[benim10]

Hello, my F11 started having crank issues out of nowhere. From firing up strong 20 minutes earlier, it barely cranked while starting. Connected jump wires which didn't make a difference until it started with no issues at all after a couple of minutes. Drove home with dropping voltage, dropped from 12v to 11.1v during the 10km drive home.

Popped in a new fully charged AGM battery today and reset codes in ISTA to no avail. I hear a solenoid when pressing the starter but the engine doesn't turn at all. Only real fault code i get is 243A00 - Preheating control unit Term 30 no voltage. Started checking voltage and ground under the hood aswell as on the battery. Battery at a steady 12.2 while i only get 2.6v under the hood. Doesn't change what ground spots i use, or if i check on positive jump point vs alternator positive point.

My theory is a jagged positive lead somewhere. Is there a way I can dive deeper in ISTA without pulling halv my interior out? Car is stuck in a tight parking space right now. Any ideas?

Best regards

[benim10]

When disconnecting the positive lead of the generator, the supply voltage under the hood goes back up. Makes no difference when trying to crank though. When ignition is off, i have a 5A draw each from no 3 and 6 on the diagram. Any help on how to carry on this diagnosis?

[benim10]

I connected a parallel plus cable from positive battery terminal to positive jump point and it fired right up. What is the most probable cause for voltage drop & amperage draw between the two terminals?

[Surly73]

Originally Posted by benim10

I connected a parallel plus cable from positive battery terminal to positive jump point and it fired right up. What is the most probable cause for voltage drop & amperage draw between the two terminals?

So I know I'm going to sound like a jerk, but obviously it will be the positive cable path from battery to under hood.

I am pretty sure there was a TSB / recall out for a number of earlier F10s for issues with the positive run from back to front which could cause melting and fire - you might want to see if there are any open recalls for your VIN. I believe it affected mine, I'll see if I can dig up any details.

I have also read about a number of problems with the power distribution box (I think it's called "Integrated Supply Module" under the hood near the blower motor. It has a number of large fuses sealed inside and is "not repairable", but actually is repairable if you're handy. Shop procedure is replace the $xxx box. This thread has some stuff in it that may give you some ideas.

I assume you've already cleared all the stuff on the positive terminal itself - there are fuses and pyro charges in that area.

Because you have massive voltage drop from back to front, as long as you have some kind of load (like ignition on) you can use a voltmeter along the path until you find a reading between two points to narrow it down. You need current draw along the path to trigger the drop from a dodgy connection though.

[boblefisk]

You should check the "under floor battery plug" where the positive terminal go through the chassies.
ive seen others with same problem, and it was bad corrosion on the cable underneath.
worth checkin out.
the corrosion is on the cable that is on the underside of the trunk.