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Mystery power disconnecting

4893 Views 13 Replies 5 Participants Last post by  d0ugmac1
It sits in snow after a couple of weeks and can be started no problem today. But running 10miles and after parked it 5min, it wont start. Actually it totally disconnected (won't response for door remote control, even the security light won't on while the door opens).

It can come back working if we leave it a while..

I thought the battery connect, but anything else can explain the mystery better?

Thanks a lot for your inputs!
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Bad ground strap(s)? Try using black jumper cable to connect battery terminal directly to engine or transmission bolt/bracket and retry. Very common for the transmission to body strap to fail.

What you are describing seems to be a thermally related electrical problem. This can be cause by a failing ground which heats up with continued use, causing a high resistance connection. Can also be a thermal expansion issue with major lug connection or electrical junction...which may or may not have corrosion related effects.

Start with a temporary 'hack' to improve your grounds. If you can swing it, use the red jumper cable to again jump the battery NEGATIVE to the car chassis...this is a temporary fix for both major ground straps. If no improvement, then you need to examine the positive path (ie battery to IPDM etc.)

Let us know how things progress
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Thank you very much d0ugmac1! I think you are right: it's not the connectors to the battery ± poles(I've put the new connectors after read your post) but somewhere else. The car can be started as long as it's cooled. Otherwise it simply be is if no battery installed at all!

Could you please describe the temp 'hack' more? I don't know what is chassis... and don't understand clearly how to make the temp better grounding etc.

Really appreciate your advise.

Ok, so a little more detail. Idea is to improve the path that the current to start your car takes, so that means from the battery to the starter motor and back around to the battery. We'll just ignore the fact that current actually flows from negative to positive, electrons being negatively charged and all.

Looks a little like this, in ASCII art for those that remember such foolishness:

Power Path
+Battery --> Starter solenoid --> Starter motor --> engine metal --> body metal --> -Battery

Control Path

+Battery --> IPDM --> ignition switch --> starter relay --> starter solenoid --> engine metal --> body metal--> -Battery

In both cases you see the 'engine metal' play a part. As you may recall the engine (made of steel and aluminum, both conductive materials) is supported by rubber engine mounts, which are non-conductive. To provide a high power path for the return currents generated by the alternator or used by the starter motor, then engine has a conductive connection to the metal body of the car (chassis) which then has another conductive connection to the negative terminal of the battery. Either one of these can go bad.

The engine to body connection on Gen3's is part of the negative battery cable that extends between the metal body work and transmission housing (driverside), under the battery tray. Usually the connection between the engine and the battery goes bad due to corrosion/mechanical fatigue at the mid-crimp point (battery to chassis) or the end crimp (battery to engine) connections.

The body to battery connection is just the black cable you see attached to the -ve terminal of your batter which goes a short distance and terminates on a bolt into the body sheet meta and then on to the transmission housing. Often the problem here is corrosion between the terminal and the body metal, or corrosion within the wire jacket itself.

The hack is to replace both of these electrical connections using something 'handy', like jumper cables (which anyone with a car or battery over 4 years of age should have). In this case instead of connecting two batteries in parallel, we are creating a Y connection from the battery negative to both the engine/transmission block of metal AND the body. You are looking for a large bolt head, or thick metal bracket that obviously is securely fastened to the main bulk of the engine/tranny metal. For the body connection, the 3 nuts used to hold the strut into the tower make a good and convenient choice.

For safety reasons I would do this in this order:

1. black jumper1 connector to battery -ve
2. black jumper2 connector to engine/tranny
3. red jumper connector1 to black jumper1 connector attached to battery -ve
4. red jumper connector2 to strut nut.

Attempt start.

EDIT if you need more slack lead between the #2 terminals you can safely split the wires further than they came from the factory. I would do it while the plastic is warm AND pull wires towards and away from you with the join between instead of just pulling them left and right as there is less chance of the insulation being torn from the side of one of the wires. You get better shearing action on the thin bit of plastic by ripping 'through' it instead of 'across' it.
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If the above doesn't work, try again with different terminating points on the engine and body. If that still doesn't work, it could something in the control circuit:

-starter relay
-starter solenoid
-starter motor power connection (+ve from battery fusible links)
-fusible links
-ignition switch

But my money is on a bad ground.
Thank you a lot d0ugmac1! I got a new battery negative terminal -> auto body -> engine body connector, cleaned up the oxygen sensor connection and a wire connector (maybe goes to transmission). The mystery power disconnecting (with warmed car) seems gone.

I noticed the security light is off when the car is running and it's flashing when the engine is turned off. Is that normal? I remember it's on steadily while running a month ago....


Security light off while running is correct. Flashing I believe means the system is armed and is completely normal (unless it is a very rapid blinking) 1-2 secs/blink are fine.

Looks like you fixed more than just your warm starting problem :)
The problem is that none of my work shot the critical spot.... The disconnecting happens today, and come back without much engine temperature drop.

I think it might be the security circuit problem(misconduct): Since that's the only part can complete shut down the system without notiable physical/mechanical change....

Anyway to trouble shotting that?

It doesn't make sense for 'everything' to disconnect. What exact make/model/year do you have? I"m pretty sure the dome light runs direct from battery, via security, no IPDM, no relay. If that sucker doesn't come on, you either have

a) bad battery (internal crack in terminal or plate)
b) bad battery cable (negative you've fixed, maybe positive?)
c) cracked main power wire or terminal (at battery side, or fusepanel side)

We know the fuse is good, and the battery isn't shorting that's about it.

Inspect the main power wire and connections from the +ve terminal into the fuse panel. Look for hairline cracks in all rigid metal parts.

Borrow a battery to see if that makes a difference.

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Since your car seems to be "all or nothing", it sounds like it is either the negative/ground (which you said you replaced) or the very first part of the positive line before it splits into other fuses. Problems anywhere else would conceivably allow for some aspects of the vehicle to still function

As d0ugmac1 said, it has to either be that or the battery itself. I think the easiest way to rule out one of those is to swap the battery.

If this were an older car (I guess 1993-2001 might be old enough), I'd start the car by running a positive line straight from the battery to the starter. But I do not know what effect (if any) that would have on the computerized cars of today.

EDIT: when it's dead, have you tested with a multimeter to see if you have continuity at all grounds or what your voltage is at the terminals?
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Forgive my ignorance, but what exactly is "the big 3"?
Forgive my ignorance, but what exactly is "the big 3"?
Adding additional grounding cables from battery, I personally think it makes most sense to do battery->chassis, battery->engine, engine->chassis (so a triangle, and if any one connection fails, the other two will provide redundancy. As a network guy I think you'd like that ;)
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