Post by wv4x4 on Apr 10, 2006 13:11:29 GMT -5
Since this was being discussed in another thread I figured I would post it here. I do this about twice a year!
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.
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 not 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.
A battery disconnect will reset the minimum throttle (TPS) angle strored in PCM memory. The PCM learns the closed throttle angle to calculate load. A battery disconnect will reset this value to the factory programmed value for closed throttle, and the actual value if different will be relearned when the vehicle is driven.
A battery disconnect also clears adaptive fuel. This is a two step program, the PCM storing both long term and short term adaptive "numerators" for the fuel required to achieve the desired air/fuel ratio. For example, if the fuel pump is aging and becoming weak, the PCM can increse fuel injector "on-time" to compensate. If it sees it needs to do this a lot, it adds numbers (in percent) to the long term fuel "trim". This percent is then added to the PCM's calculations and monitored again. While this value doesn't actually add anything, it serves to get the computer to the "ideal" that much faster. A battery disconnect will require the PCM to relearn these values, and is VERY intensive
(there are separate values stored in every RPM/load possibility)
A battery disconnect also resets the IAC (idle air control) value to the preprogrammed value. The PCM learns the IAC duty cycle to maintain closed idle without flare or stall, and uses this value for subsequent styarts. A battery disconnect resets this value to a value that USUALLY results in a low idle or stalling condition at idle until this value is relearned.
A battery disconnect will reset CVI's (clutch volume index) for automatic transmissions. The CVI is a compensator, and the PCM "knows" how long shifts take to complete from the time they're commanded. The difference in time between command and completion is stored in the PCM and is used to alter command time to achieve the actual desired completion time of the shift. A CVI value is stored and retained for each gear. A battery disconnect will reset these values to zero again, and shifts will be notably different (generally sooner and harder) until the PCM relearns the delay times.
A battery disconnect will reset the learned crank/cam sensor synchronization. Both of these sensors have a "signature" that the PCM uses to determine the activity and relative position of the cam, crank, or both. There is almost always a slight asynchronous delay between the reference points on these two sensors, and the PCM learns this misalignment and comensates for it. A battery disconnect will reset this value to result in no compensation and fuel injection timing will be off (not ignition timing) until the misalignment is relearned or manually corrected at the cam sensor housing adjustment provision.
A battery disconnect will also clear all stored trouble codes (DTC's) but will NOT clear active codes. Active codes must be corrected before clearing. When DTC's are cleared from memory by a battery disconnect, very important data is also lost. At the time the code was set, the PCM takes a "snapshot" of all the pertinent computer data and stores it in memory (freezeframe) for diagnostic purposes. This information is often extremely useful in diagnosing and correcting trouble code related problems, so it's best to NOT disconnect the battery to clear codes UNLESS you feel you've made a repair that may keep the light out.
A battery disconnect will also clear "pending codes" which are trouble codes that met all the criteria to set the light, and will do so the next time the fault occurs (called 2 trip codes)
A battery disconnect will also clear the OBDII readiness monitors. This is important to note, since many states now use OBDII scanning devices to serve as the equivalent of the emissions portion of the inspection program. The readiness monitors are tests that are run and the results recorded in "complete/not complete" format in the PCM Once these monitors are cleared, it may take up to a week to run them all to provide enough data to perform an OBDII smog check
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.
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 not 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.
A battery disconnect will reset the minimum throttle (TPS) angle strored in PCM memory. The PCM learns the closed throttle angle to calculate load. A battery disconnect will reset this value to the factory programmed value for closed throttle, and the actual value if different will be relearned when the vehicle is driven.
A battery disconnect also clears adaptive fuel. This is a two step program, the PCM storing both long term and short term adaptive "numerators" for the fuel required to achieve the desired air/fuel ratio. For example, if the fuel pump is aging and becoming weak, the PCM can increse fuel injector "on-time" to compensate. If it sees it needs to do this a lot, it adds numbers (in percent) to the long term fuel "trim". This percent is then added to the PCM's calculations and monitored again. While this value doesn't actually add anything, it serves to get the computer to the "ideal" that much faster. A battery disconnect will require the PCM to relearn these values, and is VERY intensive
(there are separate values stored in every RPM/load possibility)
A battery disconnect also resets the IAC (idle air control) value to the preprogrammed value. The PCM learns the IAC duty cycle to maintain closed idle without flare or stall, and uses this value for subsequent styarts. A battery disconnect resets this value to a value that USUALLY results in a low idle or stalling condition at idle until this value is relearned.
A battery disconnect will reset CVI's (clutch volume index) for automatic transmissions. The CVI is a compensator, and the PCM "knows" how long shifts take to complete from the time they're commanded. The difference in time between command and completion is stored in the PCM and is used to alter command time to achieve the actual desired completion time of the shift. A CVI value is stored and retained for each gear. A battery disconnect will reset these values to zero again, and shifts will be notably different (generally sooner and harder) until the PCM relearns the delay times.
A battery disconnect will reset the learned crank/cam sensor synchronization. Both of these sensors have a "signature" that the PCM uses to determine the activity and relative position of the cam, crank, or both. There is almost always a slight asynchronous delay between the reference points on these two sensors, and the PCM learns this misalignment and comensates for it. A battery disconnect will reset this value to result in no compensation and fuel injection timing will be off (not ignition timing) until the misalignment is relearned or manually corrected at the cam sensor housing adjustment provision.
A battery disconnect will also clear all stored trouble codes (DTC's) but will NOT clear active codes. Active codes must be corrected before clearing. When DTC's are cleared from memory by a battery disconnect, very important data is also lost. At the time the code was set, the PCM takes a "snapshot" of all the pertinent computer data and stores it in memory (freezeframe) for diagnostic purposes. This information is often extremely useful in diagnosing and correcting trouble code related problems, so it's best to NOT disconnect the battery to clear codes UNLESS you feel you've made a repair that may keep the light out.
A battery disconnect will also clear "pending codes" which are trouble codes that met all the criteria to set the light, and will do so the next time the fault occurs (called 2 trip codes)
A battery disconnect will also clear the OBDII readiness monitors. This is important to note, since many states now use OBDII scanning devices to serve as the equivalent of the emissions portion of the inspection program. The readiness monitors are tests that are run and the results recorded in "complete/not complete" format in the PCM Once these monitors are cleared, it may take up to a week to run them all to provide enough data to perform an OBDII smog check
