Need Help--Electrical/starting problem

[srmmmm]

I agree with the battery isolator as number one suspect, but isn't there an "explosive" disconnect device on the positive cable terminal that severs the high amperage connection to the battery in the event of a severe collision or rollover? Might it be possible some corrosion has developed internally in that?

2002 X5 3.0 303,700 miles
2014 428i 19,000 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - Undergoing restoration

[upallnight]

Originally Posted by wpoll

Given the stated facts - 12v on the battery and no volts at the jump terminals under the hood (bonnet) - the only credible theory is that something is wrong with your battery isolator, despite the appearance that its ok. Or there really is a break in the main cable (very unlikely).

Checking the input and output on the battery isolator switch next time the fault occurs will be very telling...

Or the positive cable with the bst connector.

https://www.youtube.com/watch?v=c26Jq1O1m0M

[wpoll]

Originally Posted by upallnight

Or the positive cable with the bst connector.

https://www.youtube.com/watch?v=c26Jq1O1m0M

Agreed - although we ALL have these and I don't recall anyone have one become intermittent. Very few of us have added an isolator switch.

But yeah, one of these things...

BTW, I'm guessing you won't want to be anywhere near a BST when it goes off - and not just because the airbags have probably deployed at the same time!

[David.X5]

To Semcoinc- yes that is the part. Yes, works for every key. It attaches to the back of the keyed part of the cylinder. Find some instructions on removing the steering column trim (pretty easy) then disconnect the plug and 1-2 more screws and your done. It's so cheap and easy I wouldn't wait very long if you have that no-start problem. Could be something more serious, but given the age of our E53s, these sorts of parts will need replacing soon anyway.

Check the BMW part sources (ECS tuning, Fairfax BMW parts, etc) That's about the same price I remember paying for a genuine part.

[Pekelicious]

I'm facing the same problem with my 4.6, but all the light are lit but no start and no crank, i have to keep trying until it decides to start.... i had the same issue with my e39 i changed the ignition switch and that went away(knock on wood) already placed an order for a new I.S

[StephenVA]

These switches will drive you nuts looking for the issues as each circuit fails to energize a new "issue" appears. Based on the cost and effort to replace...just do it.

[g300d]

Originally Posted by bcredliner

I have an intermittent starting problem. Sometimes it starts fine. Sometimes I will get just a click like a dead battery. I can shut it off and start it immediately after that and it starts fine. Once in a while there isn't even a click and none of the dash lights come on. I have jump started it twice. First time it ran until I reved it and then it died. I jumped it again, drove it 4 miles with no issue and got home, turned it off and it started fine.

What I have done so far:

This started with a dead battery. Battery was bad. So was first replacement.
I have the correct and good battery installed
Checked for corrosion at front and back battery cable connections.
Turned on air on max and bright lights when it was running- alternator adjusted.
Monitored the alternator for spikes or dropping below min spec--no issue.
Let it sit for 8 hours checked battery status, no drain.
When it won't start there is no voltage under the hood but voltage at the battery is normal. Right now it is reading the same voltage at the battery and under the hood.

I do have a battery cut off switch but I can't make it malfunction. If I can make it happen again I will check if there is voltable on both sides. I am using a multimeter for testing voltage. I am aware electronics are sensitive and jumped it properly.

Any idea what troubleshooting I can do or what the problem might be?

Had similar situations in different vehicles over the years (not the X-yet), it was usually the starter.

ETA except for the no power to other components. IIRC I saw a similar situation here or on another BMW forum, a faulty ignition switch can cause similar symptoms.

[semcoinc]

Originally Posted by David.X5

To Semcoinc- yes that is the part. Yes, works for every key. It attaches to the back of the keyed part of the cylinder. Find some instructions on removing the steering column trim (pretty easy) then disconnect the plug and 1-2 more screws and your done. It's so cheap and easy I wouldn't wait very long if you have that no-start problem. Could be something more serious, but given the age of our E53s, these sorts of parts will need replacing soon anyway.

Check the BMW part sources (ECS tuning, Fairfax BMW parts, etc) That's about the same price I remember paying for a genuine part.

Thanks for the insight David. I will buy the I.S. and replace. I like to preemptively replace known troublesome components before they fail.

Mike

[Pekelicious]

My I.S Just arrived and I just picked it up....
The damage below( not suitable for people with heart problems 😹&#128569....



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[David.X5]

$365 USD ? Why so much. BMW Fairfax is asking $76 which is more than I paid last year

Update: Sorry, just noticed "Angola". Must be hard to keep a BMW going with import costs like that