Transmission Destroyed By Python 871xp

As I stated earlier, “I’m providing too much information to Circuit City which helps them prepare their defense.” So my participation in this part of the discussion is going to be very limited until after the trial. But . . . 

When is the last time you measured the impedance (not the resistance, the impedance) of the Python 871XP’s connections? You are making unwarranted assumptions about their circuit designs. We already know that some of their inputs sink enough current to power-up the module even with the ground disconnected. In my biomedical work this is a major design flaw; we often have to use optoisolators and other strategies for totally isolating inputs/outputs from each other and from the system’s main power supply. The fact that the alarm/remote-start module functioned quasi-normally indicates that some inputs can act as Vss with the system ground disconnected. This may not be a problem in most automotive applications, but when a marginal engineering practice coincides with an installation error, the result can be disastrous for the customer.

Thanks, Kar TuneMan, you’re dead on. I provided the information regarding the wiring error as a courtesy to help others avert a potential problem. I fully realize that I’m also providing an opportunity for some installers to start another round of, “gee, I don’t see how this could cause your problem.” I think most of the comments are prompted by a legitimate curiosity about the problem, but they will certainly be used by Circuit City to try to avoid accepting responsibility for this incident. Rest assured that I’m holding back a couple of aces that won’t be revealed until the end of game. And a few red herrings along the way should confuse the Circuit City people even more.

And now, time for a brief commercial message . . .

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How do you know their INPUTS sink current?  From what I remember it is actually the parking light output that sinks enough ground current to cause the alarm to do some funky stuff if a true ground isn't connected.

I'm not saying the inputs don't bleed current back to the system, but I wouldn't be confident that they did just because of what you saw (more testing needs to be done).

I would bet $10 (I know, big spender) that the tach wire is optoisolated.  I can't prove this at all, as I don't have a remote start unit laying around, but you have to remember that this is a mass produced electronic product by one of the biggest names in the business.  They may not optoisolate every input, but I am confident that they at least optoisolate their tach input.  As we all know, any noise on a tach wire can cause issues, this is enough of a reason to isolate it.  Also, keep in mind that they have been selling these things for years, and I have never (until you) heard of any issues caused by hooking up the tach wire.

Regardless of how/why it happened, I think you have an open and closed case.  They worked on your vehicle, your vehicle immediately broke, an independent shop found a problem, everything worked from then on.

Have you started filing the paperwork yet?  I am anxious to see how quickly CC pays up.

actually what mabuffalo says makes sense if you think about electronics in general and the given situation.  when the remote start engages, the unit "searches" for a tach signal from it's tach input, which causes that circuit path in the unit to close and allow current flow.  once or twice is enough to damage an electrical device as we all know.  electronics do funny things that we would never imagine when no properly used or installed.

also, even though you released this information, they have no way of using the info against you or in their defense.  the cut-and-dry fact is that the wrong connection was made, and that in turn caused the tranny to become damaged.  nothing omits the fact that the installer incorrectly installed the device and it subsequently damaged your vehicle.  their attorneys will see this and it will probably not make it all the way before a settlement is issued.  CC doesn't want it's name tarnished (ha, ha right?) by a lawsuit filed against them publically, so they will do what they can to avoid it.  as long as your not asking for a million dollars for "mental anguish" you should be fine.

It doesn't 'search' and it doesn't only do it when the vehicle is remote starter.

As I already said, I don't know exactly how the input works, but at a bare minimum it would be an input transistor.  Most likely it is an optoisolator, which is basically equivalent to an LED.  What happens if you ground out the base of an NPN transistor, or the + side of an LED?  Nothing.  What happens if you apply 14.4vdc to the base of a transistor or the + of an LED?  Assuming there is enough current availible (>0.002A) the transistor will go in to saturation and the LED would turn on.

The fact is, that you would have to have a very sensitive circuit to be damaged by either an LED or the base current of a transitor.  We are talking about a few milliamps here at most.

Now if they were somehow trying to energize a relay coil off the tach signal, I would have no problems agreeing that that could pose a problem, but I am very skeptical (not saying it couldn't) that this would damage a tranny. 

So, now, the big unknows are how much current can the tach wire pull and what is the function of the wire they tapped in to?  I used to have an old Viper 550ESP laying around but I got rid of it.  I might go ask for it back just to do some testing!!!

Start a new thread........

The lawsuit has been filed. I am going to refrain from further comments about the case until after it’s been decided, but I may reply to some general comments made earlier on this forum. If the thread remains “open,” I will post the outcome after the trial. Otherwise, you can check www.AddictionScience.net/CircuitCity.htm for the updates.

Meanwhile, do consider “buying them a cup of coffee.” The folks at www.the12volt.com provide a great service in hosting this forum and in their other work, and I can tell you from experience that even small, token contributions are sincerely appreciated by those of us who offer many of our services free of charge.