Safety Precautions
Safety Precautions
Note the following when working on the fuel system:
There is a risk of injury because the fuel is under very high pressure.
• Before opening high pressure area of the fuel injection system, fuel pressure must be relieved to residual pressure.
• To reduce remaining residual pressure, lay a clean cloth around the connector and carefully loosen connector.
Burn risk due to escaping fuel.
• Because the transfer fuel pump (G6) runs briefly when the battery is connected and the driver door is opened, the voltage supply to the fuel pump control module (J538) must be disconnected before opening the fuel system.
Risk of destroying electrical components when battery is disconnected.
• Observe measures when disconnecting battery.
• Only disconnect battery with ignition switched off.
- Disconnect battery.
Preventing Personal Injury and Damage to Injection and Ignition Systems
To prevent personal injury and damage to the injection and ignition system, observe the following:
• Do not touch or disconnect ignition coils with power output stages when engine is running or turning at starting RPM.
• The ignition must be switched off before connecting or disconnecting injection and ignition system wiring or tester cables.
• If engine is to be cranked at starting RPM without starting (for example for compression testing), disconnect connectors from ignition coils and from fuel injectors. After performing work, check and erase DTC memory.
• Only clean engine with ignition switched off.
• If electrical connectors were disconnected, faults are saved in ECM:
- Connect Vehicle Diagnosis, Testing and Information System (VAS 5051B).
- Start "Guided Functions" operating mode.
- Generate readiness code in ECM.
Test and Measuring Instruments during Test Drive
If special testing equipment is required during road test, note the following:
Distraction and improperly secured test equipment can lead to accidents.
Risk of passenger airbag deploying in an accident.
• Operating testing and measuring equipment while driving creates a distraction.
• There is an increased risk of injury due to unsecured testing and measuring equipment.
Always secure testers on the rear seat with a strap and have a second person on the rear seat operate them.
Working on Cooling System
Note the following when working on the cooling system:
Risk of scalding due to hot steam and hot coolant.
• When the engine is warm the cooling system is under pressure.
• To reduce pressure, cover coolant reservoir cap with cloth and carefully open.
Before Opening High Pressure Fuel Injection System
• The fuel injection system is separated into a high-pressure section (maximum approximately 120 bar) and a low-pressure section (approximately 6 bar).
• Before a component in the fuel injection system high pressure area is remove, the fuel pressure must be definitely reduced to a residual pressure of approximately 6 bar, as described in the following.
Special tools, testers and auxiliary items required
• Vehicle diagnostic, testing, and information system (VAS 5051B)
Procedure
- With the ignition off, connect the vehicle diagnosis, testing and information system (VAS 5051B) to the diagnostic connection using the diagnostic lead.
- Start engine and let run at idle.
Display on (VAS 5051B):
- Press the Vehicle Self-Diagnosis button - 1 - in the selection.
Display on (VAS 5051B):
- In selection - 1 -, press the "Engine electronics" vehicle system and continue by pressing the -> button.
Display on (VAS 5051B):
- In selection - 1 -, press the "Measured values" function and continue by pressing the -> button.
Display on (VAS 5051B):
- In button field - 1 -, press the 1 4 0 buttons for "Display group 140" and confirm the entry by pressing the Q button.
Display on (VAS 5051B):
- Check read-out for fuel pressure in fuel rail in display field - 3 -.
• A value of 35 to 45 bar is displayed when the engine is running at idle. The display shows the actual pressure in the fuel rail which is generated by the high pressure pump.
- Remove the right luggage compartment side trim.
- Remove the fuse 6 (on fuse panel F) (SF6) for the fuel pump control module (J538) in the fuse holder in the right of the luggage compartment.
Display on (VAS 5051B):
- With the engine still running, check the fuel pressure in fuel system display - 3 -:
• The fuel pressure decreases rapidly because the mechanical high pressure pump is no longer supplied with fuel by the electrical fuel pump.
- Switch the ignition off as soon as the fuel pressure drops below 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 rail will continue to be filled with fuel, but it will no longer be under high pressure.
Do not let fuel come into contact with skin.
• Wear protective eyewear and clothing when opening the fuel system.
• Lay clean cloths around the connection before opening the high pressure area to collect any fuel that leaks out.
- Loosen the wire at a connection immediately.
• If the high pressure system is not opened immediately, the pressure will increase because of post-heating.
Final procedures
- Insert fuse 6 (on fuse panel F) (SF6).
- Connect the vehicle diagnosis, testing and information system (VAS 5051B) while the ignition is switched off.
- Start "Guided Functions" operating mode.
- Generate the readiness code in the engine control module.