Could somebody explain what functions the computer performs? So far, I've read that if you disconnect the battery, the computer will reset itself which may eliminate faulty warning lights or code displays. I also read somewhere that the computer learns driving habits(?) so resetting makes it relearn them. True? Does it somehow affect shift points for auto transmissions or how does it adapt to the driver? These are dumb questions but I didn't get the manuals when I bought my used '99 F150 and things have changed since my last Ford PU, an '85! They disconnected the battery to do my door crack repairs but I can't see any difference in driving the truck since I got it back.

 

Basically the computers in newer vehicles (OBD II) control engine and transmission functions. The computer adjusts engine timing and mixture based on sensor readings of temperature (engine coolant and outside air), RPM, load on engine, O2 level of exhaust, etc. The computer also can control automatic transmission shift points and line pressure based on similar info.

On pre OBD II vehicles the computer was controlled by a simple built in fixed program, but starting with '98 and OBD II regs things got more complex. The new computers still have a built in program of basic engine and transmission control settings, but the computers now also "learn" your driving style and make minor adjustments based on how you drive. They also can compensate for sensors that are aging and no longer are in perfect calibration. This lets the computer keep the engine in tune longer, keeping pollution down which makes the Feds happy.

But the new OBD II computers are also required, by the Feds, to watch for failed or tampered with parts like the cat converters. On older vehicles you could remove or gut the converter and no one could tell unless they looked. Do that on a new vehicle and the computer will detect it and record an error code, and turn on the dash light.

Also, the new computers have another feature that the Feds required. If something fails that does not make the vehicle run bad but does cause emissions to go up, the computer will artifically make the vehicle run bad just to force you to get it fixed. Ain't technology great?

Wait until OBD III comes along!!!!!!!!!!

Hope this poor man's explaination helps.

Take a look here for more info

http://www.obdii.com/

 

Thanks, Hawkeye, for the thorough explanation and the website referral. Great information! After reading your response and visiting the OBD site, I took a little nostalgia trip, way back to the days when I did my own tuneups using a timing light and dwell tach. Things were somewhat simpler then.
Most of the malfunctions my vehicles experience now are related to fail safe procedures, such as engine shutdowns when the oil sending unit tells the OBD there is no oil. So far, they have all been false alarms.


[This message has been edited by webfoot (edited 06-07-2001).]

 

Glad I could help. They have tried to take all the fun out of tinkering on your own vehicles, unless of course you spend a fortune on test equipment and have an Electrical Engineering degree.

I too miss the days of setting dwell with a $5 meter and timing by ear (advance it until it pings, then back it off a little).

Oh well, that's what they call progress.