Problems with the cranking on my BMW F20 LCI

[coolguy]

Greetings everyone,

Just had trouble starting the car; I noticed it a few weeks ago, but being the slothful person that I am, I replaced the battery in the hopes it wasn't holding charge—a 200 pound error.


I believe I've isolated the problem to a power delivery issue after dragging myself out of bed one evening to conduct some diagnostics.

This is a list of all the symptoms I'm experiencing.

The other day, I left my car running overnight, and it started up again when I got in the morning. I took it for a short trip, and then, just five minutes after turning it off, it still wouldn't start. The voltage on the battery was 12.45 volts.

A second battery can be used to jumpstart the vehicle using the front jump ports.
Analysed voltage: 14.5 volts
Assuming the vehicle is not in sleep mode, the current draw is 70 milliamperes.
After removing the IBS sensor, the push-to-start function still does not work; the relay clicks audibly.

The following readings were recorded when the voltage under load and crank was measured directly from the battery in the boot:
turned off at 12.6 volts
1.25 volts for ignition and 12.2 volts for cranking

for measurements taken at the front jump ports
starting at 11.6 volts with a 0.4 volt cranking electrical system

When I tried to start it with jump leads after transferring the battery from the back boot to the engine block, I heard a clicking sound reminiscent of a machine gun.

I've heard that the positive cable that runs from the battery to the engine compartment is faulty. Conversely, I believe the automobile should have started because the battery was connected to the battery jump starters.

I'd be very grateful for any recommendations or suggestions for items to try.

Even though I enjoy a good puzzle, I am completely overwhelmed by this one. Though

[coolguy]

I should probably include the codes detected on the car as well. It seems like none of these are really important and are likely caused by the electricity not being distributed correctly to the car: The following information is displayed: ID, Status, and Description: | | 1A2002 | Intermittent| The electric fan may activate for a variety of reasons, including a short circuit to ground, an open circuit, a communication fault, an intermittent LIN message indicating that the alternator is missing, and an intermittent error code of 0DA451. We did not receive a communication regarding the real steering torque driver actuator 10.0.0.

When it came to the electric fan, I made sure it was spinning smoothly under load by turning on the air conditioner to full speed and other conditions. I also watched the fan activation percentage on the reader, and it moved up and down in sync with the reading.

[Black_raven]

There is either an issue with the earth or the positive connection between the battery and the jump point connector.
Where did you ground the multimeter lead when measuring at the jump point?

[coolguy]

Taking into account the positive leap and the left-hand engine bay earth point

It's getting dark and chilly, so I only checked the engine to chassis ground strap, but I also fear a poor connection between the rear battery and the engine bay. I also checked bad earths.

[Black_raven]

Since it drops to practically nothing while cranking under heavy load, there must be an issue with the main positive somewhere. Verify the location of the jumper wire where it ascends from the brake servo. Take off the scuttle trim piece.
Was the area in the boot where the positive cable from the battery joins to the one that travels to the front of the car examined? It's possible that it's corroded.

[coolguy]

Is there a way to test the cable to determine if it's bad? I noticed the bolted connection going through the battery well seemed dirty, but I cleaned it out. The cable on the engine bay side seems fine.

[heralder]

Ensure a secure connection at the jump point.

[Black_raven]

Actually, you won't be able to verify anything with a multimeter continuity test unless you happen to have one on hand.
The only thing you can do is check the voltage at the jumper connection; if it drops while cranking, the problem is further back. Poor connection between the main power wire and the jump point/starter cable has caused the jump point termination to shatter in the past.

[MDMH757]

Am I looking at the right battery? The local motor factor gave me a battery based on what their system indicated should be on there, which might sound foolish. It had trouble cranking when I returned it to Motor Factor, so they contacted the manufacturer, who informed them that my battery had a higher specification because it had all the possible extras. Nothing has gone wrong with the new battery; it appears identical to the old one, but it has a hundred more CCA.
You risk damaging your alternator if you don't inform the ECU that you've installed a new battery.