Proper way to reset the PCM

Farmer Fran · Nov 12, 2013

What is it? tia. :happy160:

Farmer Fran · Nov 12, 2013

I guess technically it is the ECM

Texas_Cornhusker · Nov 12, 2013

Farmer Fran said:
What is it? tia.

remove + side of battery, wait 15min, put back on. done

dodge dude94 · Nov 12, 2013

You should turn the headlights on after you do that aswell, before the cable goes back on.

DanielSix26 · Nov 12, 2013

I suppose this is a good place to ask-

What are the reasons I would want to do this? I have a vague idea but...

Farmer Fran · Nov 13, 2013

I want to reset my fuel maps. I was running 87 in my truck. Switched to 89 and lost 3-4 mpg.

No I did not buy the truck for the MPG but 3-4 is significant enough to catch my attention. So I figue this is an easy check. Yes, there could be many other reasons but I want to put this to rest.

LETHAL GTS · Nov 13, 2013

dodge dude94 said:
You should turn the headlights on after you do that aswell, before the cable goes back on.

Ok I'll bite.
Why?

Coop · Nov 13, 2013

Farmer Fran said:
I want to reset my fuel maps. I was running 87 in my truck. Switched to 89 and lost 3-4 mpg.

No I did not buy the truck for the MPG but 3-4 is significant enough to catch my attention. So I figue this is an easy check. Yes, there could be many other reasons but I want to put this to rest.

That sounds like the winter fuel switch to me. Maybe combined with ethanol in the 89 you're using? E-10 has about 3% less energy per gallon than straight gas. Winter blend has less energy as well, and a higher evaporation rate. Loss of MPG with winter blend is also compounded when the outside temp is higher.

It's fine to reset, but if I had to bet it would be those factors and not the octane rating.

HolyRamBatman · Nov 13, 2013

LETHAL GTS said:
Ok I'll bite.
Why?

It's suppose to help drain all power from anywhere it can find it. I.E. capacitors.

It's possible.....

Farmer Fran · Jan 27, 2014

Well decided to wait to see if the ECM would relearn on its own but nope...

My exhaust pipes are black, truck is running way too rich! Cannot believe it is the winter gas either. Gonna try to reset it now.

JohnD72 · Jan 27, 2014

For safety's sake, it is generally recommended to disconnect the negative terminal before the positive. This reduces the risk of touching a ground while working with the positive terminal - and making bad stuff happen.
The result will be the same.

Farmer Fran · Jan 29, 2014

Wouldn't disconnecting the negative give the same result either way?

No path is no path.

JohnD72 · Jan 30, 2014

That's what I meant by "the result will be the same."

mesaboogie · Jan 30, 2014

Octane rating is the resistance to burn so it doesn't combust before the spark due to the compression. You won't get 3-4 mpgs from this when the engine is able to run both 87 and 89 just fine.
The fuel trim is a constantly evolving system, and with all the electronics available now to cut cylinders and even completely cut fuel when coasting, any minor change in driving can have a huge effect that adds up quickly to boosting or cutting mpg.

As for the battery, remove the negative first and connect it last.

Proper way to reset the PCM

Farmer Fran

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