Understanding the EFI Process


Other Control System Calibrations; Throttle-By-Wire, EGR, Idle Control, etc.

toyota drive by wire throttle

The Throttle By-Wire (TBW) aka Drive-By-Wire (DBW) systems appears to be more complex than they actually are due to the redundancy which is built into the systems for safety reasons. Most TBW systems contain four major components; (1) the Throttle Actuator Control Relay, (2) the Drive Circuit for the throttle actuator which is located inside the ECU, (3) the Accelerator Pedal Position (APP) assembly, and (4) the Electric Throttle Body Assembly. With the implementation of the TBW system, manufacturers were able to eliminate the Idle Air Control (IAC) system because they were able to use the electronic throttle body to control the engine’s deceleration and idle. The above diagram will demonstrate the basic TBW system operation, please notice that each sensory component of the TBW system has 6 wires connected to it; we will later explain what each of these wires are for.

 The first part of this system is the Throttle Actuator Control Relay which powers and protects the TBW circuity. The second part of this system is the Accelerator Pedal Position (APP) assembly which transmits two pedal position inputs to the ECU. The gas pedal (APP assembly) is effectively two independent pedal position sensors which each contain a +5V reference, a ground reference, and a signal which is sent to the TBW circuitry located inside the ECU. One signal is considered the “Main” APP signal and the secondary signal is considered the “Sub” APP signal, both of which tell the ECU what the driver’s foot is doing as far as requesting torque from the motor (how much the driver is pushing down on the gas pedal).

 The next part of this system is the Electric Throttle Body Assembly which consists of the throttle actuator motor, throttle valve, and 2 throttle position sensors. Like the APP assembly this part contains 6 wires; two of which are the shared +5V reference and shared ground reference wires which power the two TPS sensors, The next two wires are the redundant TPS sensor signals (Main and Sub) which transmit the position of the throttle blade to the ECU. The last two wires are for the throttle actuator control signal, these lines control the opening and closing of  the throttle blade.

 The last part of this system is the TBW Circuitry located inside the ECU. This circuitry receives the Main and Sub APP signals so it knows what the driver’s foot is doing (as far as requesting torque) then it sends a square wave, 12 volt signal across the two throttle actuator control signal lines to step the throttle actuator motor with a duty cycle; 100% duty cycle would open the throttle blade to WOT & 0% duty cycle would keep the throttle blade at the fully closed position. Based on the feedback received from the two TPS sensor signals located in the Electric Throttle Body Assembly, the TBW system is constantly receiving inputs (APP & TPS) and controlling outputs (throttle actuator motor) in order to control the throttle blade movement on the vehicle.

drive by wire throttle body

What this means to you:

  • Most modern engines will never show a 0% TPS since the throttle blade is always kept open (by 2-7%) to start the engine and to maintain idle.
  • Some modern engines will never report a 100% TPS while at WOT since their TBW system may have been programmed to only open up to a predetermined point.
  • You can change the Rev Limits on an engine by tricking the ECU about the reported RPM but you may not be able to get the motor to accelerate past a certain RPM since the throttle body has been programmed to close by a predetermined RPM.
  • Porting of most modern throttle bodies is not a good idea unless you have the ability to fully re-calibrate that system.
  • Most modern throttle control systems to not immediately responsd to tip-out commands from the driver (letting off of the throttle) in order to optimize emissions output.

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