Fuel Supply
Fuel Pumps, Checking
Test requirements
- Fuses - 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) Relay - J17 -
(Fuel Pump, right)
2 - Fuel Pump (FP) 2 Relay - J49 -
(Fuel Pump, left)
- Battery voltage must be at least 11.5 volts.
- All electrical consumers such as, for example, 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).
Checking function and voltage supply of fuel pumps
Recommended special tools and equipment
- VAG1526 multimeter or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
Test sequence, Fuel Pump (FP) - G6 -, right
Test sequence, Transfer Fuel Pump (FP) - G23 -, left.
- Remove Fuel Pump (FP) Relay - J17 -, right, from relay carrier, position C20.
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.
Fuel Pump (FP) - G6 -, right, must start up.
- Switch ignition off.
If Fuel Pump (FP) runs:
- Check activation of Fuel Pump (FP) Relay - J17 -, right, - 1 - according to wiring diagram:
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If specified value is obtained:
- Fuel Pump (FP) - G6 - faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
Test sequence, Transfer Fuel Pump (FP) - G23 -, left
- Remove Fuel Pump (FP) 2 Relay - J49 -, left, 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) - G23 -, left, must start up.
- Switch ignition off.
If Fuel Pump (FP) runs:
- Check activation of Fuel Pump (FP) 2 Relay - J49 -, left, - 2 - according to wiring diagram:
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
If specified value is obtained:
- Transfer Fuel Pump (FP) - G23 -, left, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
Checking 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
- VAG1348/3A remote control with VAG1348/3-3 adapter cable
- V.A.G 1318 pressure gauge
- V.A.G 1318/7 adapter
- V.A.G 1318/13 adapter
- V.A.G 1318/17 adapter
- VAG1331 torque wrench (5 to 50 Nm)
- VAG1332 torque wrench (40 to 200 Nm)
- VAG1594A connector test kit
- VAG1715 multimeter
without illustration:
- Measuring container
- Wiring diagram
Checking fuel delivery
- Remove fuel filler cap from fuel filler tube.
First, reduce fuel pressure as follows:
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.
- Place a rag around separating point to catch escaping fuel.
- Remove fuel supply line (arrow).
When the fuel pressure is reduced:
- Tighten threaded connection again.
Checking fuel delivery:
- Fuel Pump (FP) - G6 -, right,
- Transfer Fuel Pump (FP) - G23 -, left,
- Fuel Pumps (FP) left and right.
Supply quantity of Fuel Pump (FP) - G6 -, right, checking
- Connect V.A.G 1348/3A remote control to connector (arrow) of Fuel Pump (FP) relay for right Fuel Pump (FP) using V.A.G 1348/3-3 adapter.
- Connect alligator of remote control to B+ connection - 1 -.
- Disconnect fuel supply line - 1 - from fuel distributor.
- Place hose in a measuring container - 2 - of at least 1000 cu.cm.
- Measuring container must be emptied before measurement.
- Operate remote control 15 seconds: a minimal delivery quantity of 800 cu.cm/15 seconds must be obtained.
Supply quantity of Transfer Fuel Pump (FP) - G23 -, left, checking
- 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 alligator of remote control to B+ connection - 1 -.
- Disconnect fuel supply line - 1 - from fuel distributor.
- Place hose in a measuring container - 2 - of at least 1000 cu.cm.
- Operate remote control 15 seconds: a minimal delivery quantity of 800 cu.cm/15 seconds must be obtained.
Supply quantity of both Fuel Pumps (FP), checking
- For this, now connect V.A.G 1348/3-3 adapter of remote control to connector of Fuel Pump (FP) Relay, left and right:
- Connector (arrow) of Fuel Pump (FP) Relay for right Fuel Pump (FP).
- Connector (arrow) of Fuel Pump (FP) Relay for left Fuel Pump (FP).
- Connect alligator of remote control to B+ connection - 1 -.
- Disconnect fuel supply line - 1 - from fuel distributor.
- Place hose in a measuring container - 2 - of at least 1000 cu.cm.
- Measuring container must be emptied before measurement.
- Operate remote control 10 seconds:a minimal delivery quantity of 800 cu.cm/10 seconds must be obtained.
If the minimal delivery quantity is not obtained during one of the tests:
- Check fuel lines for possible restrictions (kinks) or clogging.
If the lines are OK:
- Replace filter element in fuel filter.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
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).
Checking 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).
- Unscrew nuts - 1 - of 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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
- 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 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
NOTE: If malfunction in fuel system is sporadic, test can also be performed during a road test, but a second person is required.
Check valve of Fuel Pump (FP) - G6 -, right, checking
Check valve of Transfer Fuel Pump (FP) - G23 -, left, checking.
Test sequence
- Remove Fuel Pump (FP) Relay - J17 -, right, from relay carrier, position C20.
NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.
- Unbolt seal of left flange (fuel filter) using T10202 wrench.
- Carefully lever 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.
- Connect V.A.G 1318 pressure gauge as indicated.
NOTE: Ensure that the connection of fuel supply line engages audibly when it is connected.
- Close pressure gauge shut-off valve (lever perpendicular to direction of flow).
- Now connect V.A.G 1348/3A remote control to connector (arrow) of Fuel Pump (FP) relay for right Fuel Pump (FP) using V.A.G 1348/3-3 adapter.
- Connect alligator of remote control to B+ connection - 1 -.
- Operate remote control in short intervals until a positive pressure of approx. 4 bar has built up.
WARNING: Danger of spray when opening shut-off valve. Hold container in front of open connection on pressure gauge.
- 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 within 10 minutes.
If pressure does not drop:
- Check the check valve of the Transfer Fuel Pump (FP) - G23 -, left.
If pressure drops:
- Fuel Pump (FP), right, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes
Check valve of Transfer Fuel Pump (FP) - G23 -, left, checking
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.
Test sequence
- Remove Fuel Pump (FP) 2 Relay - J49 -, left, from relay carrier, position A6.
NOTE: Do not use metallic tools to pry off relays from relay carrier. The terminals could conduct electricity.
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 -.
- Let fuel in outlet - 1 - flow back into fuel tank.
- Connect V.A.G 1318 pressure gauge as indicated.
NOTE: Ensure that the connection of fuel supply line engages audibly when it is connected.
- Close pressure gauge shut-off valve (lever perpendicular to direction of flow).
- Now 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 alligator of remote control to B+ connection - 1 -.
- Operate remote control in short intervals until a positive pressure of approx. 4.0 bar has built up.
WARNING: Danger of spray when opening shut-off valve. Hold container in front of open connection on pressure gauge.
- 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 within 10 minutes.
- 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:
- Transfer Fuel Pump (FP) - G23 -, left, faulty, replace Fuel Pump (FP) unit.
- Erase DTC memory of Engine Control Module (ECM). Diagnostic Mode 04 - Erase DTC Memory
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes