Toyota ETCS-i is Expo!

One of the upsides to older car ownership is that over time, more internal information tends to leak out from manufacturers.

Every vehicle has a relationship between pedal input and throttle. With older vehicles, there was a lever, linkages, or cables between the pedal and engine. Some amount of nonlinearity can be chosen by adjusting the linkages or the throttle pulley. With electronic systems, we can replace that relationship with software, and switch it at runtime.

Toyota's implementation is known as Electronic Throttle Control System- intelligence(or ECTS-i), and I recently found a "How it works" PDF. Largely the 2000s can be divided into three periods for each Toyota model: before ETCS-i(mechanical throttle cable and pulley), ETCS-i with mechanical fallback, all-electric ETCS-i.

At time of writing, I still own a 2002 Toyota Highlander. There's a throttle cable between the pedal and throttle, so I knew it wasn't not fully electric. This car features a Snow-Mode button that tends to reduce take-off burnouts, but I have always wondered exactly how it works. This PDF confirms that snow mode does nothing at all to the throttle - Highlanders up to 2003 are mechanical cable only, and 2004 and beyond are ETCS-i. This largely confirms that snow-mode on these earlier 1st gen cars is implemented by adjusting the transmission shift points.

Later on in the document, there's an interesting description of the details of the newer implementations. To start, the pedal is a 5v sensor, and outputs a linearized DC voltage(presumably with the standard headroom & footroom that allows the ECU to detect a broken or shorted signal wire). Once the ECU reads the input from the pedal, it can remap the pedal to throttle relationship programmatically, like so:

Anyone who has tuned RC vehicles may recognize these curves as...mostly just expo!