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E36 (1991 - 1999)
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Old 05-04-2020, 02:22 AM
supra-raleigh supra-raleigh is offline
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No Crank And Fuse 31 For OBC Keeps Blowing

I also posted this in the M3 forum. The car is a 95 M3 5spd, with a red DME and EWS delete chip.

After getting the car started and letting it idle for 30 minutes, I turned it off and connected the battery charger to the battery. I then cleaned up the ground points by the driver side headlight and the one by the under hood diagnostic port. I then removed the ground strap that connects the frame to the engine (the one from my previous post). I let the car sit like this for 2 days with the battery charging and the aftermarket alarm engaged.

I cleaned up the ground strap with a wire brush and some electrical contact cleaner and wrapped it with electrical tape. I then reinstalled the ground strap and tried to start the car. I got no crank at all. The interior dome light does not dim when I rotate the key to the start position.

Also, I noticed that the 3 lights on the small circular buttons for the climate control for a/c, recirculate and heat were blinking rapidly when the key is in the run and start postitions.

I also noticed that the on board computer was not illuminating at all. I checked the fuses and fuse number 31 was blown. This fuse is for the OBC - On-board and outside temperature displays. It worked fine until now. I replaced the fuse and tried to start the car. I got no crank and the on board display did not illuminate. I checked fuse 31 and it blew the new fuse.


My test light illuminates brightly while on the big wire on the starter. Battery voltage is 12.4 to 12.6V
Why is this fuse blowing?
Is this fuse 31 causing the no crank?
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  #2  
Old 05-04-2020, 06:07 AM
supra-raleigh supra-raleigh is offline
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I disconnected the heater control valve 3 prong connector by the dip stick and installed a new 5 amp fuse for F31. This caused my aftermarket alarm to sound so I clicked my key fob and disarmed the alarm. I then checked the fuse and it was blown. It blew and the key was not even in the ignition.

I read another post (from silver36) that says fuse 31 is always hot. The post also says fuse 31 controls the following:

1. Air conditioning
2. Clock
3. Instrument Cluster
4. On-board and outside temperature displays
5. Warning signal

JDStrickland posted that fuse 31 is for:

Central Locking
Driveaway Protection
Heating and A/C
Multi Function Clock
On Board Computer
On Board Display
Starting System

Looking at these lists, I am suspecting the OBC or clock as causing the fuse to blow because they are always drawing some current to maintain memory.

What are your thoughts?
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Old 05-04-2020, 06:29 PM
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dc_wright dc_wright is offline
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If you have the 18 button OBC it has an added security feature that allows you to set a 4 digit code. When you go to start the car, the ECU asks the ECU if the code has been set or not. The OBC either responds with the code or responds no code. If the ECU doesn't get a response it assumes the OBC has been tampered with and inhibits starting.
Short story - if you have the 18 button OBC it has to have power for the car to start,

How do I know this? Had this issue on my E36 due to a faulty heater control valve. It was causing fuse 31 to blow which removed power from the OBC.
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Old 05-04-2020, 09:22 PM
supra-raleigh supra-raleigh is offline
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No crank check fuse 31

Thanks for the response.

We got it!

It was the OBC. I never set a code for it. I removed it and it smelled burned. Sure enough the mother board had a nickel size round blue capatitor that burned the plastic cover attached to it. The mother board was also contaminated at the base of the capacitor.

I put another fuse in and the car cranks now.

Now, I'm back to where I started 5 years ago and still tying to nail down my hard start condition. I have a whole other post for that.

Last edited by supra-raleigh; 05-04-2020 at 09:23 PM.
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Old 05-05-2020, 08:01 PM
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Quote:
Originally Posted by supra-raleigh View Post
Thanks for the response.

We got it!

It was the OBC. I never set a code for it. I removed it and it smelled burned. Sure enough the mother board had a nickel size round blue capatitor that burned the plastic cover attached to it. The mother board was also contaminated at the base of the capacitor.

I put another fuse in and the car cranks now.

Now, I'm back to where I started 5 years ago and still tying to nail down my hard start condition. I have a whole other post for that.
It doesn't matter if you ever set the security code or not. When you turn the ignition to the start position, the ECU queries the OBC if the code's been set or not and looks for a CODE or NO CODE response.
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Old 05-05-2020, 08:54 PM
supra-raleigh supra-raleigh is offline
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The car starts now but again it still has the hard start condition. The OBC is removed.

Should I try another OBC as see if that solves the hard start?

Could it really be this simple?

Thanks for the help.

Last edited by supra-raleigh; 05-05-2020 at 09:01 PM.
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Old 05-06-2020, 05:41 PM
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The OBC issue is usually all or nothing. It either cranks over or you get nothing.
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Old 05-12-2020, 03:20 AM
supra-raleigh supra-raleigh is offline
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Smile

The hard start issue is finally resolved.

The problem was that the final step for the EWS bypass was not done.

The final step is to splice wires #1 and #3 together. I instead accomplished the final step by placing a jumper wire on the disconnected yellow EWS connector on the #1 and #3 female ports.

I left it disconnected and the car fires right up every time.

I am wondering if it is okay to leave the connector disconnected or if I should have spliced the wires together and reconnected the connector. If you know, please chime in.

Last edited by supra-raleigh; 05-12-2020 at 03:22 AM.
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