CNN Video - Experts say problem is electronic interference - not hardware or floor mats

I'm sure youv'e heard: ex-perts are "Drips that have been spurts under pressure"

 

It's clearly the bluetooth floor mats that are creating the electrical interference.

 

The accelerator pedal position sensors in Gen 2 and Gen 3 Prius are Hall-effect electromagnetic sensors. It's just possible that an electromagnetic field could alter the output of those sensors, though I would expect it to be in a way that would show up in the rationality of the sensor outputs (they're supposed to track each other, a fixed voltage apart).

I suspect these 'experts' have not taken a single look at the car's service manual, which explains - to a degree - how these systems work.

The pedal position sensors in the conventional, non-hybrid, cars appear to be twin potentiometers as in Gen 1 Prius - the part that caused the 'big hand' syndrome. The throttle position sensors - which report where the throttle blade actually is - are still potentiometers in the later Prius models.

An issue that I don't think enough attention is paid to is the influence of ground loops in the circuits, as the car's chassis is used as a common ground, with many different points of connection. In the case of the accelerator pedal position sensor on the Prius, ground connections are made directly with the HV ECU, not with a separate ground point, although the ECU's ground connections are made to a different point from the shielding surrounding the wiring from accelerator to ECU. Similarly the throttle position sensor's ground connection is made directly to the ECU, but in this case the shielding is connected to the same ground point as at least some of the ground connections on the ECU.

I believe the throttle motor is analogue, not a stepper. It has two connections to the ECU marked M+ and M-. To hold position, it supplies just enough current to balance the force of the return spring. A little less causes the blade to move back toward the spring's rest point, a little more causes it to move away. The return spring does not fully close the throttle blade, in case electronic control fails - in this situation the ECU controls power through fuel and spark timing alone, at the cost of poor fuel mixtures (excess emissions). To fully close the throttle the ECU drives the motor in the other direction.

Hobbit has done a tear-down of a failed (or at least replaced) throttle body assembly.

 

Mike, thanks for the explanations and the reference to Hobbit's throttle tear-down, with the excellent illustrations of the details of the throttle body assembly.

Interesting to note that the return spring is a dual concentric unit, hence doubly redundant. Although I would guess that the probability of one of those return springs failing is less than the probability of being struck by lightning.

I guess my reference to a stepper motor was technically incorrect; what I had in mind was a motor similar to the servo motors contained in the servos I used during the time I was flying RC sailplanes. There were 6 used in the so-called "full house" sailplanes, used to position the flaps, ailerons, rudder and elevator. These received PWM signals from the on-board receiver, via the hand-held transmitter. Naturally, being signaled over the air, potential interference from extraneous sources of frequency harmonics is always present; all you have to do is look at the FCC and NTIA radio spectrum allocation chart to realize how surrounded we are by electromagnetic emissions. These are strictly controlled by the FCC with respect to signal strength of course, but that doesn't stop people from violating the restrictions.

All of that said though, I am sure Toyota has done the necessary tests to ensure the required shielding is in place for their control setup. Not being an expert in this field, I defer to the superior knowledge of those that are.

I continue to maintain that the greatest threat to life and limb when driving is the integrated software package sitting behind the steering wheel. Well developed perhaps, but still the product of unskilled labor!