resetting the PCM / ECU...?
- Thread starter Kevin D
- Start date
Viper Wizard
Enthusiast
You could buy a scan tool or unbolt the + terminal and ground it! 
Steve 00RT/10
Enthusiast
You could buy a scan tool or unbolt the + terminal and ground it!
Chuck's the man. What I've done in addition is to pull the 3 PCM plugs. Might not be necessary, but it completely isolates the PCM from any wiring. As Chuck indicates, use a drain wire from the positive post to a good ground to drain off any capicitance remaining. You can see it drain off with a digital voltmeter. if you don't drain it, it will take a little while to go brain dead.
Steve
Viper Wizard
Enthusiast
To do a field dump of memory, leave the PCM hooked up and disconnect the + terminal and then ground it for ten seconds.
Steve 00RT/10
Enthusiast
Chuck,
While we're on the brain resetting issue: I just went out and tried that with our car. After 10 seconds of drain, I still had about 15 mv in there. 45 seconds -- still at 5 mv. I then went and ran the car to see if my idle had reset it self to a new 'state.' It had not lost what ever bad things it somehow likes to do. How many mvs is considered brain dead?
I thought you once said that the only way to really clear the memory was to disconnect the battery at the back. I never did that, but found the above method (disconnect both front terminals, unplug the PCM, and then drain the capicitance off -- I can get it 1-2 mvs in about 30 seconds) to work for getting my idle completely normal for several start cycles.
The reason I'm kind of up on this is that I still have a pesky idle issue which nothing seems to solve....so I occassionally clear the brain and all is well for a few start cycles. Not a big deal. I just need to blip the throttle once coming to a stop from 40 MPH and up. Wants to idle down and sometimes (not all the time) die before coming back to normal. Ironically, pushing the clutch in at highway speeds does not initiate the almost die off syndrome. I've done all the suggested stuff: New battery, clean IAC, new IAC (from you), tube in the IAC hose, additional grounding -- TPS. This is the only little annoying thing the SC has brought. Strangely enough, our other SC car has idle hang -- just the opposite. Tried all of the above with it as well.
Bottom line is that just draining from the positive post w/o doing the other things listed above, does not reset my idle. I've also shown the TPS the new range. TPS idle voltage is normal on both cars. Kind of getting off track here, but still curious about the method to achieve a brain dead state.......or better yet.....a new idea to try to fix the idle issues.
Steve
While we're on the brain resetting issue: I just went out and tried that with our car. After 10 seconds of drain, I still had about 15 mv in there. 45 seconds -- still at 5 mv. I then went and ran the car to see if my idle had reset it self to a new 'state.' It had not lost what ever bad things it somehow likes to do. How many mvs is considered brain dead?
I thought you once said that the only way to really clear the memory was to disconnect the battery at the back. I never did that, but found the above method (disconnect both front terminals, unplug the PCM, and then drain the capicitance off -- I can get it 1-2 mvs in about 30 seconds) to work for getting my idle completely normal for several start cycles.
The reason I'm kind of up on this is that I still have a pesky idle issue which nothing seems to solve....so I occassionally clear the brain and all is well for a few start cycles. Not a big deal. I just need to blip the throttle once coming to a stop from 40 MPH and up. Wants to idle down and sometimes (not all the time) die before coming back to normal. Ironically, pushing the clutch in at highway speeds does not initiate the almost die off syndrome. I've done all the suggested stuff: New battery, clean IAC, new IAC (from you), tube in the IAC hose, additional grounding -- TPS. This is the only little annoying thing the SC has brought. Strangely enough, our other SC car has idle hang -- just the opposite. Tried all of the above with it as well.
Bottom line is that just draining from the positive post w/o doing the other things listed above, does not reset my idle. I've also shown the TPS the new range. TPS idle voltage is normal on both cars. Kind of getting off track here, but still curious about the method to achieve a brain dead state.......or better yet.....a new idea to try to fix the idle issues.
Steve
Viper Wizard
Enthusiast
YOU need to disconnect the + terminal AT THE battery and GROUND it! NOT at the + jump point! If you don't disconnect at the battery, YOU WILL NOT clear the PCM!
YOU WANT TO BE REAL CAREFUL DISCONECTING THAT WIRER AT THE JUMP POINT BECAUSE IF THAT STUD TURNS IN THE PDC, YOU WILL TAKE OUT YOUR ENGINE HARNESS!!!! A new harness is $2200.00!!
I typed this in CAPS because I have seen people do this!
YOU WANT TO BE REAL CAREFUL DISCONECTING THAT WIRER AT THE JUMP POINT BECAUSE IF THAT STUD TURNS IN THE PDC, YOU WILL TAKE OUT YOUR ENGINE HARNESS!!!! A new harness is $2200.00!!
I typed this in CAPS because I have seen people do this!
Steve 00RT/10
Enthusiast
YOU need to disconnect the + terminal AT THE battery and GROUND it! NOT at the + jump point! If you don't disconnect at the battery, YOU WILL NOT clear the PCM!
YOU WANT TO BE REAL CAREFUL DISCONECTING THAT WIRER AT THE JUMP POINT BECAUSE IF THAT STUD TURNS IN THE PDC, YOU WILL TAKE OUT YOUR ENGINE HARNESS!!!! A new harness is $2200.00!!
I typed this in CAPS because I have seen people do this!
OK...so you did mean from the back. Not to worry -- I have a battery shut off switch mounted in the front. I can clear the brain for my purposes by doing the above I listed. If the computer is isolated completely from the back end......and the stud drained down......what further impact on PCM memory comes from the back?
Good to know about the stud twisting. If that's the case, it seems sheer idiocy that a factory installed jam nut was not put below the terminal, with instructions to grab it before removing the top nut. How would anyone know this unless there were instructions and a warning in big bold type???
Steve
Wow, I didn't know this could happen. I've disconnected that postive cable a few times to clear the PCM but the stud had never budged. I think I'll follow Steve's lead and install that battery shut off switch.
Viper Wizard
Enthusiast
Shut off switch WILL NOT do it! It will not isolate the electrical system! I think a shut off switch is a waste of money! A battery tender is better!
Again, to clear/reset a PCM you need to get to the end of the electrical loop of the Viper AND that is at the positive terminal on the BATTERY AND then you ground it!
Come on guys, read what I write! I didn't start yesterday!!
Again, to clear/reset a PCM you need to get to the end of the electrical loop of the Viper AND that is at the positive terminal on the BATTERY AND then you ground it!
Come on guys, read what I write! I didn't start yesterday!!
VIPER BAZ UK
Enthusiast
Chuck is the mercanic LOL....................
Get that rear wheel off!!!!!!!!!!!!! Is it left or right side LOL!!!!!!!
Get that rear wheel off!!!!!!!!!!!!! Is it left or right side LOL!!!!!!!
Shut off switch WILL NOT do it! It will not isolate the electrical system! I think a shut off switch is a waste of money! A battery tender is better!
Again, to clear/reset a PCM you need to get to the end of the electrical loop of the Viper AND that is at the positive terminal on the BATTERY AND then you ground it!
Come on guys, read what I write! I didn't start yesterday!!
Since you're new here
I thought I'd ask this one: What is I disconnect the 3 connections on the PCM only? I assume that will reset it after a certain period of time but are they any ill effects?Steve 00RT/10
Enthusiast
Shut off switch WILL NOT do it! It will not isolate the electrical system! I think a shut off switch is a waste of money! A battery tender is better!
Again, to clear/reset a PCM you need to get to the end of the electrical loop of the Viper AND that is at the positive terminal on the BATTERY AND then you ground it!
Come on guys, read what I write! I didn't start yesterday!!
Just to be clear then -- I could disconnect the 3 PCM plugs and put the PCM on the shelf in my basement for a while -- reinstall it --- and it would still not be cleared of memory? I'm not getting something here.
I'll have to see a schematic to understand I guess. I think the radio may be tapped off along the line,but that's immaterial.Steve
Viper Wizard
Enthusiast
Sometimes it will clear BUT NOT all the time!
I feel like I am
! If you want to be sure your PCM to clear/reset, DISCONNECT the + terminal AT the battery and then ground it!
This is my last post on this thread!
I feel like I am
! If you want to be sure your PCM to clear/reset, DISCONNECT the + terminal AT the battery and then ground it!This is my last post on this thread!
Just to be clear then -- I could disconnect the 3 PCM plugs and put the PCM on the shelf in my basement for a while -- reinstall it --- and it would still not be cleared of memory? I'm not getting something here.
Steve
dave6666
Enthusiast
I think in the future when I reset the PCM that I'll do it from the positive battery cable in the wheel well.
Discuss?
Discuss?
Steve 00RT/10
Enthusiast
It doesn't make sense to me electrically. I'll continue to do as I have. It's always worked and is much easier. Even after quickly going through the wiring diagram in the manual....it still looks like you should be able to drain the PCM from the front. An actual schematic of the PCM system would be easier to see something else.
Steve
Steve
littlecaars
VCA Venom Member
Holy moly Chuck, that would be a mistake that one would never ever forget!
