P3191, huh?

Two nearly identical posts about "P3191 Engine does [rjw] not Start" DI-158, got me wondering:

So I went back to Volume 1 of the Prius Shop Manual:

From the HV ECU, the ECM receives data such as power output required for the engine (required output)., estimated torque produced by the engine (estimated torque), engine RPM of control target (target RPM), whether the engine is in start mode or not. Then, based on the required output and target RPM, the ECM calculates a target torque that is to be produced by the engine and compares it with the estimated torque. If the estimated torque is low compared with the target torque, or the engine start mode continues at the engine RPM or for the duration calculated by water temperature, an abnormal condition is detected.​

The trouble area:

• Air induction system
• Throttle body
• Fuel pressure
• Engine
• Air flow meter
• Out of fuel
• Water temp. sensor
• Crankshaft position sensor
• Camshaft position sensor
• ECM

I think what we have is misdirection around "Out of fuel." The reason is I have run our 2003 Prius out of gas over 40 times as part of fuel and efficiency studies. But in my case, I simply drove to a safe place to add 1 gallon and the car started right up. But we know from other out of gas events that if the owner tries to restart the car three times, it sets another code/latch that prevents further attempts to turn over the engine and drain the traction battery.

The field method to get an 'out of gas' Prius to run when the owner already tried three times, is add gasoline and disconnect the 12v battery to reset all codes and the latch that prevents restart. At least 3 gallons are needed to turn off the low-fuel, flash, but I always used a 1 gallon can and never worried about disabling the low fuel level "flash."

When I run out of gas, the car is typically, well warmed up and adding one gallon provides ~52+ miles before it is gone. So I simply drive to a gas station and fill-up. That clears the "flash" and the fuel sensor has nothing to do with it.

This strange description of P3191 makes sense from an out-of-order, set of data points associated with running out of gas and they did not realize:

• 3 start attempt limit - requires disconnecting 12V to reset codes 'in the field'
• low fuel 'flash' requires ~3 gallons to turn off this cosmetic effect

Now I'm down to 3-bars in the 2003 Prius as I get ready for a 'driving stunt.' I've never deliberately done the "three restart" lockout test. But I do have a mini-scanner and wrenches to disconnect the 12V ground. I would like to understand what is set on the lock-out start attempts.

Bob Wilson