test sequence
Checking voltage supply via fuel pump relay (J17)
Connect fault reader V.A.G 1551 (V.A.G 1552) and select engine electronics control unit with the "Address word" 01. When doing this the engine must be running at idling speed.
(Connecting fault reader and selecting engine electronics control unit => Page
01-4
.)
Rapid data transfer
HELP
Select function XX
Indicated on display:
Press keys 0 and 8 for the function "Read measured value block" and confirm entry with Q key.
Read measured value block
HELP
Input display group number XXX
Indicated on display:
Press keys 0, 0 and 4 for "Display group number 4" and confirm entry with Q key.
Read measured value block
4
⇒
1
2
3
4
Indicated on display:
(1...4 = Display zones)
Read off figure displayed in display zone 2.
Specification: At least 11.5 V constant
Press ⇒key.
Press keys 0 and 6 for the function "End output" and confirm entry with the Q key.
If the displayed figure fluctuates or the battery voltage is not attained:
Switch off ignition.
Connect test box V.A.G 1598/22 to control unit wiring harness.
Connect multimeter to measure resistance to socket 2 of the test box and vehicle earth.
Specification: Max. 1.5 ω
If the specification is not attained:
Check wiring according to current flow diagram.
Checking voltage supply via terminal 30
Check voltage with multimeter and aux. cables from V.A.G 1594 between test box sockets 2+3:
Specification: Min. 11 V
Checking voltage supply via terminal 15
Switch ignition on.
Check supply voltage between the test box sockets 1+2 with multimeter and adapter cables from V.A.G 1594:
Specification: Min. 11 V
If the specifications are not attained:
Check wiring according to current flow diagram.
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.