How Electronic Throttle Control (ETC) Works

typical electronic throttle body with stepper motors and throttle position sensor
A Typical Electronic Throttle Body – Look Ma, No Cables!.

The internal combustion engine (ICE) of your car is essentially an air pump, pulling in air through the intake system and expelling it through the exhaust system. Engine power output is determined by intake air quantity, controlled by the throttle body. Until the late 1980s, the throttle body was controlled by a cable, connected directly to the accelerator pedal, which put the driver in direct control of engine speed and power. Cruise control systems, too, were connected via cable to the throttle body, controlling engine speed with an electronic or vacuum motor. In 1988, the first “drive-by-wire” electronic throttle control (ECT) system appeared. The BMW 7 Series was the first to feature an electronic throttle body (ETB).

Electronic Throttle Control Components

Cross-Sectional Diagram of Electronic Throttle Body
No Cables Drive the Electronic Throttle Body, but an Electronic Stepper Motor and Gears (Green).

The electronic throttle control system includes the accelerator pedal, ETC module, and throttle body. The accelerator pedal looks the same as it always has, but its interaction with the throttle body has changed. The throttle cable has been replaced by the accelerator position sensor (APS), which detects the exact position of the pedal at any given moment, transmitting this signal to the ETC module.

When electronic throttle control first appeared, it was accompanied by its own ETC module. Practically all modern vehicles have integrated electronic throttle control into the engine control modules (ECM), simplifying installation, programming, and diagnosis.

An electronic throttle body looks like a typical throttle body. It is fitted with an electronic servomotor or stepper motor and a throttle position sensor (TPS) instead of cables. Real-time TPS data confirms actual throttle position for the ETC module.

How Electronic Throttle Control Works

instrument cluster tachometer, engine rpm
Accelerator Pedal Actually has Less Effect on Engine Speed than Most Think.

At its simplest, the ETC module reads input from the APS and transmits servomotor instructions to the throttle body. Basically, when the driver depresses the accelerator 25%, the ETC opens the ETB to 25%, and when the driver releases the accelerator, ETC closes the ETB. Today, electronic throttle control function is more complex and functional, with several benefits to such ETC integration and programming.

  • Idle Air Control: Engine idle speed needs to be adjusted to account for engine load and temperature. Some vehicles with ETC don’t use an idle air control (IAC) valve or idle-up vacuum switch, but control engine idle speed using the ETB.
  • Cruise Control: Modern electronic throttle control systems control vehicle speed electronically, with additional programming inputs from VSS (vehicle speed sensor), shift position, and set speed. Adaptive cruise control adds additional sensor inputs, such as from RADAR, LIDAR, or SONAR systems.
  • Traction Control: Using other sensor inputs, such as VSS, individual WSS (wheel speed sensor), and shift position, ETC can modulate engine output to reduce wheel spin, such as when accelerating on low-traction surfaces, such as snow, ice, or gravel.
  • Electronic Stability Control: At higher speeds, by monitoring VSS, WSS, g-force, and yaw rate sensors, ETC can modulate engine power output to improve vehicle stability.
  • Pre-Collision Systems: Using input from the pre-collision system (PCS), electronic throttle control can cut engine power in case a crash is calculated to be unavoidable.
  • Transmission RPM Management: On some vehicles with sport transmissions, ETC can use engine speed (RPM), shift position, VSS, and other sensors to match engine speed to the intended gear selection. In a manual transmission, this would normally be modulated by the driver, such as punching the accelerator during a downshift, but in an ETC vehicle, “throttle blips” are perfectly synched with downshifts for faster engagement and smooth power transfer.

Typical Electronic Throttle Control Problems

Check Engine Light in Modern Automobile
Check Engine Light Could Indicate an Electronic Throttle Control Problem.

Electronic throttle control is more complex and more expensive than old cable-driven systems, but it tends to last longer—at least a decade. Still, there are a few symptoms that could indicate a problem in the ETC system.

Some resistor-based APS and TPS can wear out over time, leading to “blank spots” in the signal, where resistance or voltage suddenly spike or drop. Of course, ETC programming sees these spots as a malfunction, putting the whole system into failure mode. If restarting the vehicle seems to “fix” the problem, it might be related to an APS or TPS intermittent failure. Loose wires or connectors, too, could simulate this kind of problem.

If the check engine light comes on, there are several ETC-related codes that address the system. In this case, the vehicle may seem to be “running fine,” in which case the failure is likely a backup circuit – some ETC systems use parallel APS and TPS circuits for self-testing and failure redundancy, so you can still drive around. In some cases, you may experience limited engine power or vehicle speed, in which case the ETC has gone into a limited-operation failure mode.

As a DIYer, you may be able to check wires, connectors, and sensor voltage, but anything deeper may have to be left to the professionals. Any voltage checks should only be done with a high-impedance DMM (digital multimeter), to prevent possible damage to sensitive electronics.

Is Electronic Throttle Control Safe?

Modern Automobile Repair Technicians Diagnose and Program Vehicles
Hundreds of Thousands of Electronic Throttle Control Lines Proven Safe.

One can hardly mention ETC without mentioning the Toyota UA (unintended acceleration) Recalls, which affected some 9 million vehicles around the world. Supposedly, ETC malfunctions caused vehicles to suddenly accelerate out of control. Legal investigators claim to have discovered over 2,000 UA cases, causing uncounted crashes, hundreds of injuries, and nearly 20 deaths, further claiming these were caused by malfunctions in Toyota’s ETC system.

Still, deeper investigation, by the NHTSA and NASA (National Highway Traffic Safety Administration and National Aeronautics and Space Administration), discovered no faults in any of the vehicles. Both of those investigations revealed these crashes to be caused by pedal misapplication or entrapped floor mats.

In any case, Toyota went on to improve standards for floor mat installation and accelerator pedal shape, as well as to add brake-throttle override (BTO) programming, which cuts engine power in case brake and accelerator pedals are depressed simultaneously. This is similar to a system that some other automakers have already implemented in their own ETC systems, and is mandatory on all ETC-equipped vehicles, that is, almost every single vehicle available since 2012.