Is EOC giving my ECU Alzheimer's?

[Bearleener]

Are frequent engine starts causing problems with my car's anti-theft system?

I've been happily doing Engine-Off-Coasting (EOC) and engine off at stoplights for about 3 years now without any noticeable problems, but I've had one problem with my car that's happened 3 times in the last 2 years:
The electronic anti-theft system (immobilizer) has konked out, which means I couldn't start the car, had to have it towed to the shop. It's only happened when the car had been parked, so far never on the road.
This system uses an inductive coil to read a code number from the ignition key, and a nearby control unit sends that code to the ECU; if the number from the control unit doesn't match that stored in the ECU then the engine won't start.
The first time they replaced the inductive read coil (a known occasional problem in VW's). The second time (6 months later) they replaced the control unit. And recently (another 18 months later) the diagnostic computer said that the ECU had forgotten the code, so they reprogrammed that.

Now I'm beginning to wonder if my frequent starts (about 10 times as often as "normal" people would do on my route) may be causing this. Wouldn't know why, though. I wouldn't expect something like EPROM write cycles being exceeded.

Have any of you guys had similar problems?

[Clev]

Are you killing the ignition switch or a sensor like the crankshaft position sensor to achieve EOC? I haven't installed a kill switch yet specifically because I want a way to do it without removing and reapplying power to the ECU at every stoplight.

[Bearleener]

I've got a button that interrupts the Hall sensor signal at the distributor (on mine it's a green-and-yellow wire, as I recall), so the ECU and everything stays on all the time (didn't want to lose airbags or odometer either).

I restart either by bump starting or with another button that runs the starter over a relay. But the ECU will certainly query the anti-theft system's key code every time regardless, because otherwise thieves could just push-start the car.

[wagonman76]

Sometimes at a long stoplight or when I see a long line of cars at a stop sign, I shut off the engine. If I take off too quick after starting it, the Check Engine light stays on for about 5-10 seconds.

Also, if I've been running light load and low rpm for a long trip, the car does not want to idle right when starting back up, and sometimes stalls out.

[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!