BMW i8 will NOT charge, start or drive.

Harold M · 2024-12-14T08:34:24-0600

Take care. when removing or changing the heavy i8 12 volt battery.
There is a scrappy wiring loom that hangs down around the 12 volt. area. It looks like a leftover unimportant SENSOR near to the RED terminal cover
It's so easy to catch it when struggling to lift 12v in or out and detach it.
I DID BY ACCIDENT

CAR WAS SCRAP for a month whilst I searched the world for info.

Nowhere was it mentioned. People said I need new 12v, need new HV, need new on board charger.... thousands of dollars..... I needed NOTHING

Just sharp eyes from a DIY neighbor who spotted a tiny black wire terminal innocently hanging loose

We took off the RED terminal block, looked closely and saw this tiny plug could fit into a hole in the underside of this terminal.

Put it back together in minutes and VOILA

CAR BACK TO NORMAL FUNCTION

USD50k saved.

Good luck guys.

EvanstonI3 · 2024-12-14T09:07:31-0600

This is an i3 forum, not i8.

Gonville · 2024-12-14T09:30:34-0600

EvanstonI3 said:
This is an i3 forum, not i8.

Wonder if our is the same in that area?

mojo · 2024-12-14T11:55:24-0600

Gonville said:
Wonder if our is the same in that area?

I've no direct knowledge of the i8 (sadly) but I suspect not. The OP describes the i8's 12V battery as "heavy" so it seems likely that the design is very different. As you know, on the i3 REX there is no starter motor, but that can't be true of the i8, where the engine drives the wheels rather than an electrical generator (which serves as the starter as well on an i3). So I would expect the 12V side of the i8 to be more heavily based on an ICE type of wiring assembly.

alohart · 2024-12-14T14:29:45-0600

EvanstonI3 said:
This is an i3 forum, not i8.

@Harold M did post in the "Non BMW i3 Discussions > Off Topic" section, so his post about an i3's close relative is OK by me.

alohart · 2024-12-14T14:58:29-0600

mojo said:
The OP describes the i8's 12V battery as "heavy" so it seems likely that the design is very different.

i3's have a similar 12V battery positive terminal clamp used on other BMW's. They all contain an explosive charge to disconnect the 12V system during a significant accident. There are several small wires that connect to this terminal clamp on an i3. This area wasn't designed very well with wires not routed and enclosed as well as they could have been. When replacing the 12V battery on an i3, care needs to be taken not to damage these small wires, so it sounds similar other than the large, heavy battery.

mojo said:
As you know, on the i3 REX there is no starter motor, but that can't be true of the i8, where the engine drives the wheels rather than an electrical generator (which serves as the starter as well on an i3).

Our Honda Insight gasoline-electric hybrid was like the REx design in that it did not have the usual 12V starter motor even though the Insight engine directly drove the front wheels. Its 144V electric motor-generator was installed between the engine and the transmission. It started the engine as well as generated power to aid in vehicle propulsion and to charge its small battery pack. It was such an obvious solution that eliminated a conventional alternator and starter motor, yet I'm not aware of another HEV or PHEV that does something similar except Toyota's Hybrid Synergy System. Being mounted directly on the crankshaft and thus not requiring a solenoid to move a starter motor gear to mesh with teeth on the flywheel before the starter motor could spin the engine, it was silent unlike a conventional 12V starter motor and spun up the engine so fast that it started instantly. A negative to this design is that the electric motor could not propel an Insight on its own because the engine would be spinning creating significant drag. A decoupler between the engine and electric motor would have solved this deficiency.