Fuel Pump: Service Precautions

Before Opening High Pressure Fuel Injection System


The fuel injection system is divided into a high pressure section (maximum approximately 150 bar) and a low pressure system (approximately 7 bar).

Before opening high pressure parts, for example removing high pressure pump, fuel rail, fuel injectors, fuel pipes or fuel pressure sensor (G247), fuel pressure in high pressure area must be reduced to a residual pressure of approximately 7 bar. The procedure for this is as follows.

High Fuel Pressure, Reducing

- Connect vehicle diagnosis, testing & info. system (VAS 5051B).

- Start engine and run at idle speed.

- Select engine electronics in OBD.

- Then select measured values read out.

- Select measured value block 140.

- With the engine running at idle, the fuel pressure will be displayed in display field 3.

• Specified value: between 35 and 45 bar

- Pry off the left cover on the instrument panel using special hook (3370) - arrow -.





- With the engine at idle, pull the fuse - SC 27 - in the fuse holder in the driver side instrument panel from the fuel pump control module (J538).





- Check the fuel pressure on the tester.

• The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel from the transfer fuel pump (G6).

- Switch the ignition off as soon as the fuel pressure drops to approximately 8 bar.

• The fuel pressure must not drop below 6 bar, because otherwise the engine will shut off (risk of catalytic converter damage).


The fuel lines will continue to be filled with fuel, but will no longer be under high pressure. To open fuel system, wear protective eyewear and clothing to prevent injuries and contact with skin.

Before opening the high pressure system, place a cloth around the connection.

- After reducing fuel pressure, place a clean cloth around the connection and open the high pressure system immediately. Escaping fuel must be absorbed.

Perform the following steps are completing all work:

- Install the fuse.

- Erase the DTC memory and, using guided fault finding, generate the readiness code in the engine control module vehicle diagnosis, testing and information system (VAS 5051B).