I've read a couple of posts where people did some repairs and reset the computer upon completion. What does this actually do for your truck? How would you go about doing it.
As long as I'm tearing into my engine anyway, might as well replace the various input sensors for speed density and reset the computer!

'95 F150, 351, E4OD, 4x4

 

Disconnect the negative battery cable and leave it disconnected for at least 30 minutes.

This erases all the memory in the computor and forces it to relearn what is "normal" for all of it's various inputs and what not. Since not all sensors are created equal, it is a good idea to do this when replacing sensors.

 

Right on, eco. Thanks for the quick post. This forum is the best I've been a part of, truly an invaluable resource to home mechanics!

 

Just thought I'd add when the computer is disconnected the engine will need to relearn its idle. After reconnecting the battery start the truck and let it idle for a minute, it may idle a little shaky at first but it will sort its self out.

If you were to just hop in the truck and drive off it would take a little while for it to relearn its idle again.

 

Another reason for knowing how to do this:
My truck occasionally has the check engine light come on, and throws a code for the EGR. CA emissions test will fail me automatically if it reads the stored code.

Twice in the last 4 years before getting tested, I disconnect the battery and clear the codes, and she passes no problem. This last time, the CEL came on again on the way home from the test.

I suppose one of these days I oughtta get under the hood for real...

 

you can clear the codes by just reading them. you don't have to disconnect the battery.

 

The best way I've found to erase the memory codes is to pull the jumper in the middle of the tests. This immediately halts the test and resets the constant memory to 1-1-1 again. You don't have to wait 30 minutes that way.

 

Maybe so, but there is a difference between 1) Trying to get rid of the stored codes in the computer and 2) Forcing the computer to re-learn what is normal for all of the sensors so that the computer is able to properly run the engine after different parts of the engine management system have been replaced with new parts. The thread starter is trying to do the latter.

 

eco, are you saying that the battery disconnect method erases all memory, and the jumper only erases stored codes ??

That's good to know.

 

Yes............

 

I guess I was under the impression he just wanted to clear them to pass his test, But yes if a new part is installed then it is a good idea to unhook the battery and do a total reset.

 

Just two things to add - there is virtually nothing to gain by replacing SD sensors just because you're in there. If they're good, they're good. Given the quality of some aftermarket parts, you are better off leaving a working sensor in place.

Secondly, reading the codes from an OBD-I computer doesn't reset them. Whoever posted that is thinking of OBD-II.