9-3 (9440) L4-2.0L Turbo (2007)
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Limp Home Throttle Valve: Description and Operation
Throttle Adjustment
1. Throttle motor
2. Throttle disc
3. Connector
The throttle disc is turned by a DC motor via a reduction gear. The motor is supplied from ECM with a PWM signal from pins 46(B), 63(B) and 47(B),
64(B). ECM can turn the throttle disc in both directions, i.e. open and close. A spring strives to keep the throttle slightly open.
When the throttle control goes into limp-home mode then it is this position that determines the throttle area and thereby controls the air mass/combustion
that can enter the engine. Fuel shut-off and ignition timing are used as control instruments in order to control the engine torque. The idling speed is
around 900 rpm. The engine will run erratically with low loads due to fuel shut-off. The car can still be driven but performance will be impaired.
Two throttle position sensors are connected to the shaft. The sensors comprise potentiometers supplied with 5V from ECM pins 30(B) and 31(B) and are
grounded to ECM pins 34(B) and 35(B).
The voltage from potentiometer 1 is connected to ECM pin 28(B) and increases as the throttle opens (increased area). The voltage from potentiometer 2
is connected to ECM pin 25(B) and drops as the throttle opens (increased area). The sum of the two voltages is therefore always 5V.
The value from potentiometer 1 is used by ECM to detect the current throttle opening (area).
The result of torque control is converted to air mass/combustion. Throttle control converts it to a certain requested value for throttle position sensor 1
and compares this requested value with the current value of the sensor. The difference (deviation) will give rise to a throttle motor PWM of a magnitude
and polarity that will turn the throttle until the desired value (area) is obtained. If a major fault arises in the throttle control then it will be shut down and
the throttle will go to a position of rest that is determined by a spring. Engine torque can now only be regulated using fuel shut-off and ignition timing.
