Please don't forget that apart from needing almost twice the energy in production (I thought carbon emissions were to be avoided) lead free PCB's generally don't survive rework/repair due to copper migration from the PCB surface to the tin. This results in more scrap/waste. Also I have read that lead doesn't leach out of solder in land fill (one of the excuses for RoHS) and there has been no noticeable increase in lead levels of people performing materials recovery (the other excuse for RoHS) That said, many of the other substances banned under RoHS legislation are a problem and the world is better without them, eg. Chromium VI and Cadmium.
It's becoming increasingly obvious that the RoHS push for lead-free solder and platings was extremely poorly thought out.
As well as the tin whisker problem, lead-free solder requires higher temperature soldering (putting more stress on components), and solder joints are much more likely to suffer mechanical fatigue.
Just another example of environmentalists creating huge problems in the "real world".
Faults like tin whiskers are exactly the reason why the pedal sensor has two pots. The values of the two pots are compared against an expected profile and if there is any discrepancy, the sensor is deemed to be faulty and power is limited to "limp home" mode.
By the way, more modern sensors use hall effect sensing which is not prone to mechanical damage like pot wipers.