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Ford Electronic Throttle Control

What was wrong with a cable?

As if a simple cable linking the gas pedal to the throttle plate wasn't good enough, engineers have now made that design complicated too. Why do engineers do these things to us? That expensive throttle body can't cost less than a cheap little throttle cable, or can it? Are there any advantages to the manufacturer or the consumer with such a design? Lets examine the system and see.

In the Ford Electronic Throttle Control (ETC) system, the PCM directly controls the position of the throttle plate by use of a DC motor. A redesigned throttle body, coupled with a redesigned PCM, a redesigned throttle position sensor (the unit has 2 position sensors inside of it), and the addition of an Accelerator Pedal position Sensor (APPS) make up the ETC system directly. The ETC system replaces the throttle cable and brackets, IAC valve and its wiring, cruise control servo, plus some wiring for the cruise system as well. The only part of the ETC system that is truly new (excluding redesigning) to the gasoline vehicle is the APPS, and it has been in service on the DI diesel for years. So with that considered, what appears to be more complicated on the surface, is actually less elaborate when viewing the entire scope. It might cost less to build, too.

The principle reason for using the ETC system is for improved driveability through its torque based strategies, which take better advantage of Variable Cam Timing (VCT) and transmission shift strategies. There are however, other benefits. It allows the PCM to limit vehicle speed and engine rev through throttle control, rather than inducing misfires. Also, adding factory cruise control to a vehicle that wasn't originally equipped with cruise becomes a snap; Simply replace the steering wheel (in some cases replace the clock spring too) and tell the PCM it has cruise with a capable scan tool. Nice huh?

The ETC system also helps pave the way for future design changes to the vehicle's passenger compartment as well; such as the consumer being able to slide the vehicle controls to the opposite side of the dash. ETC also makes it possible for the traditional throttle pedal to be eliminated all together by replacing it with hand controls on the steering wheel. That feature holds obvious potential for dealer- or factory-equipped handicap driver applications.

Now that we have talked about the names of the parts, lets see how they operate.

Ford ETC Theory and Operation

Based on the APPS input, the PCM changes the angle of the throttle plate by directly actuating the DC motor mounted to the throttle body assembly. The TPS, mounted on the throttle body, provides feedback to the PCM of the throttle plate position. The purpose of the TPS has been modified in the ETC system from that of the cable type system. Rather than being the source of driver throttle demand information, the TPS is now simply for the PCM to be able to monitor its own actions with the throttle plate. The APPS sensor is now what represents the drivers throttle demand, which is something to keep in mind when reviewing fault code freeze frame data.

The APPS

The Accelerator Pedal Position Sensor (APPS) mounts to the top of the throttle pedal. Inside of it are three position sensors and two return springs. The position sensors send an analog DC signal to the PCM, as you can see below.

The PCM uses APPS1 as the primary indicator of the driver's throttle demand. APPS1 uses a negative slope. In the at-rest position, APPS1s voltage is high, usually starting around 4.0 volts. As the pedal is depressed, ...

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