Fuel Supply

Fuel Pumps, Checking

Test requirements

- Fuses nos. -13- and -14- (arrows) in E-box (plenum chamber, left) must be OK

- Fuel Pump (FP) relays I and II must be OK
1. Fuel Pump (FP) 2 Relay -J49-
(Fuel Pump, right)
2. Fuel Pump (FP) Relay -J17-
(Fuel Pump, left)
- Battery voltage must be at least 11.5 volts.
- All electrical consumers such as, lights and rear window defroster must be switched off.
- For vehicles with automatic transmission, selector lever must be in -P-.
- Parking brake must be engaged or else daylight driving lights will be switched on.
- Ignition switched off.
Observe safety precautions.
Observe rules for cleanliness.
Check function and voltage supply of fuel pumps.
Check delivery quantity, current pick-up, and check-valves of Fuel Pumps (FP).

Check function and voltage supply of fuel pumps

Recommended special tools and equipment
- V.A.G1526 multimeter or V.A.G1715 multimeter
- V.A.G1594 connector test kit
- Wiring diagram

Test sequence, Transfer Fuel Pump (FP) -G23-, right
Test sequence, Fuel Pump (FP) -G6-, left

- Remove Fuel Pump (FP) 2 Relay -J49-, right, from relay carrier, position C19.

NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.

- Bridge terminals 19d + 19e on relay carrier using appropriate adapter cables.
- Switch ignition on.

Transfer Fuel Pump (FP) -G23-, right, must start up.
- Switch ignition off.

If Fuel Pump (FP) runs:

- Check activation of Fuel Pump (FP) 2 Relay -J49-, right, -1- according to wiring diagram
- Erase DTC memory from Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If Fuel Pump (FP) does not run:
- Remove bridge from terminal 19e.
- Connect multimeter to terminal 19e + Ground (GND) of relay socket for voltage measurement.
- Switch ignition on.
Specified value: at least 11.5 V
- Switch ignition off.

If specified value is not obtained:
- Locate and repair open circuit using wiring diagram
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If specified value is obtained:
- Bridge terminals 19d + 19e on relay carrier using appropriate adapter cables.

- Disconnect 4-pin harness connector (arrow) left, next to fuel tank, at vehicle floor.

- Connect multimeter to terminals 3 + 4 of connector for voltage measurement.
- Switch ignition on. Specified value: at least 11.5 V
- Switch ignition off.

If specified value is not obtained:
- Locate and repair open circuit using wiring diagram
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If specified value is obtained:
- Fuel Pump (FP), right, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory from Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

Test sequence, Fuel Pump (FP) -G6-, left

- Remove Fuel Pump (FP) Relay -J17-, left -2-, from relay carrier, position A6.

NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.

- Bridge terminals 6d + 6e on relay carrier using appropriate adapter cables.
- Switch ignition on.

Transfer Fuel Pump (FP) -G6-, left, must start up.
- Switch ignition off.

If Fuel Pump (FP) runs:

- Check activation of Fuel Pump (FP) Relay -J17-, left, -2- according to wiring diagram
- Erase DTC memory from Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If Fuel Pump (FP) does not run:
- Remove bridge from terminal 6e.
- Connect multimeter to terminal 6e + Ground (GND) of relay socket for voltage measurement.
- Switch ignition on.
Specified value: at least 11.5 V
- Switch ignition off.

If specified value is not obtained:
- Locate and repair open circuit using wiring diagram
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If specified value is obtained:
- Bridge terminals 6d + 6e on relay carrier using appropriate adapter cables.

- Disconnect 4-pin harness connector (arrow) left, next to fuel tank, at vehicle floor.

- Connect multimeter to terminals 1 +2 of connector for voltage measurement.
- Switch ignition on.
Specified value: at least 11.5 V
- Switch ignition off.

If specified value is not obtained:
- Locate and repair open circuit using wiring diagram
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

If specified value is obtained:
- Fuel Pump (FP), left, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

Check delivery quantity, current pick-up, and check-valves of Fuel Pumps (FP)

Test requirement
- Function and voltage supply of fuel pumps OK

Recommended special tools and equipment
- T10202 Wrench
- V.A.G 1318 Pressure gauge
- V.A.G 1318/7 Adapter
- V.A.G 1318/9 Valve adapter
- V.A.G 1318/13 Hose adapter
- V.A.G 1318/17 Adapter

- V.A.G1331 torque wrench (5 to 50 Nm)
- V.A.G1332 torque wrench (40 to 200 Nm)
- V.A.G1348/3A remote control with V.A.G1348/3-3 adapter cable
- V.A.G1594A connector test kit
- V.A.G1715 multimeter
- VAS5024A assembly tool for spring-type clamps

- VAS 5226 Suction pump

Not illustrated:
- V.A.G 1318/20 Adapter
- V.A.G 1318/20-1 Adapter
- Measuring container
- Wiring diagram

Checking fuel delivery
Observe safety precautions.
Observe rules for cleanliness.
- Remove fuel filler cap from fuel filler tube.

- Thread adapter (V.A.G 1318/20-1) on adapter (V.A.G 1318/20).
- Turn valve at T-piece (arrow) counterclockwise until it is completely open.

WARNING: Fuel supply line is under pressure. Before opening fuel system, connect Diesel extractor and release pressure.

- Remove protective cap for bleeder valve on fuel rail.

- Connect adapter (V.A.G 1318/20) with adapter (V.A.G 1318/20-1) and diesel extractor (VAS 5226) to bleeder valve -1-.
- Turn valve (at T-piece) clockwise into bleeder valve to stop.
- When fuel pressure is released, fuel system can be opened.

Checking fuel delivery:
- Transfer Fuel Pump (FP) -G23-, right
- Fuel Pump (FP) -G6-, left

Supply quantity of Transfer Fuel Pump (FP) -G23-, right, checking

- Remove Fuel Pump (FP) 2 Relay -J49-, right, from relay carrier, position C19.

NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.

- Connect V.A.G 1348/3A remote control with adapter V.A.G 1348/3-3 to connector arrow) of Fuel Pump (FP) relay for right Fuel Pump (FP).
- Connect remote control alligator clip to plus pole in engine compartment.

- Disconnect fuel supply line -1- from fuel distributor.
- Place hose -1- in a measuring container -2- of at least 1000 cu.cm.
- Measuring container must be emptied before measurement.
- Operate remote control for 15 seconds:
a minimal delivery quantity of 800 cu.cm/15 seconds must be obtained.

Supply quantity of Fuel Pump (FP) -G6-, left, checking

- Remove Fuel Pump (FP) Relay -J17-, left -2-, from relay carrier, position A6.

NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.

- Connect V.A.G 1348/3A remote control to connector (arrow) of Fuel Pump (FP) relay for left Fuel Pump (FP) using V.A.G 1348/3-3 adapter.
- Connect remote control alligator clip to plus pole in engine compartment.

- Disconnect fuel supply line -1- from fuel distributor.
- Place hose -1- in a measuring container -2- of at least 1000 cu.cm.
- Measuring container must be emptied before measurement.
- Operate remote control for 15 seconds
a minimal delivery quantity of 800 cu.cm/15 seconds must be obtained.

If minimal delivery quantity is not obtained during one of the tests:
- Check fuel lines for possible restrictions (kinks) or clogging.

If lines are OK:
- Replace filter element in fuel filter.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply (e.g. sporadic loss of fuel supply):
- Check current pick-up of Fuel Pumps (FP).

Check current pick-up of Fuel Pumps (FP)
Check current pick-up of each individual Fuel Pump (FP) as follows:
- Re-connect all disconnected fuel lines.

- Cut through floor carpet from point -A- to point -B- in pre-cut area (arrows).

- Remove nuts -1- from cover. Remove backrest support -2- or mounting bracket if necessary.

- Connect multimeter with electrical current probe to wire of 4-pin connector terminal -1- (arrow) from wiring harness to Fuel Pump (FP), right.
- Start engine and let run at idle.
- Measure Fuel Pump (FP) current draw.
Specified value: max. 11 amperes

If current draw is exceeded:
- Fuel Pump (FP), right, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code
- Repeat test on Fuel Pump (FP), left.

If current draw is exceeded:
- Fuel Pump (FP), left, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

NOTE: If malfunction in fuel system is sporadic, test can also be performed during a road test, but a second person is required.

If special testing equipment is required during road test, note the following:
- Test equipment must always be secured to the rear seat and operated from there by a second person.

If test and measuring equipment is operated from the passenger seat, the person seated there could be injured in the event of an accident involving deployment of the passenger side airbag.

Checking check-valves of Fuel Pumps (FP)

Test requirement
- Remote control (V.A.G 1348/3 A) with adapter (V.A.G 1348/3-3) still connected.

Test sequence

NOTE: This test also checks the connections of the fuel supply line from Fuel Pump (FP) units to connection point of pressure gauge for proper seal.

- Now, connect pressure gauge (V.A.G 1318) with adapters (V.A.G 1318/20, V.A.G 1318/20-1, V.A.G 1318/9) and diesel extractor (VAS 5226) as shown to bleeder valve - 1-.
- Turn valve (at T-piece) clockwise into bleeder valve to stop.
- Open shut-off valve of pressure gauge, operate remote control briefly and thus bleed.

- Close pressure gauge shut-off valve (lever perpendicular to direction of flow).
- Operate remote control in short intervals until a positive pressure of approx. 4 bar has built up.

WARNING: Danger of spraying when opening shut-off valve; Diesel extractor must be connected.

- If excess pressure is built up, reduce pressure by carefully opening shut-off valve.
- Observe pressure drop on pressure gauge. Pressure must not fall below 3.0 bar.

If pressure drops:
- Check fuel lines and line connections to fuel tank for proper seal.

If no malfunctions are found in wires:

WARNING: Fuel supply line is under pressure. Before opening fuel system, connect Diesel extractor and release pressure.

- In addition, place a rag around separating point to catch escaping fuel.
- Remove pressure gauge with adapters.

Check-valve of Transfer Fuel Pump (FP) -G23-, right, checking

Test requirement

- Relays for electrical Fuel Pumps (FP) -1- and -2- must be removed from their positions.

NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.

Test sequence

- Unbolt seal of left flange (fuel filter) using T10202 wrench.
- Carefully pry off flange and raise it slightly.
- Disconnect connectors next to fuel filter.

WARNING:
- The fuel or fuel lines in fuel system can become very hot (danger of scalding).
- In addition, the fuel system is under pressure. Before opening the system, place rags around the connection area and release pressure by carefully loosening the connection.
- Wear protective goggles and protective gloves when working on the fuel system.

- Now remove supply line -2- that is coming from right Fuel Pump (FP) unit at fuel filter -1- .
- Let fuel in outlet -1- flow back into fuel tank.

- Close pressure gauge shut-off valve (lever perpendicular to direction of flow).

- Connect pressure gauge (V.A.G 1318) to adapters (V.A.G 1318/7, V.A.G 1318/13 and V.A.G 1318/17) as shown.

NOTE: Ensure that the connection of fuel supply line engages audibly when it is connected.

- Connect V.A.G 1348/3A remote control with adapter V.A.G 1348/3-3 to connector (arrow) of Fuel Pump (FP) relay for right Fuel Pump (FP).
- Connect remote control alligator clip to plus pole in engine compartment.
- Operate remote control in short intervals until a positive pressure of approx. 4 bar has built up.
- Observe pressure drop on pressure gauge. Pressure must not fall below 3.0 bar.

If pressure does not drop below 3.0 bar:
- Check the check-valve of the Fuel Pump (FP) -G6-, left.

If pressure drops to below 3.0 bar:

- Open shut-off valve of pressure gauge and let fuel flow back into fuel tank via V.A.G 1318/13 hose adapter.
- Fuel Pump (FP), right, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code

Check-valve of Fuel Pump (FP) -G6-, left, checking

Test sequence
Changing-over of pressure gauge for left Fuel Pump (FP):

- Open shut-off valve of pressure gauge and let fuel flow back into fuel tank via V.A.G 1318/13 hose adapter.

WARNING:
- The fuel or fuel lines in fuel system can become very hot (danger of scalding).
- In addition, the fuel system is under pressure. Before opening the system, place rags around the connection area and release pressure by carefully loosening the connection.
- Wear protective goggles and protective gloves when working on the fuel system.

- Now remove supply line -2- that is coming from left Fuel Pump (FP) unit at fuel filter -1-.

- Close pressure gauge shut-off valve (lever perpendicular to direction of flow).

- Connect pressure gauge (V.A.G 1318) to adapters (V.A.G 1318/7, V.A.G 1318/13 and V.A.G 1318/24) as shown.

NOTE: Ensure that the connection of fuel supply line engages audibly when it is connected.

- Connect V.A.G 1348/3A remote control to connector (arrow) of Fuel Pump (FP) relay for left Fuel Pump (FP) using V.A.G 1348/3-3 adapter.
- Connect remote control alligator clip of plus pole in engine compartment.
- Operate remote control in short intervals until a positive pressure of approx. 4.0 bar has built up.
- Observe pressure drop on pressure gauge. Pressure must not fall below 3.0 bar.

- Open shut-off valve of pressure gauge and let fuel flow back into fuel tank via V.A.G 1318/13 hose adapter.
- Remove pressure gauge with adapters.

If pressure drops to below 3.0 bar:
- Fuel Pump (FP), left, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data. Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Readiness Code