Parasitic draw 2000 LS 3.9

Carl Smith

Carl Smith

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I've battled this on my LS since I bought it. Originally, it was as high as 4 amps. Pulling the interior light fuse reduced that to around 370 ma after the car sits an hour and goes to sleep. Still too high and still making my battery weak if its not driven in a day or so. Using the millivolt voltage drop fuse process the current draw is coming from one single fuse, #20, inside the car which is listed for: FEM, Cluster, DATC, Brake shift interlock, and REM. I tried pulling the individual fuses for the FEM & cluster to see if this changed the reading and it doesn't. I assume the brake shift interlock is what locks the shifter if the brake isn't depressed. I don't have any common bad FEM symptoms like dash lights out, headlights , etc What is the DATC ?
 
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DATC is the climate control.
s-l225-jpg.jpg


It could be the source. I'd start by unplugging the DCCV. It might be where the problem actually is.

4A @12V is 48 watts. That's enough that you should be able to find it by feeling around to see what is hot. I found a bad DDM on a Grand Marquis that way once. I could feel the heat through the door trim even. If you have (or have access to) a FLIR gun, it should be really easy to find.
 
I left that connected and let the car "sleep" for over an hour and it stays dead on 320 ma. I unplugged the DATC and the ashtray/ seat heater connections and no change there either.
 
I really think that you should be able to find it by the heat that it is putting out. Maybe start by feeling the FEM and the REM 1/2 hour after shutdown, with all fuses in.
 
joegr said:
I really think that you should be able to find it by the heat that it is putting out. Maybe start by feeling the FEM and the REM 1/2 hour after shutdown, with all fuses in.
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Where is the REM located ? I know where the FEM is. I also ran that DATC diagnostics and got these. The low battery code is obvious.

12-61: Solar Radiation Sensor Open Circuit or Short to Ground
16-76: Battery Voltage Out of Range
19-67: Driver Heater Core Discharge Temperature Sensor Short Circuit
24-29: Passenger Heater Core Discharge Temperature Sensor Short Circuit
 
B1967 and B2429 are interesting. You might unplug those sensors and see if the codes change to open circuit. B1261 is more common and doesn't seem to cause much issue. Does autolamp work?

The REM is in the trunk, behind the trunk light. Note that it controls power to most of the car, so unplugging it won't really prove that it is the problem.
 
Just found the issue. I connected the meter in series with the battery this time and let her sit 2 hours. Showed the normal 300+ ma draw. I then felt the FEM and REM and they felt normal and not even warm. I then started fumbling around the FEM's connectors making sure they were secure and all that..go back and look at the meter and it showed 60 ma ! Looks like maybe a loose connector or pin or something. I will take it out and check for anything weird and maybe some electrical spray cleaning.
 
One issue remains though. Went for a test drive making sure to use everything in the car to do a retest that the issue remained gone and my overhead lamps front and rear never time out and shut off..no matter if the buttons are depressed or not. I tried them both ways.
 
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I assume you mean overhead, and I assume this applies to the footwell lights too. That's odd because I thought that even with a door open, the interior lights would go out when moving more than a few MPH. Maybe I am thinking of another car...
Anyway, either your FEM has a fault, or one or more connections to it are still bad.
 
joegr said:
I assume you mean overhead, and I assume this applies to the footwell lights too. That's odd because I thought that even with a door open, the interior lights would go out when moving more than a few MPH. Maybe I am thinking of another car...
Anyway, either your FEM has a fault, or one or more connections to it are still bad.
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You know, I will check the connections but I may get both modules rebuilt anyway. I would guess after 20 years capacitors and such start showing some age.
 
After the test drive activating everything electrical I can think of as well I reconnected the meter in series and I forgot last test to take the keys out and lock the doors. Doing that this time, with the fuse out to kill the overhead lamps, the draw went down to just 30 ma. I'll update later once I get the FEM out and the connections inspected and cleaned.
 
Forehead slapper...I had the dash light brightness level adjustment set all the way to high which was overriding normal overhead lamp operation. Backing that down a notch and they work normally now lol.
 
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So I pulled the FEM, REM, and PCM connections off, used electrical spray followed with compressed air, and replaced this melted junction that sits next to the FEM and she now drops to straight 0's when asleep. The replacement junction on the left is Gen 2 and exactly the same.

IMG_0923[1].jpg
 
joegr said:
The terminal must have been loose.
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It didn't appear so. The previous owner was the backyard redneck mechanic type who had wired up an electric cooling fan to one of the relays under the hood and somehow blew the PCM fuse. It sat two years before I bought it for that simple fix so it's hard to tell what caused that lol
 
Carl Smith said:
It didn't appear so. The previous owner was the backyard redneck mechanic type who had wired up an electric cooling fan to one of the relays under the hood and somehow blew the PCM fuse. It sat two years before I bought it for that simple fix so it's hard to tell what caused that lol
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Oh, that would explain it too.
 
Carl Smith said:
It didn't appear so. The previous owner was the backyard redneck mechanic type who had wired up an electric cooling fan to one of the relays under the hood and somehow blew the PCM fuse. It sat two years before I bought it for that simple fix so it's hard to tell what caused that lol
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Those wheels compliment your LS nicely...Kudos Mr. Smith
 
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