Any benefit to resetting PCM?

I just had a positive experience with resetting the PCM's adaptive numerator using the instructions from @Wombat

I had recently replaced the OPDA and camshaft position sensor due to a P1391 CEL at high RPMs (there was excessive, lateral play in the OPDA that caused the sensor ring to wobble at high RPMs which damaged the camshaft position sensor).

Soon after, I began getting a new CEL for random misfire (P0300) together with a couple of cylinders (P0304 and P0306), but only at high RPMs.

I had recently replaced my spark plugs with a model recommended here, and I felt like the engine was running fine (sounded smooth with no signs of misfiring, etc.). I double-checked those spark plugs for gap, etc., but still got the codes. I decided to try the reset to force the PCM to relearn from scratch, and the misfire codes went away. I have test-driven it several times at high RPMs and the PCM no longer sets any CELs.
 
1RAD said:
Any alleged actions beyond disconnecting the battery for a few minutes is a myth.
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Turning the lights on and off is simply an extra step to ensure any capacitor holding a charge is disposed of that can - although according to some I've apparently been completely mislead to believe - maintain the adaptive memory.

It can take longer than just a few minutes to discharge all the capacitance within the PCM and that's why the directions state "Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds" because it works and furthermore - in theory - instantly discharges any stored charge within the electrical system, 30 seconds makes sure.

The directions are as such to be 100% sure of doing the job and it cost you nothing to go through the process, so that's nice :)

RMETeeJay said:
I just had a positive experience with resetting the PCM's adaptive numerator using the instructions from @Wombat
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Nothing like a free fix
 
Wombat said:
I think it's a good thing to reset the PCM every other year or when you replace sensors, regear, or change what fuel octane you use.

I reset mine after regering and got rid of the pinging I was experiencing at very low revs when loading it up the my 4.0L

For the record - as someone is bound to ask...
  1. Disconnect the POSITIVE battery Terminal and touch it to ground for 30 seconds to discharge the PCM capacitors, which maintain the Adaptive Memory.
  2. Reconnect the Battery Cable.
  3. Turn Ignition Switch to the “On” position but DO NOT start the engine.
  4. Turn Headlight On.
  5. Turn Headlights Off.
  6. Turn Ignition Key Off.
PCM is reset
LINK to quoted info​
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responding to old post- sorry. But doesn’t disconnecting only the positive pose a threat of shorting the system if your tool touches Somewhere else while attached ? I guess this requires focus and precision . As far as grounding the positive cable with the negative still attached , is that safe to do too? Or did you remove the negative before all of this?
 
ndaddy said:
responding to old post- sorry. But doesn’t disconnecting only the positive pose a threat of shorting the system if your tool touches Somewhere else while attached ? I guess this requires focus and precision . As far as grounding the positive cable with the negative still attached , is that safe to do too? Or did you remove the negative before all of this?
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yes, don't let your wrench touch the battery terminal and any other metal nearby at the same time.
 
freedom_in_4low said:
yes, don't let your wrench touch the battery terminal and any other metal nearby at the same time.
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makes sense, thanks. and then once the red is disconnected is the cable still "hot"? how is one to ground it if cant touch other metal?

i guess part two is "reconnecting" the red cable- isnt that typically done before the negative is connected (which remains connected in this case? what dangerous / cautions here?
 
Once you disconnect a single cable from the battery, either positive or negative, the battery is isolated from the Jeep. It makes no difference which one you disconnect as far as disconnecting power. If you disconnect the positive terminal and then allow a wrench to touch the positive battery terminal and ANY ground it will short the battery. If you disconnect the negative terminal and then touch the negative battery terminal to any ground you will simply reconnect the battery. Obviously disconnecting the negative terminal is much safer although not many people do that.
 
pagrey said:
Once you disconnect a single cable from the battery, either positive or negative, the battery is isolated from the Jeep. It makes no difference which one you disconnect as far as disconnecting power. If you disconnect the positive terminal and then allow a wrench to touch the positive battery terminal and ANY ground it will short the battery. If you disconnect the negative terminal and then touch the negative battery terminal to any ground you will simply reconnect the battery. Obviously disconnecting the negative terminal is much safer although not many people do that.
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so if negative was disconnected then positive, positive was grounded, reattached positive then negative, pressed break/flashed light etc would this still reset the PCM?
 
Just disconnecting the battery will work, if you want to touch the cables there's no issues with that either. You don't need to operate the brakes or lights. You aren't really resetting the pcm, you are just clearing the temporary or short term memory. All the long term values are stored in non volatile memory and wont be changed. It really serves almost no purpose at all but can be an easy way to reset trouble codes if you don't have a scanner. Pulling the cable wont cause the PCM to do any re-learn procedures or anything special really.
 
If you want to verify the PCM was reset just turn the ignition key to the on position. After something like 90 seconds the check engine light will flash indicating the ready monitors are not set (because you just cleared them).
 
WallyWest said:
If you have the time just disconnect positive cable, go to bed. Reconnect in the morning, done.
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Disconnecting the negative connector does the same thing but with less danger of welding the wrench to the tub with the positive post being less than an inch from the tub.
 
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There is absolutely ZERO benefit to "resetting" the PCM BESDIES trying to clear codes without a code reader. Touching the battery terminals together is not going to fix a problem you are having. Ever.
 
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Lou said:
There is absolutely ZERO benefit to "resetting" the PCM BESIDES trying to clear codes without a code reader. Touching the battery terminals together is not going to fix a problem you are having. Ever.
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True though it's always a good idea to reset the PCM before driving it after you've installed a new sensor like a TPS, CPS, O2 sensor, etc.
 
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Lou said:
There is absolutely ZERO benefit to "resetting" the PCM BESDIES trying to clear codes without a code reader. Touching the battery terminals together is not going to fix a problem you are having. Ever.
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I disagree based on the experience I described earlier in this thread. I cleared the codes several times before trying a reset.
 
RMETeeJay said:
I disagree based on the experience I described earlier in this thread. I cleared the codes several times before trying a reset.
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It's been my experience that a "hard" reset, by cutting power, causes the engine to run noticeably different for a bit. While clearing codes doesn't.

What I've heard is the computer uses historical data to create a basic profile for how the engine runs, and that's what it relies on when you first start the engine. But once it's up to operating temp it should be using the data it's reading from the sensors in real time to determine what it's doing. So in theory at least you don't need to reset anything, just drive it and a day or two at most after new sensors, or whatever, are installed it should be up to speed.

That's what I've heard anyway from people who do custom PCM tuning.
 
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RMETeeJay said:
I disagree based on the experience I described earlier in this thread. I cleared the codes several times before trying a reset.
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What did you use to clear the codes? Did it also reset all readiness monitors and reset the fuel trims?
 
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