Electronic Throttle Control System: Prius

Electronic Throttle Control System (ETCS) consists of throttle body, accelerator pedal position sensor, Throttle Position (TP) sensor, throttle control motor, Hybrid Vehicle (HV) control Electronic Control Unit (ECU) and Engine Control Module (ECM). Hybrid vehicle control ECU is referred to as HV ECU. ETCS uses ECM to calculate throttle valve opening in the throttle body in relation to driving conditions. ETCS controls idle speed and cruise control system operation. Accelerator pedal position sensor is mounted near accelerator pedal. See Fig 1. Accelerator pedal position sensor consists of 2 internal sensors which deliver accelerator pedal position input signals to the HV ECU. HV ECU in turn delivers the input signals to ECM. TP sensor delivers input signals to ECM to indicate throttle valve opening.

ECM uses input signals to operate throttle control motor to obtain proper idle speed and provide cruise control operation. Throttle control motor is mounted on side of throttle body and operates throttle valve. See Fig 1.

In the event of an ETCS malfunction, Malfunction Indicator Light (MIL) will be illuminated and Diagnostic Trouble Code (DTC) will be stored in ECM. MIL is displayed as an engine icon on instrument cluster at center of instrument panel. See TESTING PROCEDURE under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article for retrieval of DTCs. If malfunction exists, voltage to throttle control motor is turned off in which throttle control motor becomes inoperative, allowing spring pressure to close the throttle valve.

Fig 1: Locating Electronic Throttle Control System Components On Throttle Body & Accelerator Pedal Position Sensor (Prius)

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