Generic Scan Tool
Diagnostic Procedures
Fuel Pressure Regulator and Residual Pressure, Checking
Function
The fuel pressure regulator regulates the fuel pressure to constant 4.0 bar.
Special tools, testers and auxiliary items required
• Pressure gauge (VAG1318)
• Adapter (VAG1318/7)
• Adapter (VAG1318/10)
• Hose adapter (VAG1318/13)
Without illustration:
• Assembly tool for spring-type clamps (VAS5024A)
Test requirements
• Parking brake must be engaged or else daylight driving lights will be switched on.
• For vehicles with automatic transmission, selector lever must be in P position.
• Delivery quantity of Fuel Pumps (FP) OK, checking --> [ Fuel Pump, Checking ] Fuel Pump, Checking.
Test sequence
Observe Safety Precautions: --> [ Safety Precautions ] Safety Precautions
Observe Clean Working Conditions: --> [ Clean Working Conditions ] Clean Working Conditions
- Remove fuses - 13 - and - 14 - for activation of Fuel Pump (FP) Relay (J17) and Fuel Pump (FP) 2 Relay (J49) from fuse holder.
• Fuses - 13 - and - 14 - are located in fuse holder of E-box, in plenum chamber, left.
Reduce fuel pressure as follows:
CAUTION!
• The fuel or fuel lines in fuel system can become very hot (danger of scalding)!
• In addition, the fuel system is under pressure!Before opening the system, place rags around the connection area and release pressure by carefully loosening the connection!
• Wear protective goggles and protective gloves when working on the fuel system!
- Place a rag around separating point to catch escaping fuel.
- Remove fuel supply line (arrow).
When the fuel pressure is reduced:
- Tighten threaded connection again.
- Loosen spring clip and remove fuel supply line from connecting piece at fuel rail.
- Connect pressure gauge to supply line (VAG1318) and fuel rail using adapters (VAG1318/7), (VAG1318/10), and (VAG1318/13).
- Secure hose ends using clamps - 2 -.
• It is important that fuel hose ends are secured with clamps!
- Open shut-off valve of pressure gauge. The lever - 1 - points in the direction of flow.
- Insert fuses - 13 - and - 14 - in the fuse holder.
- Start engine and let run at idle.
- Measure fuel pressure.
Specified value: approx. 4.0 bar positive pressure
- Switch ignition off.
If specified value is not obtained:
- Check delivery quantity of Fuel Pumps (FP) --> [ Fuel Pump, Checking ] , Fuel Pumps (FP), checking.
- Replace fuel pressure regulator if necessary.
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.
If specified value is obtained:
- Now check for proper seal and residual pressure. Observe pressure drop on pressure gauge for this. After 10 minutes
at least 3.0 bar positive pressure should still be present.
If residual pressure falls below 3 bar positive pressure:
- Check pressure gauge for proper seal.
- Check check valves of Fuel Pumps (FP) --> [ Fuel Pump, Checking ] Fuel Pump, Checking.
When removing pressure gauge after completed test:
- Remove fuses - 13 - and - 14 - for activation of Fuel Pump (FP) Relay (J17) and Fuel Pump (FP) 2 Relay (J49) from fuse holder.
- Place a rag around separating point to catch escaping fuel.
- Remove fuel supply line (arrow).
When the fuel pressure is reduced:
- Tighten threaded connection again.
- Remove pressure gauge with adapters.
- Connect fuel supply line to connecting piece of fuel rail and secure it using spring clip.
- Insert fuses - 13 - and - 14 - in the fuse holder.
- Erase DTC memory of Engine Control Module (ECM) , Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code.