Topic: Please check this over

[grumpygy]

Got this from Quadretec.  Not sure of the years it covers.

When installing new power or performance accessories how does the computer for the Jeep know that it has a new accessory?  Most of the time the computer does not.  The computer would need to be reset to take full potential of the performance accessories you have added. 

The Electronic Control Module, or ECU as its commonly called, stores the information for your vehicle and your driving habits in its memory.  The memory is maintaned by a series of capacitors that hold a charge and maintain power for the ECU when the vehicle is turned off.  The following procedure will allow you to reset the memory and allow the computer to 're-learn' how to drive by adjusting to the drivers habits and the vehicles modifications. 



1. Disconnect the battery by removing the positive battery cable. Remember, the positive battery cable.

2. Ground the positive cable to the negative cable for 30 seconds to erase the electric charge in the capacitors.

3. Reconnect the positive cable to the battery.

4. Turn the key to on but do not start.

5. Turn the headlights on.

6. Turn the headlights off.

7. Turn the key off.


The ECU has now been reset to its factory settings. For the next 50 warm-up periods the ECU will re-learn the engine and driving habits for your driving conditions and the newly installed parts. 

[jfrabat]

I had never heard of the light part before, but on YJ's, simply connecting the positive to the negative terminal for 30 secs will do the trick.

[sharpxmen]

I had never heard of the light part before, but on YJ's, simply connecting the positive to the negative terminal for 30 secs will do the trick.

it's the way to reset the 'puter for TJ

[grumpygy]

it's the way to reset the 'puter for TJ

The lights was the 1st I heard thats why I asked.

[Jeffy]

The light part is to make sure the caps have drained completely.  It's probably not necessary but then I usually ground my cable for more then 30 seconds.

[sharpxmen]

The light part is to make sure the caps have drained completely.  It's probably not necessary but then I usually ground my cable for more then 30 seconds.

you do that with the battery connected so i don't think it's for the caps

i've seen the same sequence somewhere else for TJ, could be something that is built into the PCM to erease the memory or codes, dunno for sure just guessing

[knotts89]

Just checking here, but do you take the positive terminal and put It on the negative post for 30 seconds and are you supposed to take the negative off beforehand? Sorry for the newbie question just never heard of doing this thanks guys

[sharpxmen]

Just checking here, but do you take the positive terminal and put It on the negative post for 30 seconds and are you supposed to take the negative off beforehand? Sorry for the newbie question just never heard of doing this thanks guys

you don't have to disconnect the negative (ground) as long as you disconnect the positive from the battery

[knotts89]

Then you just hold it to the negative post

[grumpygy]

You won't get a short cause the Positive is not connected to the battery,  Just use care when taking the positive off.  That is why normally you take the negative off 1st.

[Bounty Hunter]

I've heard of the headlight step before, but it was while the positive cable was grounded to the neg side.  This puts a load on the caps instead of the battery and ensures they discharge.  Makes no sense to me why you would turn the headlights on once connected back to the battery.

[grumpygy]

Found this for the reason why.

CM 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.



Forced Flash

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.


Warm-up Cycle

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.

[grumpygy]

Found several places that say this is good for all to include YJ.

[neale_rs]

Very interesting find.