Audi Workshop Service and Repair Manuals

Checking fuel pump control unit -J538- - vehicles with 4-cylinder TFSI engine

Special tools and workshop equipment required

t	Hand-held multimeter -V.A.G 1526C-

t	Auxiliary measuring set -V.A.G 1594C-

t	Adapter cable -V.A.G 1598/39-

t	Test box -V.A.G 1598/42-

Procedure l  Battery voltage at least 12.5 V l  Fuse in fuse holder -S228- (position 28) OK. l  Ignition off. Checking voltage supply for fuel pump (from fuel pump control unit -J538-) Saloon: –  Detach trim in luggage compartment. –  If necessary, fold forward right backrest of rear seat bench. Avant: –  Remove left-side section of backrest (1/3 section) → Rep. Gr.72. –  Remove left-side trim in luggage compartment and anti-soiling tray → Rep. Gr.70.

All models: –  Unscrew cover for flange -arrows-.

–  Push back protective sleeve. –  Connect hand-held multimeter -V.A.G 1526C- (voltage test range) with probes and plug-in adapters from adapter set -V.A.G 1594C- between contacts -1- and -4-, as shown in illustration; the connector remains in place.   Note The connector contacts are numbered accordingly on the back of the connector. –  Start engine. l  Specification when starting and at idling speed: approx. 4 ... 5.7 V. –  Press accelerator pedal quickly to the floor and release again (short throttle burst). l  Specification: The voltage value should first increase slightly, then drop and eventually rise to the previous reading. If display differs from specification described above: –  Check voltage supply and activation of fuel pump control unit -J538-.

Checking voltage supply for fuel pump control unit -J538- –  Unplug electrical connector -arrow- on fuel pump control unit -J538-.

–  Connect multimeter between contacts -3- and -4- of connector to measure voltage. –  Switch on ignition. l  Specification: approx. battery voltage If specification is not obtained: –  Eliminate open circuit in wiring (refer to current flow diagram).

Checking activation of fuel pump control unit -J538- –  Connect multimeter for voltage measurement with measuring probes and plug-in adapters from auxiliary measuring set -V.A.G 1594C- between contacts -4- and -5-, as shown in illustration; the electrical connector remains in place.   Note The connector contacts are numbered accordingly on the back of the connector. –  Start engine. l  Specification when starting and at idling speed: approx. 5.0 V. –  Press accelerator pedal quickly to the floor and release again (short throttle burst). l  Specification: The voltage value should first increase slightly, then drop and eventually rise to the previous reading.

If display differs from specification described above: –  Switch off ignition. –  Connect the test box -V.A.G 1598/42- to wiring harness with adapter lead -V.A.G 1598/39-1- or adapter lead -V.A.G 1598/39-2-. Do not connect engine control unit. Connect earth clip of test box to negative terminal of battery → Rep. Gr.24.   Caution To prevent damage to electronic components, select appropriate measuring range before connecting measuring leads and observe test requirements.

–  Check for open circuit and short to positive or earth in the following wiring:

Connector Contact	-V.A.G 1598/42- Socket
-5-	B 27

–  Repair open circuit or short circuit in wiring (refer to current flow diagram). If no fault is found: –  Renew fuel pump control unit -J538-.