P1555

P1555
Charge Pressure Characteristic Curve - Upper limit exceeded

Function
The charge pressure regulation adjusts the throttle valve angle and the engine speed to a specified value. The Mass Air Flow (MAF) Sensor records the actual value. The signal calculated this way serves as a control value and is compared with the specified value. If a deviation exists it will be compensated.
The adjustment value control is used as a plus range modulated signal to trigger an electro-pneumatic valve (frequency valve).
The frequency valve varies the pressure in the membrane boxes for the waste gates between charge pressure and ambient pressure until the required waste gate position has reached the desired specified value.

Diagnostic conditions
Engine speed higher than 2800 1/min
Throttle valve position larger than 3/4 of wide open throttle.





Diagnostic procedure
Check and adjust waste gates of turbo charger
1. Remove cover frame of boost air cooler.
2. Remove hose between frequency valve and throttle body from throttle body.




3. Connect special tool 9160/1 to removed hose.




4. Use standard hose clamp to clamp off hose between frequency valve and intake pipe.




5. Attach dial gauge and dial gauge support VW 387 to turbo charger deflector plate (e.g. using a screw clamp).
- Place sensor pin of safety bracket.
- Use special tool 9160/1 to generate an excess pressure of 0.5 bar.
- The push rod must be lifted by 4 ± 0.5 mm; otherwise adjust lift by turning adjustment screws.

- Turning clockwise lift decreases
- Turning anti-clockwise lift increases