still battery drain after rear sam replaced
Thread Starter
Super Member
Joined: Jun 2018
Posts: 533
Likes: 39
From: Northern Hemisphere - Chicago
fleet
still battery drain after rear sam replaced
2001 s430 with 160k miles, no issues ever till now
Battery Drain Overnight – Rear SAM Replaced, Still No Power after sitting drains battery
Hey everyone, I'm dealing with a persistent battery drain issue. If I leave the car parked overnight, by morning it's completely dead—nothing powers on at all.
--I read that the rear SAM could be the culprit, so I replaced it with a used unit. (I "diagnosed" the old sam by pulling a fuse and voltage dropped?) But maybe used part is bad too?
--I’ve also messed with the PSE before—tried swapping in a different unit, but it didn’t power on, so I just left the original one plugged in. my door locks and trunk dont work
At this point, I’m wondering if I should hook up a scanner and look for open circuit errors? maybe thats a thing?
Honestly, I’m at a loss. The only idea I have left is to take it to the dealership and pay their $250/hour diagnostic fee. Not ideal, but I’m running out of options. maybe someone has an idea here thats more reasonable than the standard copy paste stuff i post below
__________________________________________________ __________________
Battery Drain Overnight – Rear SAM Replaced, Still No Power after sitting drains battery
Hey everyone, I'm dealing with a persistent battery drain issue. If I leave the car parked overnight, by morning it's completely dead—nothing powers on at all.
--I read that the rear SAM could be the culprit, so I replaced it with a used unit. (I "diagnosed" the old sam by pulling a fuse and voltage dropped?) But maybe used part is bad too?
--I’ve also messed with the PSE before—tried swapping in a different unit, but it didn’t power on, so I just left the original one plugged in. my door locks and trunk dont work
At this point, I’m wondering if I should hook up a scanner and look for open circuit errors? maybe thats a thing?
Honestly, I’m at a loss. The only idea I have left is to take it to the dealership and pay their $250/hour diagnostic fee. Not ideal, but I’m running out of options. maybe someone has an idea here thats more reasonable than the standard copy paste stuff i post below
__________________________________________________ __________________
Common Culprits to Check
- Rear SAM (Signal Acquisition Module): Since you've replaced it with a used unit, it's possible the replacement is faulty or not coded correctly. SAMs can cause drain if they stay awake due to a communication fault.
- PSE (Pneumatic System Equipment): If the unit isn’t powering on properly, it could be stuck in a fault state or drawing current abnormally. Leaving it plugged in might be contributing to the drain.
- Aftermarket accessories or wiring mods: Anything added to the car (dash cams, stereos, alarms) can cause unexpected draw.
- Door/trunk modules or switches: If a door or trunk sensor isn’t registering closed, modules may stay awake overnight.
🧪 Diagnostic Steps You Can Try
- Use a multimeter to measure parasitic draw: Connect it in series with the battery and check current draw after the car goes to sleep (usually 30–60 minutes). Anything over ~50mA is suspect.
- Pull fuses one by one: If you see a drop in current when a specific fuse is pulled, that circuit may be the culprit.
- Scan for fault codes: A scanner can help identify modules that aren’t sleeping or have communication errors. Look for CAN bus faults or modules that fail to enter sleep mode.
🛠️ If You’re Stuck
- Independent shop with Mercedes experience: Might be cheaper than the dealership and still have STAR diagnostic tools.
- Dealership route: Painful at $250/hr, but they’ll have the right tools to scan every module and check sleep cycles.
Last edited by e350forme; Oct 9, 2025 at 12:27 PM.
MBWorld Fanatic!
Joined: Dec 2012
Posts: 2,473
Likes: 439
From: Ball Ground, GA (N of Atlanta)
2003 S500 2007 GL450
Remove the CD from COMAND.
Research the system that is the equivalent of GM's ONSTAR (calls home if there is an accident, or you can push the red button near the rearview mirror). Pull fuses and disconnect the entire system.
https://ricksfreeautorepairadvice.co...ry-drain-test/
Remember that some modules take a long time to actually go to sleep, so you have to do things like not opening a door or the trunk to do the testing.
Research the system that is the equivalent of GM's ONSTAR (calls home if there is an accident, or you can push the red button near the rearview mirror). Pull fuses and disconnect the entire system.
https://ricksfreeautorepairadvice.co...ry-drain-test/
Remember that some modules take a long time to actually go to sleep, so you have to do things like not opening a door or the trunk to do the testing.
Member
Joined: Dec 2021
Posts: 179
Likes: 30
From: Nyc
S-600 w220, Nissan s13 coupe, and Nissan s13 convertible
Buy a remote battery cutoff switch 12v off of Amazon. $60 for a 320amp. Disconnect the battery with the remote after you've locked the car. Problem solved
Thread Starter
Super Member
Joined: Jun 2018
Posts: 533
Likes: 39
From: Northern Hemisphere - Chicago
fleet
i tried but sometimes battery still died with the remote version. the physical knob disconnect is what i am using now. car in storage , in spring i will try the method of pulling fuses with the meter inline for resistance is my understanding.
my command cd is missing but that is an excellent tip to disconnect fuses
my command cd is missing but that is an excellent tip to disconnect fuses
Member
Joined: Dec 2021
Posts: 179
Likes: 30
From: Nyc
S-600 w220, Nissan s13 coupe, and Nissan s13 convertible
The remote one shouldn't drain that mich battery. You probably need a new battery. Idk if its the alarm of what but the battery dies after about 3 days. I havent had that problem since I installed the remote cutoff. I wish the clock would keep the time. I gotta reprogram the automatic close for the windows, but its better than looking for a jump all the time. Grab a new battery and try the remote cutoff again. Good luck with your car
Thread Starter
Super Member
Joined: Jun 2018
Posts: 533
Likes: 39
From: Northern Hemisphere - Chicago
fleet
The remote one shouldn't drain that mich battery. You probably need a new battery. Idk if its the alarm of what but the battery dies after about 3 days. I havent had that problem since I installed the remote cutoff. I wish the clock would keep the time. I gotta reprogram the automatic close for the windows, but its better than looking for a jump all the time. Grab a new battery and try the remote cutoff again. Good luck with your car
now that i think about it. is there any car problem that would cause batteries to go back? like fry them? technically i am on the second battery in 5 years. so basically, it would charge but then not hold the load on the load charger. it was just weird that 2 batteries went out.
