Originally Posted by BigWaylon
just disconnect the battery for 10 minutes or so (to allow the capacitors to drain)...
on my Dodge Ram, we were also told to turn the key to start for 30 seconds while it was disconnected, but I'm not sure that ever made a difference...
I posted the same question on the Rubicon owners forum and got the answer I was looking for. I had seen this somewhere else and just couldn't find it again.
Greg, there seems to be a couple steps missing from the 30 seconds you were told. Maybe why it didn't make a differance.
PCM Fast Learn Mode
I think most people know that the PCM performs several functions controlling Air Fuel ratios via Injector Pulse Width and Ignition Timing.
These “outputs” are controlled using the “inputs” received from all the sensors and then comparing these reading against a set of data tables burned into the PCM.
These “memory tables” are the brains that keep the engine running at low emissions and peak economy across the RPM band
What most people don’t know is that these memory tables change. They are “adaptive”, based on sensor readings, driving habits, engine performance and sensor tolerances.
Over time, the PCM Memory Tables become tuned to your engine.
Most folks know that disconnecting the battery for 15 to 20 minutes will reset the PCM to get rid of a Check Engine Light or Error Codes stored in the PCM.
However this DOES NOT reset the Adaptive Memory Tables in the PCM. Until recently I did not know how to do this.
This procedure first came to me from the folks at Avenger. I then verified it with a phone call to a Chrysler Engineer who had called me a year or so ago to ask about my experiences with a certain part on my TJ. I figured he owned me a favor. He had to check up on this for me. He called me back a week later and did indeed verify this procedure and what it does.
To the best of my knowledge it isn’t documented in any of the FSM.
This very simple procedure will Erase the “Adaptive Memory” stored inside the TJ PCM and allow a new “Adaptive Memory” to be developed.
After performing this procedure the PCM will re-learn and store into Adaptive Memory your engines performance characteristics.
[L]Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory.
Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”[/L]
Adaptive memory has nor been flashed, or erased from the PCM.
When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory.
When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”.
The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.
A warm-up cycle happens when all of the following conditions exist.
Engine is running
A raise of 40F in engine temperature must occur ABOVE the engine temperature at start-up
Engine Coolant Temp must reach at least 160 F.
Once your engine has gone through 50 warm-up cycles in at least a 500-mile distance the PCM adaptive memory is set. It WILL NOT Change unless you flash it out and start all over again.