Well, you have to remember that the ECU needs inputs to control ignition timing. Inputs to the ECU include crankshaft position, and camshaft position sensors (to name just two). Some engines require cam and crank sensor inputs to run; the 1503 only needs the crankshaft position, but if the signal is missing or erratic, it will prevent proper ignition timing.
Here's an example of a faulty crankshaft position sensor signal on a 2017 GTR 230; the engine ran, but it ran like crap ... like it was misfiring.
Here's the signal after the sensor was replaced. Notice the slope rising at the gap in the reluctor wheel. Now go back to the previous picture and look at the falling slope. See the difference?
Typically, once ignition coil driver in the ECU is fried, it's fried for good ... they don't heal themselves. On the crankshaft sensor, I've seen these sensors produce signals that "come and go" especially when they get hot ... when they start to fault, they do so when they get hot.
The problem with the older 2002 engine is the crank sensor requires you to pull the PTO cover, so that means an engine pull. On new engines the sensor can be removed without pulling the PTO cover.
One last thought, the BRP instructions for testing the crankshaft position sensor are woefully inadequate! In the BRP version, you use a multi-meter, but a multi-meter isn't fast enough to see the whole wave form; without the wave form, it's impossible to properly analyze the signal.
