Fuel Pump, Checking
Fuel Pump, Checking
=> [ Function and Voltage Supply, Checking ]
=> [ Fuel Pressure, Checking ]
=> [ Fuel Pressure, Checking while Driving ]
=> [ Residual Pressure, Checking ]
=> [ Fuel Delivery, Checking ]
=> [ Current Draw, 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)
• Multi-meter (V.A.G 1715)
• Wrench (T10202)
• Torque Wrench (40-200 Nm) (V.A.G 1332)
• Measuring Container, 2 Liter
Function and Voltage Supply, Checking
Test Conditions:
• Battery voltage at least 11.5 volts.
• Fuel pump control module (J538) fuse is OK
• Fuel pump control module is OK
Test Sequence:
• Fuel pump function is checked via the output Diagnostic Test Mode (DTM).
- Connect the vehicle diagnostic tester as follows:
- Connect the diagnostic cable connector to the Data Link Connector (DLC) in the driver's footwell.
- Turn on the ignition.
- Press the Vehicle Self-Diagnosis, Engine Electronics and Output Diagnostic Test Mode buttons on the display.
- Press the right arrow button o the display until output diagnostic test mode for the fuel pump electronics is reached.
Fuel pump must now accelerate slowly up to maximum RPM.
• Fuel pump runs quietly.
- Turn off the ignition.
If the Fuel Pump does not Start:
- Remove the rear seat bench.
- Disconnect the connector from the fuel pump control module.
- Check the voltage supply between terminals - 1 and 6 - using (V.A.G 1715).
• Specified value: approximately battery voltage
Voltage Supply not OK:
- Locate and repair the open circuit in the wiring using the wiring diagram.
Voltage Supply OK:
- Remove the cover - 1 - with fuel pump control module - 2 - from the fuel delivery unit.
- First, pull on the connector - arrow - without pressing the retainer to make sure it is connected securely. 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.
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. Then, disconnect the connection carefully to release the pressure.
- Remove the fuel lines - 1 and 2 - from the flange.
• Press in the securing ring to disengage the fuel lines.
- Remove the lock ring using wrench (T10202).
- Check whether the electrical wires between the flange and fuel pump are connected.
If No Open Circuits are Found:
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
Fuel Pressure, Checking
• If there are concerns about driving behavior, the fuel pressure can be checked during a road test. Refer to => [ Fuel Pressure, Checking while Driving ].
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. Then, disconnect the connection carefully to release the pressure.
- Disconnect the supply line (metal coupling) - arrow - and collect the leaking fuel in a cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut-off valves are open.
- Activate the fuel pump with the output Diagnostic Test Mode (DTM) to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Specified value: 4.0 to 7.0 bar
If the fuel pressure is OK, check the residual pressure. Refer to => [ Residual Pressure, Checking ].
If the Specification is Exceeded:
- Check the return line between the fuel filter and fuel pump (FP) for kinks and blockage.
If No Malfunction can be Found:
- Pressure relief valve in the fuel filter is malfunctioning, replace fuel filter.
If the Specification is not Obtained:
- Check the fuel pressure before the fuel filter as follows:
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) between the fuel filter and fuel supply line using (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut-off valves are open.
- Start the engine and run at idle speed.
- Slowly close the shut-off valve - A -. Pressure must increase to a minimum of 7.0 bar. If 7.0 bar is reached, open the shut-off valve again immediately!
If the Pressure has Increased:
- Replace the fuel filter, the fuel pump is OK but the pressure relief valve in the fuel filter is faulty.
If the Pressure does not Increase:
- Replace the fuel delivery unit, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
Fuel Pressure, Checking while Driving
• If there are concerns about the driving behavior, the cause may be low fuel pressure. Malfunctions in the high pressure area can also be caused by low fuel pressure. This test checks the high and low fuel pressure while driving. The high fuel pressure is read from the Engine Control Module (ECM). The pressure tester (VAS 6550) measures the low fuel pressure and transmits the reading to the vehicle diagnosis and service system (VAS 5052 B).
• This test can be a component of "Guided Fault Finding" if there is a Diagnostic Trouble Code (DTC) entry. It can also be started in the vehicle diagnosis and service system (VAS 5052 B) under "Function and Component Selection".
Special tools, testers and auxiliary items required
• Pressure gauge (VAS 6550)
• Hose adapter (6550/2)
• Vehicle diagnosis and service system (VAS 5052 B)
• Cable Set (VAS 5051/66)
The fuel supply line is under pressure! Wear eye protection and protective clothing in order to avoid injuries by contact with fuel. Before disconnecting the connection, wrap a cloth around the connection. Then, disconnect the hose connection carefully to release the pressure.
- Remove the fuel supply line (metal coupling) - arrow - and absorb the leaking fuel with a cleaning cloth.
• Press in the securing ring to disengage the fuel line.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/2).
- Lay a cleaning cloth on the engine cover. Lay the (VAS 6550) on the clean cloth and secure with cable ties - arrows -.
Secure the (VAS 6550) carefully so that it does not slide back and forth during the road test. Make sure there is enough clearance to all moving or hot components.
- Secure the drain valve with a cable tie - arrow - so that it does not open.
- Connect the (VAS 5051/66) to (VAS 6550) and route it through the vehicle interior.
Route the (VAS 5051/66) carefully. Make sure there is enough clearance to all moving or hot components.
- Connect the (VAS 5051/66) to (VAS 5052 B) and turn the (VAS 6550) on.
If the fuel pressure test is done within "Guided Fault Finding", follow the instructions from the vehicle tester.
If the fuel pressure test is done without "Guided Fault Finding", proceed as follows:
- Connect the (VAS 5052 B) to the vehicle.
- Select "Guided Fault Finding" in (VAS 5052 B).
- Perform the vehicle identification.
- Select the following menu items one after another using the Go to button:
• Function/Component Selection
• Powertrain
• Engine
• 24-Fuel Preparation/Injection
• Mechanical Components
• High Pressure Pump
- Follow the instructions from the (VAS 5052 B).
Always secure testing and measuring equipment on the rear seat during a road test.
This equipment should only be operated by a passenger when driving.
Residual Pressure, Checking
• Fuel pressure is OK and the pressure tester (VAS 6550) is connected. Checking the fuel pressure. Refer to => [ Fuel Pressure, Checking ].
Test Sequence:
- Activate the fuel pump with the output Diagnostic Test Mode (DTM) to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Specified value: 4.0 to 7.0 bar
- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the Pressure drops Further:
- Activate the fuel pump with output DTM to build fuel pressure.
- Close the shut-off valve - B - on the (VAS 6550) as soon as pressure accumulates. The lever is perpendicular to the direction of flow.
If Pressure no longer Drops:
• Check for the leak on the engine side. Repeat the residual pressure check. Close the shut-off valve - A - this time to determine if there actually is a leak on the engine side.
- Check the fuel pipe to high pressure pump for leaks.
If no Malfunction can be Found:
- Replace the high pressure pump. Refer to => [ High Pressure Pump ] High Pressure Pump.
If the Pressure Drops Again:
Check for the leak on the fuel tank side. Proceed as follows:
- Check the fuel line to the fuel filter for leaks.
If no Malfunctions are found on Fuel Line:
- Check the pressure retention valve in the fuel delivery unit. Proceed as follows:
- Disconnect the fuel supply line - arrow - from the fuel filter.
- Connect the (VAS 6550) between the fuel filter and fuel supply line using (VAS 6550/1) and (VAS 6550/2).
- Make sure the drain is closed and the shut-off valves are open.
- Activate the fuel pump with the output DTM to build fuel pressure.
- Check the fuel pressure on the (VAS 6550).
• Specified value: 4.0 to 7.0 bar
- Close the shut-off valve - A - once pressure has increased.
- Watch the pressure decrease on the (VAS 6550). After 10 minutes the pressure must not drop below a 3.0 bar decrease.
If the Pressure Drops:
- The pressure retention valve in the fuel pump is faulty, replace the fuel delivery unit. Refer to => [ Fuel Delivery Unit ] Fuel System Components.
If the Pressure does not Drop:
- The pressure retention valve in the fuel pump is OK. The pressure relief valve in the fuel filter is faulty. Replace the fuel filter.
Fuel Delivery, Checking
- Remove the rear seat bench.
- Remove the cover - 1 - with fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First, pull on the connector - arrow - without pressing the retainer to make sure it is connected securely. 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 the battery positive clamp in the engine compartment.
• This step allows the fuel pump to run when the engine is not running.
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. Then, disconnect the connection carefully to release the pressure.
- Disconnect the supply line (metal coupling) - arrow - and collect leaking fuel in a cloth.
• Press in the securing ring to disengage the fuel lines.
- Connect the (VAS 6550) to the fuel supply line using (VAS 6550/2). Hold the other end of the (VAS 6550/1) in the measuring container.
- Make sure the drain is closed and the shut-off valves are open.
Danger of spraying. Wear protective goggles and protective clothing to prevent injuries and contact with skin. Hold the container in front of free the connection of pressure measuring device.
- Operate the (V.A.G 1348/3A). Slowly close the shut-off valve - arrow - until the (VAS 6550) shows 4 bar. From this point on do not move position of shut-off valve.
- Empty the measuring container.
- The fuel delivery rate of the fuel pump is dependent on battery voltage. Connect the (V.A.G 1715) to connectors - 1 and 5 - of (VAS 5565).
- Operate the (V.A.G 1348/3A) for 60 seconds and simultaneously the measure voltage at the fuel pump.
- Compare the quantity of fuel delivered with the specification.
**) Voltage at fuel pump with engine running in idle and the pump is on.
Example:
During the test, a voltage of 10.5 volts is measured. This results in a minimum delivery quantity of approximately 1,200 cm3 / 60 sec.
If the Specification is not Obtained:
- Check the fuel lines for possible restrictions (kinks) or blockages.
If no Malfunction can be Found:
- 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 the Specification 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. Then, disconnect the connection carefully 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 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 - arrow - until the (VAS 6550) shows 4 bar. From this point on do not move position of shut-off valve.
- Empty the measuring container.
- Repeat the fuel delivery test.
If the Minimum Delivery Rate is now Obtained:
- Replace the fuel filter.
If the 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.
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 seat bench.
- Remove the cover - 1 - with fuel pump control module (J538) - 2 - from the fuel delivery unit.
- First, pull on the connector - arrow - without pressing the retainer to make sure it is connected securely. 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 (VAS 5565) red wire with the word "current clamp" on it.
- Start the engine and run at idle speed.
- Measure the current draw of the 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, the fuel pump is faulty. Refer to => [ Fuel Delivery Unit ] Fuel System Components.