Why do car computers fail?

[vancouverbc]

I took my 1991 240sx to mechanic and they are telling me I need a new computer. I did notice that when I disconnected O2 sensor I was not getting an error code for O2 sensor. Sometimes I would get the error code for injector leak instead.

The thing is that self-diagnostics said the fuel mix was right ie blinking check engine light. I did a voltage test on O2 sensor with it hooked up to ecu and voltage was going .2,.3,.4,.6,.8 volts which suggested the ecu was controlling the mix

My other codes worked and my engine seems to run and idle fine.

[Florida240sx]

What made you bring the car into the mech? ECU's can be bought for under $75 shipped...ECU's go bad because they don't have windows XP..... Usually a short in the system outside the ECU.

[vancouverbc]

Interesting, thanks. Do you get computers from private sales or is there a company selling the ecu's?

I was failing emissions. The short thing worries me because it might happen again. I did cut my O2 sensor wire a couple years ago and mended it back together. Just ominous that only my O2 is not producing codes.
Modified by vancouverbc at 5:27 PM 1/3/2007