EF3 fuse keeps blowing. What's the most likely culprit? E39 528i 2000 (M52TU)

[jasontaylor7]

A fuse in my 528i keeps blowing. But, it controls so much stuff, I don't want to go on a wild goose chase. Please help me know what to check first.

This EF3 fuse is rated for 20 amps. It is located in the infamous "Motor Sicherungen" E-fuse-box:




(I say infamous because this box is nearly impossible to open without breaking a locking tab. It's ok though because there are two other tiny locking tabs which are more than enough to hold it together.)

Anyway, the middle fuse is the EF3 fuse. But, the truth is that the fuse isn't labelled within the car. I am just getting the name from https://www.bimmerfest.com/forums//s...4&postcount=90 . Speaking of which, this fuse allegedly powers the following items:

1. Cam sensors
2. Mass air flow sensor
3. Crank Sensor
4. Heated O2 sensors


There is also this mysterious-to-me note on that post:

"some say it's 30A, others say 25A - E-box fan, Transmission RPM sensor, CPS, MAF sensor, Fuel pump relay, SAP relay, A/C Compressor relay, Fuel tank leakage diagnostic module, SMG selector lever"

The 20A fuse blows if I turn the car on. (Before I attempt any cranking.) Honestly, I am a little shocked BMW has this much going on a single fuse. Horrible engineering!!!! GM would never do this IMO.

What should I check first? One note: the car was running fine, but failed to start up, with this fuse starting to blow on the hottest day of the year thus far.

Any suggestions or advice would be greatly appreciated! Especially this extra note which I don't understand. Is it saying on some cars that's what the fuse powers, or is it saying that the O2 sensors are on the curcuit with the fuel tank et al.

[M5XTu]

You have a shorted O2 heating element. Change the O2


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[JimLev]

A fuse in my 528i keeps blowing. But, it controls so much stuff, I don't want to go on a wild goose chase. Please help me know what to check first.

This EF3 fuse is rated for 20 amps. It is located in the infamous "Motor Sicherungen" E-fuse-box:


1. Cam sensors
2. Mass air flow sensor
3. Crank Sensor
4. Heated O2 sensors

Honestly, I am a little shocked BMW has this much going on a single fuse. Horrible engineering!!!! GM would never do this IMO.

You must have a direct short to chassis ground somewhere. Unplug the items one at a time.
What did you do to the car prior to the fuse blowing?

That's not a lot of items. 1, 2, and 3 hardly draw any current.
#4 is only on for a few minutes at most, all 4 O2's only draw 10 amps max.

[M5XTu]

Disconnect the O2 sensor and put a multimeter on both white wires. You should get an ohm reading (I believe 4ohms). If you get 0ohm, that’s a short.


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[Spirit Force]

Every make does this. Otherwise there would be million fuses in our cars. You can check everything that is it powering by checking WDS. That fuse powers multiple things. I took a quick look at WDS and it powers cam sensor 1, cam sensor 2, MAF, Crank sensor and thermostat (there was even more stuff but didn't check it all). As Jim said there must be short somewhere, unplug one at a time and check with multimeter.

[jasontaylor7]

You must have a direct short to chassis ground somewhere. Unplug the items one at a time.

Ok.

What did you do to the car prior to the fuse blowing?

Nothing. Just drove to the bank in hot weather. Get back into car, crank no start. Checked around and spend a few hours googling until I tested that this fuse was blown, and gets reblown just by turning on the car.

Thanks for the suggestions and comments Jim.

That's not a lot of items.

Well, some items are plural. #1, for example, is four O2 sensors alone. And if you consider items in the mysterious text, we are talking about ~20 different possible items, each of which can be hard to access. Oh, and did I mention, I've gone through all my spare 20 amp blade fuses already, and don't have fast access to transportation to the nearest store anymore since my main car is down. So, let's agree to disagree on that one.

[jasontaylor7]

Thanks for the suggestion M5XTu. The heating part of O2 sensors is basically like a light bulb, right? They have filaments, right? So, when they fail, they should fail open, not short. Right?

[jasontaylor7]

You can check everything that is it powering by checking WDS.

Thanks Spirit Force.

Sounds better than what I showed in my first post.

Is there a website you used to get the E39 wiring diagram that you don't mind sharing?

[M5XTu]

Thanks for the suggestion M5XTu. The heating part of O2 sensors is basically like a light bulb, right? They have filaments, right? So, when they fail, they should fail open, not short. Right?

That is correct.


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[edjack]

Try this site: https://www.newtis.info/tisv2/a/en/e39-528i-lim/

[JimLev]

Do you have an ohm meter?
If so put in on the lowest ohms range, R1 or X1, depends on the meter.
Hook one lead to a chassis ground, should be a post on the other side of the DME box.
Take to other lead and find out which one of the fuse blade recepticals is reading a short, near 0 ohms.
Now start disconnecting things until you find the meter sending goes up.

[jasontaylor7]

Try this site: https://www.newtis.info/tisv2/a/en/e39-528i-lim/

Thanks. I'm on that site. How would I learn which circuits use this fuse? I checked a random O2 sensor, but it was on a 30 amp fuse.

- - - Updated - - -

Do you have an ohm meter?
If so put in on the lowest ohms range, R1 or X1, depends on the meter.
Hook one lead to a chassis ground, should be a post on the other side of the DME box.
Take to other lead and find out which one of the fuse blade recepticals is reading a short, near 0 ohms.
Now start disconnecting things until you find the meter sending goes up.

Thanks. Good idea since I'm out of fuses. The only problem is the disconnecting things part. I'm still hoping someone narrows down the scope. 20 things is too much for me.

[JimLev]

At some point BMW changed F3 to a 30 amp fuse, my '00 540 has one.
Maybe stick a 30 amp in and see if it blows??
I doubt there are 20 things connected to F3, don't believe everything you read on that other site. Lots of shooting from the hip over there.

If 20 things are too much you could always have it towed to a shop I guess.

DME_Fuses_2.JPG

[jasontaylor7]

At some point BMW changed F3 to a 30 amp fuse, my '00 540 has one.
Maybe stick a 30 amp in and see if it blows??
I doubt there are 20 things connected to F3, don't believe everything you read on that other site. Lots of shooting from the hip over there.

If 20 things are too much you could always have it towed to a shop I guess.

The fuse is called F3? I thought the F3 fuse is in the cabin:

https://www.newtis.info/tisv2/a/en/e39-528i-lim/UxgaI2H

It's not 20 things. It's 20 possible things because I don't have a solid wiring diagram and the mystery parenthetical includes a ton of other parts.

[JimLev]

Lots of different fuse boxes in an E39.
Start disconnecting things, start with the O2 connectors just below the valve cover.

[Spirit Force]

Thanks Spirit Force.

Sounds better than what I showed in my first post.

Is there a website you used to get the E39 wiring diagram that you don't mind sharing?

I've tried newtis.info, but I find it a bit lagging for our cars. One of the issues is that can't select per ECU which wiring diagram is used. Some cars got 30A fuse, yours has 20. I use the latest WDS (2007). I got in a virtual machine so I can easily put in any computers I need. Once got it on the computer just clicking a shortcut on the desktop starts the virtual machine and the WDS. Sound more complicated than it is. Also got TIS on the same virtual machine. Do as Jimlev suggested use multimeter to find what is causing the short or near short. Start disconnectingthe things I listed in previous post, I checked those on WDS. As I said tjere is more stuff too, but you can start with those. If none of those are the culprit then take another look at the wiring diagram.

[jasontaylor7]

I think I found the problem. It was none of the sensors. It is the wires going to the crankshaft sensor (near vanos), which were underneath the intake manifold. (I had taken it off a few weeks back.) Yesterday's hot weather helped melt the plastic and foam enough that it put hot power to the block.

[M5XTu]

I think I found the problem. It was none of the sensors. It is the wires going to the crankshaft sensor (near vanos), which were underneath the intake manifold. (I had taken it off a few weeks back.) Yesterday's hot weather helped melt the plastic and foam enough that it put hot power to the block.

Glad you found the issue.


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[jasontaylor7]

IMG_0388-wire.jpg

[JimLev]

IMG_0388-wire.jpg

Looks like they were pinched.....that's why I asked you what you had last done to the car.
Good that you found it, cheap fix.

[jasontaylor7]

Looks like they were pinched.....that's why I asked you what you had last done to the car.
Good that you found it, cheap fix.

Well, the last job I did was described here: https://www.bimmerforums.com/forum/s...8#post30266658 It's not related.

Looking at my records, it was actually over a month ago that I did the under intake manifold heater hose repair.

Thank you Jim, M5, Spirit, and Ed Jack for your help.

[Spirit Force]

Good that you found the issue quite quickly. For once easy & cheap fix.

[jasontaylor7]

Good that you found the issue quite quickly. For once easy & cheap fix.

Well cost is subjective, but IMO this was an extremely expensive repair for me. I lost more than a day from work. I regret not towing it to the dealer. They have the wiring diagram I needed and it would have cost less in labor, which for me is very high/hour. I wasted several hours researching things while waiting for clearer replies to my post since the advice included checking the O2s, and that logic didn't work to well for me for reasons I pointed out even though I ended up checking four of them. I perhaps should have subscribed to alldata or something. It wasn't a nightmare repair, but guessing games are not pleasant. This car just isn't pleasant to repair. IMO it's stuffed full of obvious pro-dealer/anti-DIY booby traps, but mostly GTF (guaranteed to fail) tech.

[JimLev]

A 20+ year old car is always going to need repairs. What are you going to do when the tranny craps out?
With the limited info you gave us we did our best. It's free advice that didn't cost you any $$.
If you bought a Bentleys manual you'd have all the info about it as well as the wiring diagrams.
Another pointer....always go back and look at the last thing you worked on. That would have saved you some time.

[jasontaylor7]

If you bought a Bentleys manual you'd have all the info about it as well as the wiring diagrams.

I did buy one. But, I must have gotten ripped off. It's missing that section:
image manual 1 Snap32.jpg

image manual 2 Snap32.jpg

It's free advice that didn't cost you any $$.

Well again I'd disagree. I think it took ~5 people's time. And myself, it took time for me to research so that the question was legit. Our time isn't free at all IMO. But then we're all different, and I don't know your situation. Some people probably "enjoy" hanging out here or claim to enjoy it but have hidden incentives, but I'm not one of those people. I mostly come here to learn how to fix my e39.