Auxiliary Fuel Pump -V393- OR Fuel Pump 2 -V277- INLINE ELECTRIC FUEL PUMP, CHECKING, ENGINE CODE CJAA
Special tools and workshop equipment required
- Diesel Pressure Tester KitVAS6551
- Diesel Pressure Tester Kit - Adapter Set VAS6551/5
- Vehicle Diagnostic Tester
Due to a software revision, the component name for the inline electric fuel pump was changed from "auxiliary fuel pump" to "fuel pump 2". They are the same component.
Test Conditions:
- The fuses must be OK.
- Connect the battery charger to make sure the voltage supply is minimum 12.5 V.
- Fuel tank minimum fuel level 15 liters.
- Make sure the vehicle is level.
- The fuel hoses and lines inside the engine compartment and on the underbody are not closed due to damage (bent).
- All electrical consumers such as, for example, headlamps and rear window defogger, must be off.
The vehicle must be fueled with diesel fuel treated for the season. Diesel fuel bought in the summer can be filtered to 0 °C (32 °F). The diesel fuel bought during the transition time can be filtered to -10 °C (14 °F) and fuel bought in the winter can be filtered to -20 °C (-4 °F). Under some conditions, summer diesel fuel can coagulate at low winter temperatures. If not sure, take a sample of the winter fuel and let it stand at low outside temperatures for approximately 1 hour. If the fuel coagulates at temperatures down to -20°C, then this diesel fuel is not suited for low temperatures. This coagulation can plug the screen in the fuel delivery unit as well as in the fuel filter.
Test Sequence
-- Follow all safety precautions. Refer to SAFETY PRECAUTIONS .
-- Follow the guidelines for clean working conditions. Refer to PARKING/AUXILIARY HEATER AND FUEL SYSTEM CLEAN WORKING CONDITIONS .
-- Remove the engine cover. Refer to ENGINE COVER .
-- Open the clamp and remove the fuel supply line -arrow- from the high pressure pump.
The fuel supply line remains under pressure. Wear protective eyewear and protective clothing in order to avoid injury and contact with the skin. Wrap a cloth around the connection before loosening hose connections. Remove the hose connection carefully to release the pressure.
-- Insert the Diesel Pressure Tester Kit - Adapter Set - Adapter 1VAS6551/5-1 into the supply line and secure with a clamp.
-- Connect the Diesel Pressure Tester Kit - Hose 2VAS6551/2 between the Diesel Pressure Tester Kit - Adapter Set - Adapter 1VAS6551/5-1 and the connection >>A<< of the Diesel Pressure Tester KitVAS6551.
-- Connect the Diesel Pressure Tester Kit - Adapter Set - Connection Hose 2VAS6551/5-2 between the connection >>B<< of the Diesel Pressure Tester KitVAS6551 and the high pressure pump. Secure the high pressure pump with one clamp.
-- Press the On/Off button to switch on the Diesel Pressure Tester KitVAS6551.
-- Open the shut-off valves -A- and -B- on the Diesel Pressure Tester KitVAS6551 in the direction of flow.
-- Close cut-off tap -C-.
-- Connect the Vehicle Diagnostic Tester and perform Guided Functions "check electric fuel pump(s)".
The fuel pump now runs for 30 seconds.
- Specified value: minimum 3.5 bar
If the specification is not obtained:
Check the connections between pressure gauge and fuel line for leaks.
Check pressure tester for leaks.
Check fuel lines and their connections for leaks.
If faults are found:
-- Check the fuel pressure from the Transfer Fuel Pump -G6-. Refer to Transfer Fuel Pump -G6- FUEL PRESSURE, CHECKING, ENGINE CODE CJAA .
-- Check the fuel delivery rate from the transfer fuel pump -G6-. Refer to Transfer Fuel Pump -G6- FUEL DELIVERY RATE, CHECKING, ENGINE CODE CJAA .
If the target values for the Transfer Fuel Pump -G6- are reached:
-- Replace the Auxiliary Fuel Pump -V393- or Fuel Pump 2 - V277-.