James Bailey

Where do the "extra" small + wires on the battery terminal on the later cars end up going ??Fuse panel ? And do these power the starter solenoid ?? Early cars power flows battery,starter,jump post, then central fuse relay board.

Bill Ball

I noticed the voltage going high and fluctuating when driving the car to my place, but it started OK after that. Later it did not start and had almost no electrical power (only the clock worked) but had power and started a few minutes later. Then on the way home the voltage fluctuated high again but then stabilized perfectly for the last 20 minutes of the ride. I didn't have the radio on.

I will go over the positive cable and engine harness more thoroughly and look for bad spot.

Dean_Fuller

Early signs of Ignition switch going?

pcar928fan

I was thinking ignition switch too Dean... Whenever I hear of crazy electrical stuff (especially on the S4 cars) the first thing I look at is the age/miles on the car and then if above about 75k (or 200k+ in this case!) I think ignition switch... Damn things cause the craziest $hit to happen to these cars. Things that seem COMPLETELY unrelated in fact!

Bill Ball

Sean: It was replaced recently. Alan and others have noted that a faulty ignition switch can't kill ALL power as the positive cable does not route through it.

John Speake

At least one of them powers the fuel and igntion ECUs...

Bill Ball

According to the wiring diagrams one small wire goes to the LH relay and another to the EZK relay via U11 and U12 on the CE panel. There are 2 other small wires off the positive post that go to the cooling fan amplifier via the CE panel (S12 -> fuse 29 -> Q22 and S11 -> fuse 28 -> Q21). I suppose if those have power during one of the incidents, that further implicates the large positive cable.

Landseer

Bill, if other examinations don't yield the cause, it might be reasonable to pull panel and check back.

Alan

There is also the direct feed to the PSD (right there above) for cars so equipped and the direct feed to the ABS controller in cabin (if equipped), and as noted before the 2 ECU feeds and the feeders for L/R cooling fan final stages. Unfortunately all these are unfused at the source (stupid!) - some are unfused the whole way...

Alan

Bill Ball

Can't hurt, but I'm not sure how the CE panel could kill essentially all power including power at the jump post, which is fed directly from the battery (via the starter and engine harness).

Alan

There is no point - if the jump post doesn't have power there won't be any power to the CE panel - so that can't be the culprit.

Its important to understand the flow - it is as Jim noted (except the small direct feeders above) Battery -> Starter -> Jump Post -> CE Panel -> Dashboard.

There is some variation as to where the alternator connects in the flow (either to the jump post or to the starter).

So debug has to proceed logically & methodically (esp. in the case of an intermittent issue) by isolating the failure sequentially...

Bill is on the right track and closing in...

Alan

G8RB8

I think you're going to find a loose or corroded connection at the starter positive post.

Alan

Bill already said he'd cleaned up the main starter connections...

Could be the wiring there corroded inside the sheath there - but apparently not the terminal connection itself.

Alan

Charley B

Never trust a report of a jump not working. We've all experienced hooking up a jump and nothing happening for two or three tries and then all of a sudden it jumps to life. I've even seen one dummy without a flashlight trying to do a jump start without removing the little cap off the jump post. OK, that was me, but I'm going to think of a good excuse why that happened.

My point being, when it happens again, try a jump at the jump post in order to confirm or eliminate that info from your trouble shooting.

outbackgeorgia

Battery probably has an internal crack inside just under the positive post. Not as unusual as one might think. Bad news is that the battery may explode, as the crack may be above the liquid electrolyte. If below, no problem.
If you have not seen the results of a battery explosion, this is not the way to find out. WEAR EYE PROTECTION as a MINIMUM when troubleshooting this one!
Sulfuric acid is blown everywhere due to the hydrogen explosion.
I would replace the battery now. Cheap compared with the potential issues.
Dave