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DaddyGlenn's Avatar
 
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Location: Pittsburgh
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2000 e38 (740iL) battery drains overnight

Not expecting a lot of help here, unless Shogun stops by. But here is my issue...

2000 e38 (740iL) battery drains overnight.

Alternator has been ruled out and the battery is new.

Before I start methodical fuse pulling, are there any usual suspects I should check?
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Glenn
Daily Driver - '78 911SC RoW, Track - '85.1 944
Wife's - '00 740iL (Sport),
Support vehicle - '00 Suburban 2500 4x4
Son's - '85.1 944
Old 12-08-2017, 03:34 AM
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Sorry, have not been here for a while, Glenn.
If the battery drains overnight, that must be a lot. Normal for the E38 is 50 mA.
But there is no other way than checking. Maximum closed current by vehicle
E31 50mA
E32 50mA
E34 40mA
E36 30mA
E38 50mA
E39 40mA
E46 40mA
E52 50mA
E53 40mA
Z3 30mA

Performing Closed Current Draw Test
• Select proper measuring device (DISplus, MoDic or DVOM)
-Remember amperage draw in excess of 10A will damage DVOM.
-Use inductive amp probe of DISplus when amperage draw is high.
-When using DISplus inductive probe, clamp on negative battery cable with arrow pointing away from battery. Switch off all consumers. (It is not necessary to disconnect B- from body when using inductive probe). Connect (-) test lead to negative battery terminal and (+) test lead to a known good ground.. Ensure all systems are OFF !
Be sure DVOM is on and set in proper mode.
Disconnect battery ground lead from body.
Observe meter reading, wait for vehicle to enter sleep mode.
Identify faulty circuit by disconnecting fuses, relays, control modules or connectors, observing meter readings. Defective circuit is found when current is below maximum closed current for vehicle being tested.

use this link for more details http://www.e38.org/battery.pdf
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Old 12-25-2017, 04:48 AM
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Thanks for the response, Shogun.

I finally had time to start isolating the problem.

In sleep mode, I was seeing 550mA. I went through all the fuses in the trunk. Found a couple that set of the alarm when pulled, forcing me to have to reset and wait for sleep mode again. Ultimately, I did not find the offending circuit in the rear fuse block.

Moved to the fuses in the engine compartment. Pulled all the smaller fuses that are easy to get to under the flip cover and still nothing. So I removed the four 5mm screws holding the larger cover to get at the big fuses. The last one I pulled (50A fuse, #78) caused the current draw to drop to 30mA.

Reference materials indicate Fuse #78 protects the "Engine cooling fan" circuit.

Now to find where the problem is in that circuit. First thought is a faulty relay. There has got to be a relay, right? Looked it up in my Bentley manual and it turns out there are three. And all of them live behind the glove compartment.

Next step is to pull the glove compartment and have a look. But this is making sense. I did have a leak from an old, cracked seal at the bottom of the windshield that resulted in water leaking in behind the glove compartment. So, perhaps some water got to the relays and caused a bit of corrosion. We shall see.
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Glenn
Daily Driver - '78 911SC RoW, Track - '85.1 944
Wife's - '00 740iL (Sport),
Support vehicle - '00 Suburban 2500 4x4
Son's - '85.1 944
Old 12-30-2017, 12:30 PM
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Update

Well, I should have looked at the Bentley manual more closely. Those three relays I was looking for behind the glove compartment don't exist on later model e38's like mine.

It turns out that the cooling fan is controlled by the ECM and there is no relay between the ECM and the fan.

So that means either:
  1. The ECM is sending a minimal signal to the fan
  2. There is a short in the wire between the fuse and the fan or
  3. There is a fault in the fan

I doubt it is #1. I'm hoping for #2 with an easy fix. But I fear it will be #3, which will be expensive.

Stay tuned...
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Glenn
Daily Driver - '78 911SC RoW, Track - '85.1 944
Wife's - '00 740iL (Sport),
Support vehicle - '00 Suburban 2500 4x4
Son's - '85.1 944

Last edited by DaddyGlenn; 02-05-2018 at 03:32 PM..
Old 12-30-2017, 03:44 PM
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Just to close this out. It turned out to be the fan. Replacing the fan was easy and solved that problem. Now on to the 1,000 other issues with this car.
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Glenn
Daily Driver - '78 911SC RoW, Track - '85.1 944
Wife's - '00 740iL (Sport),
Support vehicle - '00 Suburban 2500 4x4
Son's - '85.1 944
Old 02-05-2018, 03:34 PM
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