Electronic Throttle Body (ETB)

The Gen II electronic throttle body has the following characteristics:

1. The DC motor is driven by the PCM (requires 2 wires). The gear ratio from the motor to the throttle plate shaft is 17:1.
2. Two springs are used: one is used to close the throttle (main spring) and the other is in a plunger assembly that results in a default angle with no power applied. This is for limp home reasons (the force of the plunger spring is 2 times stronger than the main spring). The default angle is usually set to result in a top vehicle speed of 48 km/h (30 mph). Typically this throttle angle is 7 to 8 degrees from the hard-stop angle.
3. The closed throttle plate hard stop is used to prevent the throttle from binding in the bore (~0.75 degree). This hard stop setting is non-adjustable and is set to result in less airflow than the minimum engine airflow required at idle.
4. Unlike cable type throttle bodies, the intent for the ETB is to not have a hole in the throttle plate or to use plate sealant. The hole is not required in the ETB because the required idle airflow is provided by the plate angle in the throttle body assembly. This plate angle controls idle and idle quality and eliminates the need for an IAC valve.
5. The system has 2 throttle position sensors. Redundant throttle position signals are required for monitor reasons. The TP1 has a negative slope (increasing angle, decreasing voltage) and the TP2 has a positive slope (increasing angle, increasing voltage). During normal operation the negative sloped TP sensor (TP1) is used by the control strategy as the indication of the throttle position. The TP sensor assembly requires 4 wires:

• 5 volt reference voltage (ETCREF)
• Signal return (ETCRTN)
• TP1 voltage with negative voltage slope 5 volts to 0 volts
• TP2 voltage with positive voltage slope 0 volts to 5 volts