Resetting PCM
#1
03-08-2003, 01:52 PM
Resetting PCM
Could someone please explain to me why they suggest turning on the headlights after disconnecting the Negative battery terminal when resetting the PCM. IMHO it does absolutely nothing. Except help in passing the time away waiting for a minute to pass. Once the ground is removed every thing dies. The headlight circuit wires do not connect anywhere to the PCM. Curious
Regards
Jean Marc Chartier
Regards
Jean Marc Chartier
#2
03-09-2003, 06:25 PM
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Basically it is to insure all DC power is gone. Even when you disconnect the battery neg. cable there can be some residule DC power in the system.
I do kind of agree with you and don't think there is enough to cause any static discharge when removing the superchip.
The concern is you do NOT want any type of static electrical discharge when removing the chip or touching anything inside the computer (PCM).
To do this you should always be touching a metal part (Casing) of the computer this will insure YOU don't discharge any static to the chip or computer, by touching the metal case you are grounding yourself and thus preventing an static electrical discharge.
It does not take much, and usally will never notice any discharge, to make the chip, and or any componets on the computer worthless. That could prove to be a very expensive discharge.
For what it's worth, even though I agree with you about the headlights it is cheap insurance. All that is really needed is like 30 seconds if that, by that time all DC juice will be drained.
Hope that helps...
I do kind of agree with you and don't think there is enough to cause any static discharge when removing the superchip.
The concern is you do NOT want any type of static electrical discharge when removing the chip or touching anything inside the computer (PCM).
To do this you should always be touching a metal part (Casing) of the computer this will insure YOU don't discharge any static to the chip or computer, by touching the metal case you are grounding yourself and thus preventing an static electrical discharge.
It does not take much, and usally will never notice any discharge, to make the chip, and or any componets on the computer worthless. That could prove to be a very expensive discharge.
For what it's worth, even though I agree with you about the headlights it is cheap insurance. All that is really needed is like 30 seconds if that, by that time all DC juice will be drained.
Hope that helps...
#3
03-09-2003, 07:22 PM
01,
Please explain what you mean by residual DC power. A I have been taught; when a circuit is opened current flow stops. The only thing that can store current is a capacitor or a battery. The only way they can discharge is to close their circuit. When you disconnect the battery you have opened the circuit. Turning on the head light switch is not going to discharge anything. The circuit is open at the battery. You are just increasing the length of an open circuit. When you fail to ground yourself properly and spark the PCM that is not caused by not waiting long enough or by failing to “turn on the head light switch”. It is caused by the build up of voltage between your body and the part you touch.
JMC
Please explain what you mean by residual DC power. A I have been taught; when a circuit is opened current flow stops. The only thing that can store current is a capacitor or a battery. The only way they can discharge is to close their circuit. When you disconnect the battery you have opened the circuit. Turning on the head light switch is not going to discharge anything. The circuit is open at the battery. You are just increasing the length of an open circuit. When you fail to ground yourself properly and spark the PCM that is not caused by not waiting long enough or by failing to “turn on the head light switch”. It is caused by the build up of voltage between your body and the part you touch.
JMC
#4
03-09-2003, 08:14 PM
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Logically speaking in a simple circuit when the circuit is open (disconnecting the battery) current flow ceases. So you would be correct. However most circuits are not simple circuits. An easy example would be a big DC power supply. Take a variable DC power supply that is capable of putting out 15 amps at 170VDC. This DC supply would be powered by a wall outlet of 115VAC.
In order to have the ability of a variable supply and clean DC current the supply would have transformers and capacitors (filter capacitors etc) inside the circuit. They would store energy for a short time until discharged. This would be easy to witness because if you left something connected to the DC supply and then just shut the power off you would not see the voltage meter return from say 100VDC to 0VDC, it would take a little time, perhaps 10 seconds or so. If you had a DC light connected to the circuit you would notice it does not simple go from bright to no light like a standard 115VAC light bulb does. It would be something like a diode, and what you would see is it would be bright and once you turned the power off it would slowly dim until no further light. That is basically the same principle with the headlights draining any remaining power from the system.
In a simple circuit when you turn the power off you would see the needle drop to 0VDC immediately rather then a slow gradual movement.
Your statement:
“When you fail to ground yourself properly and spark the PCM that is not caused by not waiting long enough or by failing to “turn on the head light switch”. It is caused by the build up of voltage between your body and the part you touch.”
You are correct. I did not explain that as I should have. There is two possible problems, one if there is some residual DC power in the circuit and if you do not remove the chip properly you could produce a spark very little, most likely, unseen spark. An example of a much higher potential would be if you removed the hot side of the battery and touched part of the metal frame. The chances of that happen are remotely unlikely, but it is always a possibility and that is why they recommend turning the headlights on to insure “all” DC power is drained from the circuit.
The second and much more common problem is as you mentioned. If you do not discharge the static electricity from your own body by touching the metal frame of the computer you can possible damage the chip and/or computer due to static electrical discharge. It is also necessary to continue to touch the metal frame while removing the chip until it is completely removed. Just because you discharge yourself does not mean you will not create and store static electricity within seconds after initial discharge.
This is why in factories working with any type of integrated circuits (chips) people have to always wear a grounding strap to prevent against electrical static discharge (ESD) into a chip or circuit board they may be working with. It takes very, very little static electricity to completely render an integrated circuit or chip useless. It is very important to handle any chip which is an integrated circuit with care. So back to the headlights, it is nothing more then a safety measure.
EDIT:
The other important thing to remember is to never touch the metal pins on the chip, even when it is not installed. You can damage a chip just by touching the metal pins on the chip if not properly grounded.
In order to have the ability of a variable supply and clean DC current the supply would have transformers and capacitors (filter capacitors etc) inside the circuit. They would store energy for a short time until discharged. This would be easy to witness because if you left something connected to the DC supply and then just shut the power off you would not see the voltage meter return from say 100VDC to 0VDC, it would take a little time, perhaps 10 seconds or so. If you had a DC light connected to the circuit you would notice it does not simple go from bright to no light like a standard 115VAC light bulb does. It would be something like a diode, and what you would see is it would be bright and once you turned the power off it would slowly dim until no further light. That is basically the same principle with the headlights draining any remaining power from the system.
In a simple circuit when you turn the power off you would see the needle drop to 0VDC immediately rather then a slow gradual movement.
Your statement:
“When you fail to ground yourself properly and spark the PCM that is not caused by not waiting long enough or by failing to “turn on the head light switch”. It is caused by the build up of voltage between your body and the part you touch.”
You are correct. I did not explain that as I should have. There is two possible problems, one if there is some residual DC power in the circuit and if you do not remove the chip properly you could produce a spark very little, most likely, unseen spark. An example of a much higher potential would be if you removed the hot side of the battery and touched part of the metal frame. The chances of that happen are remotely unlikely, but it is always a possibility and that is why they recommend turning the headlights on to insure “all” DC power is drained from the circuit.
The second and much more common problem is as you mentioned. If you do not discharge the static electricity from your own body by touching the metal frame of the computer you can possible damage the chip and/or computer due to static electrical discharge. It is also necessary to continue to touch the metal frame while removing the chip until it is completely removed. Just because you discharge yourself does not mean you will not create and store static electricity within seconds after initial discharge.
This is why in factories working with any type of integrated circuits (chips) people have to always wear a grounding strap to prevent against electrical static discharge (ESD) into a chip or circuit board they may be working with. It takes very, very little static electricity to completely render an integrated circuit or chip useless. It is very important to handle any chip which is an integrated circuit with care. So back to the headlights, it is nothing more then a safety measure.
EDIT:
The other important thing to remember is to never touch the metal pins on the chip, even when it is not installed. You can damage a chip just by touching the metal pins on the chip if not properly grounded.
Last edited by 01 XLT Sport; 03-09-2003 at 08:23 PM.
#5
03-09-2003, 09:00 PM
A light bulb emits light from the heat created by current going through a fillament. As soon as you open the circuit it starts to cool. It will still emit heat and light till it cools enough to stop emitting light. The head light circuit is one of the most basic circuits around. All the circuits in the vehicle are DC except for the Alternator which used diods to creat DC current. The only other complicated circuits are the coils which are not energized when the vehicle is off.
JMC
JMC
#6
03-09-2003, 09:26 PM
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Originally posted by JMC
A light bulb emits light from the heat created by current going through a fillament. As soon as you open the circuit it starts to cool. It will still emit heat and light till it cools enough to stop emitting light. The head light circuit is one of the most basic circuits around. All the circuits in the vehicle are DC except for the Alternator which used diods to creat DC current. The only other complicated circuits are the coils which are not energized when the vehicle is off.
JMC
A light bulb emits light from the heat created by current going through a fillament. As soon as you open the circuit it starts to cool. It will still emit heat and light till it cools enough to stop emitting light. The head light circuit is one of the most basic circuits around. All the circuits in the vehicle are DC except for the Alternator which used diods to creat DC current. The only other complicated circuits are the coils which are not energized when the vehicle is off.
JMC
Yes a household light bulb has light due to current running across the filament inside the bulb. This action of current running through the filament creates a byproduct which is heat. However a diode does not have a filament and is completely dependant upon a DC current being conducted between the anode and cathode to create light. Diodes create very, very little heat and thus this is why they can last for many years.
If you take my example of a diode connected to a DC supply and leaving it connected when turning off the DC supply it will slowly dim until there is no visible light. That would be due to the residual DC current still in the system. If you just disconnect the diode from the circuit it will go from bright to no light instantly because there is no DC current being conducted through the anode and cathode.
Yes the lighting system on a vehicle is a simple circuit. The coils do retain some, a small amount of power in them for a short amount of time, less then seconds and they are discharged. I honestly could not tell you how much residual DC current is left in the system and for how long with our trucks. It wouldn’t be long. The battery does power the computer until disconnected. I can not tell you how long it takes for the computer to discharge its residual DC current after the battery is disconnected. I would say it would most like be a matter of seconds until all residual DC current is discharged. That is the reason some people recommend turning the lights on it will accelerate the time it takes to discharge any residual DC current in the system.
The important thing to remember is with any DC circuit there will be some residual DC current left in the system even after being disconnected from its power supply. How long is hard to determine. As far as our trucks it would be very little time until completely discharged, but not as soon as the battery is disconnected.
#7
03-10-2003, 08:53 AM
I did not use the heat analogy for the diode. A led does not use heat to creat light. An alternator uses a diod as a gate. It is not a LED but a simple diode. My point is that by the time an individual goes around from the battery to he head light switch the simple circuit is dead. As soon as you open the battery circuit by removing the negative terminal the circuit dies. If I understand what you are typing, you are telling me that by closing one switch on a circuit that has had its power source disconnected you are draining residual power from that circuit? How? Please do not get me wrong. I am ignorant and I want to learn.
JMC
JMC
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#8
03-10-2003, 10:35 AM
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Originally posted by JMC
I did not use the heat analogy for the diode. A led does not use heat to creat light. An alternator uses a diod as a gate. It is not a LED but a simple diode. My point is that by the time an individual goes around from the battery to he head light switch the simple circuit is dead. As soon as you open the battery circuit by removing the negative terminal the circuit dies. If I understand what you are typing, you are telling me that by closing one switch on a circuit that has had its power source disconnected you are draining residual power from that circuit? How? Please do not get me wrong. I am ignorant and I want to learn.
JMC
I did not use the heat analogy for the diode. A led does not use heat to creat light. An alternator uses a diod as a gate. It is not a LED but a simple diode. My point is that by the time an individual goes around from the battery to he head light switch the simple circuit is dead. As soon as you open the battery circuit by removing the negative terminal the circuit dies. If I understand what you are typing, you are telling me that by closing one switch on a circuit that has had its power source disconnected you are draining residual power from that circuit? How? Please do not get me wrong. I am ignorant and I want to learn.
JMC
First, you are far from being ignorant. In my opinion you do seem to understand the circuit quite well. The residual DC current is a hard concept for a lot of people to understand. Mainly because most circuit we see in our homes act just as you say “turn the power off and there is no current in the system.”
I knew what you were talking about with the heat and light, same as diodes in the alternator. I was using a “LED” as an example to try and explain how in some DC circuits when you disconnect power there is some residual DC current left in the system that drains off, or discharges. This does not take much time at all and usually in milliseconds. The point I was trying to make with the “LED” is when you have more then a simple circuit of which our trucks and most electrical devices have more then a simple circuit you will have some, little as it may be, but some residual DC current left in the system that just does not go away as soon as power is shut off or disconnected.
You know I have not tried this on my truck and I may tonight. Maybe you might want to. At night with your truck like in your driveway turn your headlights on, then off and see if they act like your house lights. In other words they go from being bright to instantly being dark, no dimming effect. If they do in fact dim as they shut down this may help you to understand what I am saying about the “LED” and gradual dimming until off (when still connected to a DC circuit). When I say dim, I don’t mean they will take like 5 seconds to dim to complete darkness, most like less then a second, but it would be noticeable.
I do agree with you about having to turn the headlights on. By the time you disconnect the battery then take the panel off to get to the computer, and then take the cover off the lights will not really do anything for you since there would have been plenty of time for any residual DC current to drain, discharge off.
I use to design automated test equipment, including the circuit boards, and develop the software to control it. The reason I am aware of the residual DC current in a system once power has been disconnected is one of the systems I developed would do a DC Hipot test on the motor windings prior to the actual motor test.
The DC Hipot would apply 500VDC to the motor windings. If I did not short the motor windings to ground prior to testing it could and sometimes would destroy circuit boards due to the residual current left in the windings. The other thing that would happen is if someone only did the 500VDC Hipot and then picked up the motor before it was discharged would get a static shock. Nothing that would medically hurt them, but quite the shock. That would be the same thing that could happen if right after you shut the motor off in your truck and you were able to touch an exposed part of the coil windings in the coil you would get a nice shock from it. It would not stay in the coil long, but it would be there for a measurable time after you turned power off to the engine.
#9
03-10-2003, 11:47 AM
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#10
03-10-2003, 01:24 PM
Norm,
I disagree with that. The headlight circuit is no where near the PCM. It runs battery to switch to relay and back to battery. Disconnect the battery, the circuit is allready open when the light switch is off, and you accomplish nothing by closing the headlight switch. A capacitor is a storage device. It will discharge if its circuit is closed. When power to the PCM is cut all circuits are opened. The capicator can not discharge.
Iit is the spark that is created by your body touching the pcm that will destroy the PCM citcuits.
01,
I understand what you are saying. I realize how a LED works. Photons are released when the electrons fill the voids caused by the doping. So if I understand it right the electrons do not stop releasing photons immediatly after the circuit is open. Do they have momentum to keep them moving? Or is it just the realignment of electrons happening?
JMC
I disagree with that. The headlight circuit is no where near the PCM. It runs battery to switch to relay and back to battery. Disconnect the battery, the circuit is allready open when the light switch is off, and you accomplish nothing by closing the headlight switch. A capacitor is a storage device. It will discharge if its circuit is closed. When power to the PCM is cut all circuits are opened. The capicator can not discharge.
Iit is the spark that is created by your body touching the pcm that will destroy the PCM citcuits.
01,
I understand what you are saying. I realize how a LED works. Photons are released when the electrons fill the voids caused by the doping. So if I understand it right the electrons do not stop releasing photons immediatly after the circuit is open. Do they have momentum to keep them moving? Or is it just the realignment of electrons happening?
JMC
#11
03-10-2003, 05:48 PM
Former Sponsor
Hi JMC,
We've had this specific discussion before....................
What actually has power & when varies across all the model years in the F-150 (& other vehicles too. There are differences in some of the harness routings, etc., less than half of them are documented anywhere in our experience. We run into all kinds of funny things in these OBD-II F-150 vehicles in everything from installing kill switches (which are required anytime you relocate a battery or at certain speeds and in certain classes at the drag strip, etc.) to line-locks, to you name it.
As you & I have discussed in the past, the preferable way to accomplish clearing the PCM in *any and all* computer-controlled vehicles, and what we actually do here at Performance, is to disconnect the battery and then cycle the ignition to the "On" position so that the PCM is in the loop so to speak, regardless of any differences in wiring harness, assembly line, make, model, etc., & there is a large immediate demand for power across much of the system. The PCM is effectively drained of residual current in *all* vehicles using this method. Then we turn the ignition back off & reconnect the battery. Pretty simple.
You can drain residual current in 30-60 seconds like this, but we still say to leave it like that for a few minutes "just because."
We've had this specific discussion before....................
What actually has power & when varies across all the model years in the F-150 (& other vehicles too. There are differences in some of the harness routings, etc., less than half of them are documented anywhere in our experience. We run into all kinds of funny things in these OBD-II F-150 vehicles in everything from installing kill switches (which are required anytime you relocate a battery or at certain speeds and in certain classes at the drag strip, etc.) to line-locks, to you name it.
As you & I have discussed in the past, the preferable way to accomplish clearing the PCM in *any and all* computer-controlled vehicles, and what we actually do here at Performance, is to disconnect the battery and then cycle the ignition to the "On" position so that the PCM is in the loop so to speak, regardless of any differences in wiring harness, assembly line, make, model, etc., & there is a large immediate demand for power across much of the system. The PCM is effectively drained of residual current in *all* vehicles using this method. Then we turn the ignition back off & reconnect the battery. Pretty simple.
You can drain residual current in 30-60 seconds like this, but we still say to leave it like that for a few minutes "just because."
#12
03-11-2003, 03:06 PM
Mike,
Yea I know, but I was in one of those moods.
If you are going to turn on the lights you might as well dance around the truck and chant; "drain, you residual current devel!" 
for all the good it does.
I also offer voodo chants to keep the tires from going flat.
Besides I am still waiting for 01 to get back to me on the photons. I want to know why the LED still glows.
JMC
Yea I know, but I was in one of those moods.
If you are going to turn on the lights you might as well dance around the truck and chant; "drain, you residual current devel!" for all the good it does.I also offer voodo chants to keep the tires from going flat.
Besides I am still waiting for 01 to get back to me on the photons. I want to know why the LED still glows.
JMC
#13
03-11-2003, 03:24 PM
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Originally posted by JMC
Norm,
I disagree with that. The headlight circuit is no where near the PCM. It runs battery to switch to relay and back to battery. Disconnect the battery, the circuit is allready open when the light switch is off, and you accomplish nothing by closing the headlight switch. A capacitor is a storage device. It will discharge if its circuit is closed. When power to the PCM is cut all circuits are opened. The capicator can not discharge.
Iit is the spark that is created by your body touching the pcm that will destroy the PCM citcuits.
JMC
Norm,
I disagree with that. The headlight circuit is no where near the PCM. It runs battery to switch to relay and back to battery. Disconnect the battery, the circuit is allready open when the light switch is off, and you accomplish nothing by closing the headlight switch. A capacitor is a storage device. It will discharge if its circuit is closed. When power to the PCM is cut all circuits are opened. The capicator can not discharge.
Iit is the spark that is created by your body touching the pcm that will destroy the PCM citcuits.
JMC
#14
03-11-2003, 04:59 PM
Norm,
When you disconnect the battery you have opened all the circuits. Presumably you have turned off the engine so any residual Current left in the coils and the Alternator is gone. Now the head light circuit is open now in two places, one at the negative post of the battery and one at the headlight switch. By turning on the switch all you have done is increase the length of wire from the switch to the positive pole of the battery. You still do not have a closed circuit.
My point is it is a waste of time to turn the headlights after the battery disconnect because it doesn’t do any thing.
Now a capacitor will not discharge unless its circuit is closed. If when you pull the negative terminal of the battery you close a capacitor circuit by means of a transistor or some sort of a relay it will discharge. By the time you walk around to the door, open it, reach in and pull the Chip the circuits are dead. If you have to remove the PCM it will take even more time because you have to undo the bolt holding the connector on the PCM.
If you create a spark by means of static electricity or such and blow a circuit in the PCM it is not caused by having failed to discharge any residual power. By the time you create the spark the PCM circuits are dead. It is because you sparked.
JMC
When you disconnect the battery you have opened all the circuits. Presumably you have turned off the engine so any residual Current left in the coils and the Alternator is gone. Now the head light circuit is open now in two places, one at the negative post of the battery and one at the headlight switch. By turning on the switch all you have done is increase the length of wire from the switch to the positive pole of the battery. You still do not have a closed circuit.
My point is it is a waste of time to turn the headlights after the battery disconnect because it doesn’t do any thing.
Now a capacitor will not discharge unless its circuit is closed. If when you pull the negative terminal of the battery you close a capacitor circuit by means of a transistor or some sort of a relay it will discharge. By the time you walk around to the door, open it, reach in and pull the Chip the circuits are dead. If you have to remove the PCM it will take even more time because you have to undo the bolt holding the connector on the PCM.
If you create a spark by means of static electricity or such and blow a circuit in the PCM it is not caused by having failed to discharge any residual power. By the time you create the spark the PCM circuits are dead. It is because you sparked.
JMC