Checking low pressure on high-pressure pump, engines with supplementary fuel pump V393 — VW
Checking low pressure on high-pressure pump, engines with supplementary fuel pump V393 on VW: factory workshop procedure for engines CAAA, CAAB, CAAC.
Workshop procedure for VW — the factory write-up, straight from real workshop data.
📐 31 workshop diagrams for CAAA
Real factory drawings for this job — timing marks, bolt locations and routing. Locked in the free view.
📋 Procedure
Checking low pressure on high-pressure pump, engines with
supplementary fuel pump
V393
Note
The adapter lines/leads 1 to 4 listed below are not required for the test.
Hose
VAS 6551/1
Hose
VAS 6551/2
Test lead
VAS 6551/3
Test lead
VAS 6551/4
Note
To perform test, use
Vehicle diagnostic tester
in conjunction with
test instrument box
VAS 6356
.
Special tools and workshop equipment required
Pressure gauge
VAS 6551
Adapter set
VAS 6551/5
Instrument box
VAS 6356
Vehicle diagnostic tester
Laptop, vehicle diagnosis (remote head)
VAS 6150 A
Test prerequisites
Fuses must be OK.
Battery voltage at least 12 V
Ignition switched off
There must be at least 10 l of fuel in the fuel tank.
All electrical consumers, e.g. lights and rear window heating, must be switched off.
The fuel lines must not be kinked or damaged.
WARNING
Fuel supply lines are under pressure! Wear safety goggles and protective clothing to avoid possible injury and skin contact. Before opening hose connections wrap a cloth around the connection. Then release pressure by carefully pulling hose off connection.
Procedure
WARNING
Read rules for cleanliness and the instructions when performing any work on the fuel system.
Always follow these rules for cleanliness and instructions before starting work and while working on the fuel system.
Wrap a clean cloth around the connection before opening the fuel system, then carefully loosen the connection to release the pressure.
Loosen
spring-type clip
arrow
of fuel supply line
1
.
Pull off fuel supply line
1
from high-pressure pump
2
.
Collect escaping fuel with a cleaning cloth.
Insert
connection fitting
VAS 6551/5-1
into fuel supply line
1
and secure it with a clip.
Connect
hose
VAS 6551/2
between
connecting nipple
VAS 6551/5-1
and connection point
A
of
pressure tester (diesel)
VAS 6551
.
Connect
hose
VAS 6551/5-2
between connection
B
of
pressure tester (diesel)
VAS 6551
and high-pressure pump
2
.
Secure
hose
VAS 6551/5-2
to high-pressure pump
2
with a clip.
Switch on
pressure tester
VAS 6551
by pressing
On/Off
button.
Ensure that drain tap
C
on
pressure tester
VAS 6551
1
is closed.
Shut-off valves
A
and
B
on
pressure tester
VAS 6551
1
are open.
Connect
Vehicle diagnostic tester
to
test instrument box
VAS 6356
.
Activate fuel pump using guided function
“Fuel pump activation”
.
The fuel pump is activated.
Specification: ≥ 3.5 bar.
If the specified value is not reached: check fuel low-pressure ahead of fuel filter
Chapter
.
If test is
“OK”
:
Renewing fuel filter
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.