Fuel Pump, Checking
Special tools, test equipment and auxiliary items
- VAG 1348/3A remote switch with VAG 1348/32 adapter cable
- Multimeter (Fluke 83 or equivalent)
- VW 1594 connector test kit
Test requirements
- Fuse 28 OK
- Relay in position -4- in relay panel behind storage shelf OK
- Fuel filter in good condition
- Battery fully charged (at least 12 volts)
- Connect VAG 1348/3A remote switch with VAG 1348/32 adapter cable.
- Press remote switch.
- Fuel pump must run (pump will be audible)
NOTE: The pump is very quiet, make sure area is quiet while testing.
If the fuel pump does not run:
Front-wheel drive vehicles
- Remove cover for closing flange under luggage compartment liner.
All-wheel drive vehicles
- Remove rear seat bench.
- Remove cover for closing flange on right-side under rear seat bench.
All vehicles
- Carefully release 4-pin harness connector and disconnect.
- Set multimeter (Fluke 83 or equivalent) to 20 volt DC range. Using adapter wire from VW 1594 connector test kit connect to terminals -1- and -4- of harness connector.
- Press (and hold) remote switch and read voltage.
- Specified value: approx. Battery Positive Voltage (B+)
If the specified value is attained but the fuel pump does not run:
Front-wheel drive vehicles
- Mark fuel supply line -2- and return line -1- and disconnect from closing flange.
WARNING!
- Fire Hazard! Do not smoke, work near heaters or have anything in the area that could ignite the fuel or fumes.
- Fuel supply lines are under pressure! Before loosening any lines, cover the connection with a rag. Release the pressure by slowly separating the connection.
- Remove union nut using 3217 ring nut spanner.
- Remove closing flange with seal from tank opening.
All-wheel drive vehicles
- Mark fuel supply line -1- and fuel return line -2- and disconnect from closing flange.
- Remove closing ring for sender for fuel gauge using 3087 wrench.
- Remove closing flange and seal from tank opening.
All vehicles
- Make sure electrical connection between flange and fuel pump is good.
If there are no open circuits:
- Fuel pump is faulty
- Replace fuel pump module.
Checking fuel pump delivery
Test requirements
- Battery fully charged (at least 12 volts)
- VAG 1348/3A remote switch connected.
- Remove fuel filler cap.
- Remove engine cover.
WARNING!
- Fire Hazard! Do not smoke, work near heaters or have anything in the area that could ignite the fuel or fumes.
- Fuel supply lines are under pressure! Before loosening any lines, cover the connection with a rag. Release the pressure by slowly separating the connection.
- Disconnect fuel supply line (arrow) and use rag to catch escaping fuel.
- Connect VAG 1318 pressure gauge with VAG 1318/12 adapter to fuel supply line (arrow).
- Attach suitable hose to VAG 1318/11 adapter of pressure gauge and position open end of hose into measuring cup.
- Open shut-off valve of pressure gauge.
Handle must point in direction of flow (position -A-).
- Operate VAG 1348/3A remote switch and while keeping switch pressed, slowly close shut-off valve toward position -B-, until pressure gauge indicates 4 bar (58 psi). Leave shutoff valve in this position.
- Empty measuring cup.
- Fuel supply is dependent on battery voltage. Therefore connect multimeter (Fluke 83 or equivalent) together with adapter wire from VW 1594 connector test kit to vehicle battery.
WARNING! Fire hazard! Be careful to not create sparks when connecting or disconnecting battery terminals or electrical test equipment when the fuel system is or has been open.
- Operate remote switch for 30 seconds while measuring battery voltage.
- Compare quantity of fuel delivered to specified value.
Explanation of chart:
*) Minimum fuel supply cubic cm./30 s (cc in 30 seconds)
**) Voltage at fuel pump with engine not running and fuel pump running (approx. 2 volts less than Battery Positive Voltage, B+)
Example for reading chart:
During the test, the Battery Positive Voltage (B+) is 12.2 volts. Since the pump voltage is approx. 2 volts less than B+, the minimum amount of fuel delivered is 550 cubic cm./30 s (550 cc in 30 seconds).
If the minimum amount of fuel delivered is not attained:
- Check fuel lines for kinks or blockage.
- Continue checking as follows:
- Disconnect fuel supply hose -1- to fuel filter.
- Connect VAG 1318 pressure gauge with 1318/10 adapter to hose.
- Repeat fuel delivery test.
If the minimum amount of fuel delivered is attained:
- Replace fuel filter.
If the minimum amount of fuel delivered is NOT attained:
- Remove fuel pump module and check screen for dirt:
If no problems were found:
- Fuel pump is faulty; replace fuel pump module:
If the minimum amount of fuel delivered is attained but another malfunction in the fuel supply system is suspected (i.e. intermittent interruption of the fuel supply):
- Check fuel pump amperage as follows:
- Reconnect all fuel lines.
- Connect multimeter (Fluke 83 or equivalent) using induction clamp on green/yellow wire of wiring harness.
- Run engine at idle.
- Measure amperage of fuel pump.
- Specified value: maximum 8 Amps
NOTE: If the malfunction in the fuel pump is intermittent, the pump can also be checked during a road test; however a second technician is required.
WARNING!
- When driving or riding in an air bag-equipped vehicle, NEVER hold the scan tool or other test equipment in your hands or lap while in motion. Objects between you and the airbag increase the risk of injury in an accident.
- During a test drive in an airbag-equipped vehicle, test equipment must always be fastened to and operated from the rear seat by a second technician.
If the amperage reading is higher:
- Fuel pump is faulty, replace fuel pump module:
Checking fuel pump check valve
Test requirements
- VAG 1348/3A remote switch connected.
- VAG 1318 fuel pressure gauge connected to fuel supply line.
NOTE: With this test all of the fuel supply line connections from the fuel pump module to the connection point of the VAG 1318 fuel pressure gauge are tested for leaks.
- Close shut-off valve of pressure gauge.
Lever must be at right angle to direction of fuel flow position -B-.
- Operate remote switch briefly several times until approx. 4 bar (58 psi) of pressure is attained.
- If pressure built up is too high, carefully release pressure by opening shut-off valve of pressure gauge.
CAUTION! Before opening the shut-off valve of the pressure gauge, position a cup at the open end of pressure gauge to catch the fuel
- Observe falling pressure at pressure gauge:
Minimum pressure after 10 minutes
Engine cold 2.2 bar (32 psi)
Engine at operating temperature 3.0 bar (44 psi)
If pressure continues to fall:
- Check all connections for leaks.
If no problems are found:
- Fuel pump is faulty, replace fuel pump module: