No Crank issue
 

So I haven't driven the BMW in about two weeks. Usually I leave it on a small battery maintainer that I have, since I haven't been driving it very often. But the last time I drove it 2 weeks ago it started fine after sitting for a few weeks, so I didn't put it on this time.

Get in it to move it this time and put it in the garage. The last time I drove it, it started up just fine but after stopping and starting it again while hot (in a bank drive thru) it sounded like the starter solenoid was failing, and I was hearing the click with no start. Fortunately it started after four or five clicks, and later that day I had no issue starting it again cold. Anyways, was gonna put it in the garage and take the starter out yesterday, but it wouldn't start.

I get out the jumper cables and try to jump it -- but here's the tricky part. When I put the jumper cables on (seeing 14.5 volts at both the battery and the jump terminals under the hood) and I turn the key to start it, it just clicks and all the gauges on the dash start going down with every click.

I did some searching and it looks like this could possibly be the ignition switch causing a problem (perhaps causing my click/no start problem from a few weeks ago, though I recall that sounding different) but other than ordering one of those, what else could I be doing wrong?

Other observations: the cabin lights come on, the dash comes on, and the odo has not been reset as if I had disconnected the battery. I checked codes with my Foxwell NT510 and don't have the EWS/DME synchronization code, or any other codes that seem likely to cause the problem (just a couple for the secondary air system).

No Crank issue
 

If you can get to the starter apply +12 to the solenoid terminal to test if the starter turns also check the B+ terminal that it's tight (I recently disconnected mine to replace a starter).

You said the gauges are going down. Measure the B+ while attempting to crank. You might have a battery that's lost it's capacity and the current draw pulls the voltage down too far to crank. (similar symptom of open ground).

Thanks Andrew, is the B+ the one in the engine bay?



The gauges are going down and the engine doesn't turn over even when I am jumping it. I'm jumping it from my Prius with a brand new AGM battery in it, while the engine is running. It seems to me that battery voltage can't be the problem (I'm measuring 14.5 volts at the engine bay positive terminal before jumping). I didn't have a helper to watch the voltage while turning the key, but I'll see if I can get one later.

No Crank issue
 

Yup B+ should have a very large cable coming from trunk then at the jump point drop down to half size to go to starter and alternator.

You can measure voltage at the cig lighter

This is with the engine not running? 14.5v on a battery seems unlikely - you should see high 12s at best, unless there is a charger hooked up or the engine is running (same thing!). :confused:

That's when I have jumper cables hooked up to my X's battery and hooked up to my Prius's battery on the other end, while the Prius is running.

I get called on to help jump cars for folks a few times a year and I often see this when I arrive - they have a donor car running with jumpers hooked up but faulty car just clicks when start is attempted (and faulty car loses gauges, lights etc.).

In nearly every case it's been crappy jumper leads (not enough current capacity) or crappy jumper lead connections (one or more of the four required connections). The end result is the same - voltage looks good until you load the connections or leads with a few hundred amps of starter current, then the poor connections or cable cause a massive voltage drop (ohms law! V=IR) and the faulty car simply clicks.

Voltage doesn't start a car - current does. ;)

A REALLY screwed battery can also (in theory) cause this but that's less common.

I'll be darned, I think you were right wpoll -- I tried jumping it again (and found my alligator clamps for my DMM so I could watch the voltage while starting) and it started up this time. I made extra sure to get them as secure as possible -- it's really hard to get a good connection on the positive terminal on the battery! Anyways, thanks guys for your help, turns out it was a PEBKAC issue....again...

I'll be darned again, I let it idle for 10 minutes, drove it around for another 10 minutes, and when I parked it and turned the key all the lights went out -- battery is completely shot. Might explain why my trickle charger didn't work after almost 24 hours of charging, it might not have thought there was a battery on it at all.