Wednesday, November 30, 2011

Installing cruise control in a throttle-by-wire Toyota

Everyone remembers the uproar over electronic throttles in Toyotas. Everything from floor mats to pedal assemblies to space particles could be causing unintended acceleration. Admittedly, the last bit might just have been the NASA scientists getting bored and trying to find the problem in every last possible place. They did get into the field because they dig space stuff, after all.

At the root of the problem, it turns out, was a lot of fat, stupid feet continuously mashing on the gas pedal instead of the brake. The fact that there's no mechanical cable directly connecting the gas pedal to the throttle body had nothing to do with it, though it did give plenty of automotive Luddites a chance to bitch about technology.

Fact is, drive-by-wire throttles are handy from an engineering standpoint--no need to worry about getting the cable to reach or to work right in a certain orientation, for one. They're also handy in that some cars that don't come with cruise control can be easily retrofitted at minimal cost. Yes, I've finally reached my point.

With Zoe's 2010 Yaris, there's no computer modules to add. No expensive vacuum diaphragms or OEM switches. A trip to Radio Shack, a little time with a screwdriver, soldering iron, drill, and wire splices, and you're good to go. I'll spare you the details of the install; kind enthusiasts figured out how to do this, and posted the information online. That's how I did it. Here's the step-by-step:

More and more cars today are throttle-by-wire, so it stands to reason that methods similar to this are possible on a lot of newer cars. 

I popped off a plastic panel on the dashboard and drilled holes for these switches. After soldering in the appropriate resistor--a 660 ohm one, I think--and extra wiring, it went back into the dash. I didn't photograph it with the stuff soldered up because it's, well, not my finest work. I can solder strong, but it's not necessarily pretty.

There they are. Both are momentary pushbutton switches. Zoe calls them spaceship switches. Sometime soon they'll get labels. The top one will be Warp Drive; the bottom, Shields.

The actual in-car wiring was way easy, with just two wires to splice into.

How can you run cruise control with just two buttons? Well, it's limited in features. The top button toggles the cruise on and off (illuminating the green indicator in the top picture); the bottom one sets the speed and decelerates the car. You can wire in four switches to get full functionality, but two looks nicer and it does the job.

And it works! For less than $10 at Radio Shack, this car has cruise control. Another option for this particular car is just to install the OEM cruise control switch and cut a hole in the steering column cover for it to stick out of, but the switch—a stalk not unlike the turn signal one—is still a little pricey at about eighty bucks.

1 comment:

  1. This is fantastic. I had no idea it would be this straightforward. Great work!