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Turbo control

Turbo control


The airflow from the turbocharger is regulated by a solenoid valve, which controls the exhaust turbine wastegate pneumatically.

The solenoid valve is powered from +15 and is grounded from control module pin 13 with a 32 Hz PWM. The turbocharger flow increases as the pulse ratio increases.

When the requested air mass/combustion is too great to be regulated by the throttle alone, the turbo control must supply the excess requirement. The excess is converted to a PWM, which controls the charge air control valve.

The value of the atmospheric absolute air pressure and the temperature of the intake air are used to correct the conversion. At low atmospheric pressures or when the intake air temperature is high, a greater PWM ratio is required to obtain the same air mass/combustion.

The control module then checks that the current air mass/combustion corresponds to that requested. If necessary, the PWM ratio is finely adjusted by multiplying it with a correction factor, charge air adaptation.

The correction factor is adapted at full throttle in the range 2400 - 4500 rpm. The engine speed should be within the adaptation range for more than 2 seconds. Charge air adaptation should be carried out in as high a gear as possible.

The correction factor (charge air adaptation) is stored in the control module memory and is always used to calculate the PWM ratio.

This is to ensure that the current air mass/combustion will correspond with the requested as soon as possible after a change in load. The limit for adaptation is 100%.

Diagnostics


• If there is an open circuit or short circuit to ground, diagnostic trouble code P1662 will be generated.

• If there is a short circuit to B+, diagnostic trouble code P1663 will be generated.

• If the air mass per combustion is higher than the requested, diagnostic trouble code P1549 will be generated.


System reaction to a fault


• Charge air adaptation is blocked.

• The requested air mass per combustion is limited to 600 mg/c.

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Note

The system regulates the current air mass/combustion so that it corresponds with the requested value. It is completely normal for the throttle not to be fully open despite the accelerator pedal being fully depressed.