Fuel Pump: Testing and Inspection
Fuel Pump, Checking
Special tools, testers and auxiliary items required
• Pressure Tester (VAS 6550)
• Remote Control (V.A.G 1348/3A)
• Test Instrument Adapter/DSO (5-pin) (VAS 5565)
• Handheld Multi-Meter (V.A.G 1526D) with
• Current Clamp (V.A.G 1526B/2)
• Wrench (T10202)
• Torque Wrench (40-200 Nm) (V.A.G 1332)
• Measuring container, 2 liter
• Vehicle Diagnostic Tester
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Delivery, Checking ]
=> [ Current Draw, Checking ]
=> [ Fuel Pump Check Valve, Checking ]
Function and Voltage Supply, Checking
• Fuel Pump (FP) Relay (J17) OK
• Battery voltage at least 11.5 V.
• Fuel pump fuse OK, fuse assignment.
• Fuel pump function is checked via output Diagnostic Test Mode (DTM).
• The engine must be started briefly before the output diagnostic test can be performed a second time.
- Connect the vehicle diagnostic tester - 1 - as follows:
- Connect the diagnostic cable - 2 - connector to the Data Link Connector (DLC) in the driver's footwell.
- Turn on the ignition.
- Press the Vehicle Self-Diagnosis, On Board Diagnostic (OBD), Engine Electronics and Output Diagnostic Test Mode buttons.
- Press the right arrow button => repeatedly until the fuel pump relay (J17) is activated.
The fuel pump (G6) must start pulsed.
- Turn off the ignition.
If Fuel Pump Does Not Start
- Remove the rear bench seat.
- Remove the cover from the fuel delivery unit.
- First pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. If the connector was not connected correctly, check the fuel pump function again.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Install the (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the (V.A.G 1526D) to the wires - 1 and 5 - on the (VAS 5565).
- Start the output DTM again and measure the voltage at the fuel pump.
• Specified value: approximately 2 Volts less than battery voltage.
Voltage Supply not OK
- Locate and repair the open circuit in the wiring using.
Voltage Supply OK
The fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting the connection, wrap a cloth around the connection. Carefully disconnect the hose connection to release the pressure.
- Remove the fuel lines - 1 and 2 - from the flange.
• Press in the securing ring to disengage the lines.
- Remove the locking ring using (T10202).
- Remove the locking ring using (T10202).
If no open circuits are found:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
Fuel Delivery, Checking
• Voltage supply OK.
• Fuel pressure regulator and residual pressure OK. Checking, refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.
• Fuel filter OK.
- Remove the rear bench seat.
- Remove the cover from the fuel delivery unit.
- First pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. If the connector was not connected correctly, it could cause a fault.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Install the (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the (V.A.G 1348/3A) to the (VAS 5565) and to the battery positive terminal.
• This work step allows the fuel pump to run when the engine is not running.
• The fuel pump delivery rate is measured at 4 bar. Measure the fuel pressure before measuring the delivery quantity. Refer to => [ Fuel Pressure Regulator and Residual Pressure, Checking ] Testing and Inspection.
The fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting the connection, wrap a cloth around the connection. Carefully disconnect the connection to release the pressure.
- Disconnect the return line - 1 - from the fuel pressure regulator.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550/1) to the fuel pressure regulator and hold the other end of (VAS 6550/1) in a measuring container.
- Operate the (V.A.G 1348/3A) approximately 5 seconds to fill the fuel filter.
- Empty the measuring container.
- The fuel pump delivery rate depends on the voltage. Connect the (V.A.G 1526D) to connectors - 1 and 5 - on the (VAS 5565).
- Operate the (V.A.G 1348/3A) for 30 seconds and measure the voltage.
- Compare the quantity of fuel delivered with specification.
*) Minimum delivery rate cm3/30 s
**) Voltage on the fuel pump with engine running in idle and the pump is on.
Example
During test, a voltage of 10.5 Volts is measured. This results in a minimum delivery quantity of approximately 580cm3/30 s.
If the specification is not obtained:
- Check supply line to the filter for possible restrictions (kinks) or clogging.
If the fuel line is OK:
- Remove the cap from the fuel filler neck and repeat the test. If the fuel delivery quantity is now reached, check the fuel tank ventilation.
If specified value is again not obtained:
- Check the fuel filter as follows:
The fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting the connection, wrap a cloth around the connection. Carefully disconnect the connection to release the pressure.
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) to the fuel supply line using the (VAS 6550/1). Hold the other end of the (VAS 6550/2) in the measuring container.
- Make sure the drain is closed and the shut-off valves are open.
- Operate the (V.A.G 1348/3A). Slowly close the shut off valve - A - until the (VAS 6550) reads 4 bar. From this point on do not move the position of the shut off valve.
- Empty measuring container.
- Repeat the fuel delivery test.
If the minimum delivery rate is now obtained:
- Replace fuel filter.
If minimum delivery rate is again not obtained:
- Remove the fuel delivery unit and check fuel strainer for contamination.
Only when up to now no malfunction has been detected:
- Replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.
- Reconnect all disconnected fuel lines.
- Bleed fuel supply system. Refer to => [ Fuel System, Bleeding ] Fuel System, Bleeding.
Delivery rate has been obtained, but malfunctions are still suspected in the fuel supply (for example, intermittent loss of fuel supply):
- Check the fuel pump current draw. Refer to => [ Current Draw, Checking ].
Current Draw, Checking
- Remove the rear bench seat.
- Remove the cover - arrows - from the fuel delivery unit.
- First pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. If the connector was not connected correctly, it could cause a fault.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Install the (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the current clamp - A - to the red wire of the (VAS 5565) with the word "current clamp" on it.
- Start the engine and run at idle speed.
- Measure current draw of fuel pump.
• Specified value: maximum 9 amps.
• The fuel pump starting current may be higher than the specified value briefly when starting the engine.
• If the malfunction in the fuel system only occurs sporadically, the test can also be performed during a road test. A second person is needed to do this.
If the current draw is exceeded:
- Replace the fuel delivery unit if the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Service and Repair.
Fuel Pump Check Valve, Checking
- Remove the rear bench seat.
- Remove the cover - arrows - from the fuel delivery unit.
- First pull on the connector - arrow - without pressing the retainer to make sure it is securely connected. If the connector was not connected correctly, it could cause a fault.
- Disconnect the connector.
- Check the contacts on the connector and the fuel delivery unit for damage.
- Install the (VAS 5565) between the connectors on the fuel delivery unit and cover.
- Connect the (V.A.G 1348/3A) to the (VAS 5565) and to the battery positive terminal.
The fuel supply line is under pressure! Wear protective goggles and protective clothing to prevent injuries and contact with skin. Before disconnecting the connection, wrap a cloth around the connection. Carefully disconnect the connection to release the pressure.
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/1). Hold the other end of the (VAS 6550/2) in a measuring container.
- Close the shut-off valve - A - on the (VAS 6550) so the lever is perpendicular to the direction of flow.
- Operate the (V.A.G 1348/3A) at short intervals, until a pressure of approximately 4 bar has built up.
Danger of spraying when opening the shut off valve; wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold container in front of free connection of pressure measuring device.
- If pressure builds up too high, lower excess pressure by carefully opening the shut-off valve.
- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3 bar decrease.
If the pressure drops further:
- Check the line connections for leaks.
If no fault is detected in the wiring:
- If the check-valve in fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Service and Repair.