[Bearleener]

Update: It happened again! The ECU again forgot the authorized ignition key code number and refused to start the engine (electronic anti-theft immobilizer). So I had to tow the car to the dealer again, for the 4th time! They replaced the control unit for the key reader coil, but that probably wasn't the problem.

The consequence for me is no more EOC (engine-off coasting) :-( sniff!
I'm very disappointed because this technique was saving me at least 5% in fuel consumption. My engine was usually off for about 8-9 minutes of my 30-minute commute. If I now can only key off at stoplights that's only about 3 minutes.

My theory about what is happening: I kill the engine with a momentary switch that interrupts the signal from the Hall sensor on the distributor. Every time I do this the ECU (engine control unit) "throws a code", i.e. writes an error flag in its memory (indeed the ECU error log read out by the dealer showed a "no signal from Hall sensor" error). I did this about 10 times per commute, i.e. 20 times a day or roughy 4400 times a year. Somewhere I read that an EEPROM is only good for about 10,000 erase/write cycles before it starts becoming error-prone. In my case that would be after about 2.3 years; yep, that's about right. Presumably it's starting to botch the error write operation, erasing the immobilizer's key authorization code number in the process.

So it's back to using the ingition key to turn the engine off, but I don't like to do this when rolling because I have a couple seconds of blackout without airbag or odometer; not good.

Moral of the story: If you're using ecomods or driving techniques that cause your ECU to throw codes, you may be causing your ECU to get premature Alzheimer's!