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snapped ground cables & resulting behavior

1798 Views 7 Replies 4 Participants Last post by  krobinso
Could someone tell me why there are two ground cables? They're called "Transmission Ground" and "Engine Ground" or "sub ground."

I encountered an odd problem last night. The initial symptoms were that the car stalled as I was going around a corner, then seemed to require more gas than it should have to travel on flat ground, and assist was even kicking in on flat ground. The sound of the engine turning over was muted each time I turned the car on, and it didn't like to idle. Eventually the SOC meter went to zero and the car absolutely wouldn't idle. In fact, there was this weird behavior where: I turn the key, the car idles for about 1.5 seconds. The car stalls. The car comes back (as from an auto-stop) and idles for 1.5 seconds. This repeated with no intervention from me, until I took the key out of the ignition.

Well, a look under the hood revealed that _both_ the grounding cables had snapped. I can only assume that one snapped a while ago and the other was compensating, until it, too, went. Can anyone guess what would happen if one or the other ground was not present?

I've read this thread:

http://www.insightcentral.net/forum/vie ... php?t=3196

and intend to get some paste intended for creating an electrical connection between dissimilar metals. But in the meantime, my car still does not go.

I reconnected the grounds: the engine ground / sub ground with a 6-awg wire I had & the original nuts, and the transmission ground with my jumper cables. With that done, I hear the starter motor engaging and the engine turns over, but doesn't fire. I suspect that the tranny ground connection I made with the jumper leads isn't that good, so went out to get more 6-awg wire and crimp ends. But I'm not convinced that that connection would keep the engine from firing.

I have the shop manual (which hasn't been much help to this problem), but I don't have the "Electrical Troubleshooting" manual.

I'm mighty confused at this point. I don't know that much about cars --- never owned one before this Insight. For all I know the problem could simply be that I flooded the engine, by giving it gas when it was running on assist-only (before I realized that the ground cables had snapped). But I'm an electrical engineer, so I'm going to clean the electrical leads and get out there with cable, crimpers, and a voltmeter/ohmmeter to see if I can fix the problem.

I suspect that the engine isn't firing because the computer thinks it shouldn't. I've seen this happen on an old volvo before. due to a bad electrical connection to that car's microprocessor.

Well, that's my story. My questions are:

Does anyone know why there are two ground cables, or what specifically the "transmission ground" is for?

Does anyone know enough about the computers' state machine to explain why the car would let itself run on assist only, or other consequences of running the car with no engine or transmission ground?

Thanks very much,

Karen
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krobinso said:
<snip>

Well, that's my story. My questions are:

Does anyone know why there are two ground cables, or what specifically the "transmission ground" is for?

Does anyone know enough about the computers' state machine to explain why the car would let itself run on assist only, or other consequences of running the car with no engine or transmission ground?

Thanks very much,

Karen
As an electrical engineer I hoped you'd have the answer. I don't think there's a valid design reason except for redundancy. And it appears it kept you going a few more miles :!: :)

Assist is _supposed_ to do just that (give assist) on acceleration. I don't think the system is "smart" enough to realize the ICE (Internal Combustion Engine) had "died".

Not sure of some of the other ground locations and the possible overload (Read, Smoke :!: ) from loosing the big'uns. Basically any of the smaller ground that attach to the engine could have been overloaded. G101 is the main ECM ground and is located on the engine block, under the "beauty" cover and just to the left (driver's side) of the oil filler cap. Severe overloading of these wire(s) can cause cross circuiting in the looms and damage to other components. ($$$) If the insulation is visibly "blistered" near the ground screw points then further inspection is highly advised before any more key on time :!: :!: :!:

HTH! :)

But I'd still recommend investing in an ETM (for the future) :)
 
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