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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 11-17-2013, 11:01 PM   #1
bdailey
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Smile 2001 E46 330Ci Convertible, cranks only when jumped (FIXED)

FIXED! This is what I got. 2001 E46 330ci convertible. Background (not sure if related but I think it is)- Installing amp – in the final stages putting it all back together and the power lead on amp disconnects and hits negative lead to amp quick spark but no fuses popped on lead going to battery. Put it all back together, amp works fine, listening to stereo while I put rest of car together and repair the door lock, about 2hrs. Go to start car, get little clicking sound, but nothing. All lights and stereo work fine. Figure I must have drained battery; jump the car from the post in engine compartment, starts right up. Go pick up kid, back in 20 min. Turn car off, try to restart, will not crank. Later – jump car again, go for a 3-hour drive at night, lights and everything work fine. Turn off car (thinking the battery must be charged), will not crank. Put trickle charger on overnight, in morning will not crank. Run BMW battery test, 12.4 volts. Use voltmeter, same results. Clean contacts, check battery positive cable master 250 amp fuse all good, no crank. Buy new battery, does not crank. Hook old battery directly to (+/-) posts in engine compartment of car, car cranks. Volts at post in front of car 12.4 volts. Volts in trunk 12.2, Alternator 14.2 volts.

Is there a fuse I am missing somewhere? Are there other grounds that I need to check? I have tired different keys (thinking may a fob issue since I was messing with locks), but it just does not make sense that the car will start fine when I connect the battery to the post in the engine compartment but not in the trunk. Is there a relay or something that is before the positive post in the engine but after the positive post in the trunk? I disconnected battery and touched +/- together (supposed to reset) nothing. Now I have disconnected battery and will leave disconnected overnight to reset any computers. Any help will be appreciated. I have read and searched for hours and have run out of things to try. I do not think it is the battery (new battery and old battery starts car when hooked to post in engine compartment), starter (starts fine when jumped), alternator (lights and everything ran for 3 hours). Seems I am bypassing something when I hook battery to posts in engine compartment.

Last edited by bdailey; 11-23-2013 at 07:56 PM. Reason: FIXED!
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Old 11-17-2013, 11:24 PM   #2
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Are you sure it has nothing to do with the amps? tried cranking with those disconnected?
I would check for battery voltage at the starter and trace it from there.
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Old 11-17-2013, 11:52 PM   #3
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I know the video I just watched said the car would still start if the BST was tripped but that really makes absolutely zero sense. I would check that first. The positive terminal on the battery has a a huge connection on it. See if the large power wire coming out of it jiggles around. If it does, you tripped your BST. That huge cable goes directly to the starter. Without it, the starter has no power.
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Old 11-18-2013, 12:44 AM   #4
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Thanks for the fast response. i will check both those tomorrow. Researching the BST - I did not hear it go, the cable seems pretty solid. I searched for a battery wire diagram but could not find. So the really thick red wire goes to the started and the skinner on goes to the engine compartment?
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Old 11-18-2013, 04:33 AM   #5
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The smaller wire powers everything in the car. It doesn't go to that terminal under the hood - if that's what you were asking. That terminal also goes directly to the starter.

If your alternator is at 14.2 while the rest of the car is only at battery voltage, I really can't see it being anything other than a tripped BST because the alternator charges the system through that large wire. Those are the only things connected to it. When the engine is off - the alternator is reading 0V right? Because it should be reading battery voltage.
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Old 11-18-2013, 11:06 PM   #6
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BST seems to be fine - and I am getting 12.4 volts at the posit in the engine compartment, and wire is solid.
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Old 11-18-2013, 11:24 PM   #7
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you might want to do a load test on the battery I work on motorcycles and we have batteries stored on the shelf for a while they rear 12v but when loaded a lot of them drop to 10 and under thus not starting the car just an idea
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Old 11-19-2013, 11:30 PM   #8
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Ok - did a load test, showed the new battery was weak - got my hopes up, charged the battery and .... no crank. Sorry my post are so slow - working all day and only little time at night. Tonight I ran the jumper cables from the back to the front +/- posts in the engine compartment. It started right up! So now I will check the neg ground and continuity on the positive line. I have examined the BST - and it seems fine. I did notice that I only have 11.5 volts when I check the positive line up front. Searching for an electrical diagram that lines out from the battery to the starter.
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Old 11-20-2013, 12:24 AM   #9
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Have you measured the resistance across the BST? That is the only way to check it. If you jump from the back to the front and get the car to work, your cable isn't doing the job.
And have you checked the engine ground cable for connectivity?
Positive cable runs from the battery thru the pass compartment and out into the drug bin terminal. Then connects over across the top of the engine to the starter motor. Then another cable takes it from there to the back of the alternator.
You've got a relatively easy problem to solve here. Do u understand the path I've described above?
See the diagram here for some clues as to what I've described above.

Last edited by Stinger9; 12-14-2013 at 03:31 PM.
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Old 11-21-2013, 12:16 AM   #10
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Thanks for the help and the pictures - this is what I found out tonight. It is the positive cable. I ran a negative jumper from the back to the front - no start. I ran a positive jumper from the back to the front and it started. Here is where it gets complicated. I did a power check using a circuit tester on both sides of the BST - power on both sides. I did load test in the engine compartment and got 12volts while static, zero volts under a load. Looking like the BST. Looking at a BST diagram, seems like it would be all or nothing - either you have a connection or you do not. Why would I get 12volts static (there is continuity) and zero volts under a load? Looking at the pics of blown BST - the silver metal coupling shows from under the black plastic part. Mine looks fine and brand new. Shouldn’t I have airbag lights if I have a blown BST? Maybe I am in denial.
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Old 11-21-2013, 12:54 AM   #11
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Easy to get a no-load 12v on a digital voltmeter. Might even have from capacitance or backfeeding from the accessory line.

Did you measure the resistance across the BST with the + cable removed from the battery? Second time I asked you this.
You need the kit to replace the BST.
Forget overthinking how it may affect other things.
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Old 11-21-2013, 02:28 AM   #12
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Searched how to measure the resistance resistance across the BST - could not figure how. I assume to mean remove the plastic cover from the BST and test the resistance the couple of inches from the end of the terminal to the other side of the bst. 1.6 on the 200 ohm scale.
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Old 11-21-2013, 04:32 AM   #13
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The BST cables are known to have problems, the cable has a end that is press fit inside the BST connection. You could try to grab the cable at the output of the BST and see if you can twist it easily, it should not twist or be able to be pulled back and forth.

Checking the resistance of the BST will be hard, you can easily do a Voltage drop check on the BST if you use a Voltmeter, but you may have a problem getting the Voltmeter connection on the engine side of the BST cable.

Negative Voltmeter connection on the battery, positive Voltmeter connection on the engine side of the BST connection, you may have to pierce the insulation on the BST cable on the engine side with the probe tip or use a razor knife to put a tiny slit in the cable insulation? You may still get 12 Volts when you measure with no load, but then have someone try to start the engine and you should see the Voltage drop way off, maybe even to zero if the BST connection is bad.

Be careful working around the BST cable as I have no idea if what happens if there is a loose connection inside and it arcs with the BST propellant. I am guessing it is not a huge explosion, but at least wear goggles or safety glasses just in case.

Good luck.

I think I have heard of people actually reseating the BST connection by twisting and pushing the engine side of the cable back into the BST at least for a short period of use?
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Old 11-21-2013, 12:10 PM   #14
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Quote:
Originally Posted by jfoj View Post

Checking the resistance of the BST will be hard, you can easily do a Voltage drop check on the BST if you use a Voltmeter, but you may have a problem getting the Voltmeter connection on the engine side of the BST cable.

Negative Voltmeter connection on the battery, positive Voltmeter connection on the engine side of the BST connection, you may have to pierce the insulation on the BST cable on the engine side with the probe tip or use a razor knife to put a tiny slit in the cable insulation?
To measure resistance of BST, suggest alternatively using a pin to pierce the cable for minimal invasion. Alternatively you could extend your test lead with a piece of wire to measure at the positive terminal in the drug bin.
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Old 11-21-2013, 03:48 PM   #15
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Check the connection at the firewall. The cable from the jumper terminal leads to it.
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Old 11-21-2013, 05:20 PM   #16
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So the resistance ended up bing 1.6 on the 200 ohm scale measuring from the batt terminal (disconnected) to the other side of the BST. What does that mean?
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Old 11-21-2013, 05:37 PM   #17
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That would mean that the BST is OK. But did you twist and fiddle with it when measuring to make sure the connection wasn't intermittent?
Internally the contact may be only tenuous.
Do you have a lower Ohm range you could use?
No 20 Ohm scale or even less? Are you sure you measured 1.6 Ohm. That would be practically zero on your scale.
Digital or analog meter?

Tell us where you measured from on the engine side of the BST? Did you pierce the cable with something sharp?

Last edited by Stinger9; 11-21-2013 at 06:12 PM.
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Old 11-22-2013, 12:25 AM   #18
bdailey
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Ok - Thanks for all the suggestions - keep them coming. I do not think it is the BST. I removed the plastic cover, visual inspection - looks ok, grabbed both ends not loose, did a resistance check on BST (disconnected from battery, post side to bare cable on fitting) 1.6 ohm on the 200 ohm scale (lowest my digital multi tester will go). Did a load test on battery - good load 12v. Connected BST to battery did a load check first by connecting load meter to the fitting on the battery post - 12v good load. Then did a battery test test by connecting to the cable side of the BST - 12v good load. Car still does not crank. Went to engine compartment - 11v on posts in the drug bin and 0v under a load - car does not crank. Ran jumper from + post of battery to + post in drug bin - started. So something between the cable in the trunk and where it comes out the firewall in the + post in the drug bin. Will pull out the back seats this weekend to see if I did something when I installed the speakers and put the seats back in. Will check the cable connections in drug bin tomorrow, any other thoughts?

Last edited by bdailey; 11-22-2013 at 02:51 PM.
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Old 11-22-2013, 09:16 PM   #19
Stinger9
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The battery cable route is not rocket science. A simple cable all along the way. So if you jump around it and the car works, then the cable is open somewhere. Most likely the BST. Would have to melt somewhere along the way to be anything else.

Last edited by Stinger9; 12-14-2013 at 03:32 PM.
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Old 11-23-2013, 08:11 AM   #20
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Make sure the connection at the drug bin it good as well. If the bolt is loose you may have an issue there.

Measuring resistance on the BST is not really a valid test, yes a resistance test is valid, however, under the type of load that a battery capable of putting on a connection, there may be a very different situation. If you can load test the BST, just measure Voltage with no load and then under load and this will answer the question very easily. Anyone more than 0.2 Volt drop is out of range and is a problem.

Not likely that the battery cable has an issue inside the cabin, it probably has issues at the end connections.
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