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A few days ago I decided to go ahead and order a New aftermarket ISM from a seller on eBay. I know I’m taking a huge gamble and it probably won’t work, but he promised he’d take it back if it didn’t work so I decided what the hey. I’ll try it. Getting the ISM removed without doing the transmission is an absolute nightmare.
I had a floor jack and stands, so I did the job on my back with just inches between my nose and the bottom of the transmission. There is barely an inch between the ism and the body of the car and I had to use a mirror to see the top bolts. I ended up making my own tool, which believe it or not actually worked at getting the top bolts loose, but ended up getting a smaller ratchet at Harbor Freight the next day to make line easier.
If the new aftermarket ISM doesn’t work then I’ll find a used OE example and have it reprogrammed. I’ll know Monday night or Tuesday when it arrives. Might as well replace the transmission mount while I’m at it. Makeshift tool New aftermarket ISM
So before that long tow to the dealer, double-check those dash lights and make sure the wagon's actually malfunctioning - it's not uncommon for those fancy computer systems to throw codes for no apparent reason. Also, if you're running some aftermarket mods, those might be causing the issues - worth a thought.
So before that long tow to the dealer, double-check those dash lights and make sure the wagon's actually malfunctioning - it's not uncommon for those fancy computer systems to throw codes for no apparent reason. Also, if you're running some aftermarket mods, those might be causing the issues - worth a thought.
Alex….. Do yourself a favor and read the entire thread post-by-post, then read your reply again.
or you’re a god-tier troll in which case you got me lol
Congrats: two thumbs up on graduating the ISM module removal - This takes some serious doing...
Now that you have ISM removed you should inspect the harness connector and the module side for signs of water crusties. Feel free to waterproof the harness connector back end so water does not follow wires through the loose seals.
Swapping a used donor unit is now going to produce a different set of results. If your unit was failed, the donor may network better with CAN-C but then fail the "drive authorization" security.
I think there is 0% chance donor is going to fly without getting a security massage to match your car.
Shortcut: you won't need to reinstall neither genuine/donor ISM to test functions are operating PRND shaft output. So long its attached to harness and perhaps grounded case.
Having removed ISM offline you will see if this helps resolve your other existing issues ?? - Obviously partners modules are going to complain of missing ISM, which can be ignored for CAN testing purposes.
Connecting and disconnecting ISM should be done with batteries offline so CGW can recognize module status upon powering up. Clear faults afterwards.
Let me know how I can help your besides sharing you may want to open up your ISM for its missing grease job + serious soldering of the oxidized pins. Then it should be lifetime.
++++ I think there are online services that can transfer coding from your old to a donor ISM.
Last edited by CaliBenzDriver; Mar 13, 2026 at 03:09 AM.
When my ISM died (there is a thread about it) the behavior was identical to the OP. What a PITA. Plus, getting the AMG on the tow truck (with no wheels turning) caused about $1500 in damage.
Congrats: two thumbs up on graduating the ISM module removal - This takes some serious doing...
Now that you have ISM removed you should inspect the harness connector and the module side for signs of water crusties. Feel free to waterproof the harness connector back end so water does not follow wires through the loose seals.
Swapping a used donor unit is now going to produce a different set of results. If your unit was failed, the donor may network better with CAN-C but then fail the "drive authorization" security.
I think there is 0% chance donor is going to fly without getting a security massage to match your car.
Shortcut: you won't need to reinstall neither genuine/donor ISM to test functions are operating PRND shaft output. So long its attached to harness and perhaps grounded case.
Having removed ISM offline you will see if this helps resolve your other existing issues ?? - Obviously partners modules are going to complain of missing ISM, which can be ignored for CAN testing purposes.
Connecting and disconnecting ISM should be done with batteries offline so CGW can recognize module status upon powering up. Clear faults afterwards.
Let me know how I can help your besides sharing you may want to open up your ISM for its missing grease job + serious soldering of the oxidized pins. Then it should be lifetime.
++++ I think there are online services that can transfer coding from your old to a donor ISM.
Thank you, sir. I appreciate that! I just received the new ISM in the mail this morning and put it onto this line and tighten the two lower torque bolts since the two top ones are a complete pain, and I don’t want to install them unless I know this new ISM will work. I’m charging up the battery separately outside of my vehicle as we speak so I can start the car with a full charge.
Any other suggestions before I get started here?
Just FYI, the ISM I just installed is a new aftermarket unit, not used, so there shouldn’t be any programming to be erased or the need to be “virginized”. The reviews of this exact one are 50-50 on Amazon, so fingers crossed. The brand is “LDGSUPH” from China.
If this doesn’t work, then I’ll find a secondhand unit and send that off to be programmed to my vehicle
Also, here’s a scan of my vehicle with no ISM installed…
When my ISM died (there is a thread about it) the behavior was identical to the OP. What a PITA. Plus, getting the AMG on the tow truck (with no wheels turning) caused about $1500 in damage.
did they mess up your differential? Also what did it cost you from the dealership all in for the ISM replacement?
This is an extremely good news :
New ISM running without SCN coding
now back driving again!
ISM is a security part Mercedes does not retail to anyone without a professional licence. Price through the roof!
"Drive authorization" is linked to ISM with enrolled keyfob security.
This simply working is noteworthy: great!
Thank you sir for your support and words of affirmation! The car is all back together now and driving like a dream.
I’ll have to start looking into the engine cooling fan issue and address the faulty intake manifold, but now that I have a creader scan tool, it should make things much easier.
I’d also like more info on refurbishing my original ISM just in case the replacement doesn’t last. They seem to be sealed with some sort of compound that needs to be melted off. I know it won’t be easy
Thank you sir for your support and words of affirmation! The car is all back together now and driving like a dream.
I’ll have to start looking into the engine cooling fan issue and address the faulty intake manifold, but now that I have a creader scan tool, it should make things much easier.
I’d also like more info on refurbishing my original ISM just in case the replacement doesn’t last. They seem to be sealed with some sort of compound that needs to be melted off. I know it won’t be easy
You can dig in your original ISM as time permite - Your new unit should last you long enough to not need another swap.
Your engine fan waking up to drain your battery is now a top concern. This is another tough one because fan works and dysfunction randomly... for unknown reason.
You can use your cReader to test the fan speed control.
> FAIL SAFE:
The oddity is fan needs a 10% pulse to stop spinning.
A 20% duty cycle spins it at 10% speed
What this sounds like is your fan is not getting its 10% pulse to stay Off, so it starts spinning.
You can dig in your original ISM as time permite - Your new unit should last you long enough to not need another swap.
Your engine fan waking up to drain your battery is now a top concern. This is another tough one because fan works and dysfunction randomly... for unknown reason.
You can use your cReader to test the fan speed control.
> FAIL SAFE:
The oddity is fan needs a 10% pulse to stop spinning.
A 20% duty cycle spins it at 10% speed
What this sounds like is your fan is not getting its 10% pulse to stay Off, so it starts spinning.
Using the CReader, I performed a test of the engine cooling fan and 10% increments and everything seems to be functioning correctly. The only faults are from one or two different interior temperature sensors.
However, I do notice sometimes that when I open the drivers door the fan will kick on sometimes for only a second or two. This. also seems to happen when the front passengers door is opened as well. I know this isn’t an uncommon issue and I’ve seen certain instances where it’s an internal issue in the ECM.
The issue was somewhat resolved by adding a remote battery cut-off. This $30 unit from Amazon went bad just before I started having my list of issues, but the issues may have remedied by clearing all fault codes since I haven’t heard the fan going as much lately.
XxUsing the CReader, I performed a test of the engine cooling fan and 10% increments and everything seems to be functioning correctly. The only faults are from one or two different interior temperature sensors.
However, I do notice sometimes that when I open the drivers door the fan will kick on sometimes for only a second or two. This. also seems to happen when the front passengers door is opened as well. I know this isn’t an uncommon issue and I’ve seen certain instances where it’s an internal issue in the ECM.
The issue was somewhat resolved by adding a remote battery cut-off. This $30 unit from Amazon went bad just before I started having my list of issues, but the issues may have remedied by clearing all fault codes since I haven’t heard the fan going as much lately.
You picked up an interesing clue: fan starts spinning when any front doors gets opened.
Actually that means "when chassis wakes up from sleep".
A truly bad fan will spin regardless of sleeping or not because FAN is always powered up but set to sleep mode.
Your fan passed preliminary testing with scanner.
Issue may be in between harness connections. Check if water got in on radiator connector.
OBVIOUSLY... NEVER HISE DOWN ENGINE BAY!!
Q: Does your fan stops when you stop the engine or does it keeps spinning alone??
Last edited by CaliBenzDriver; Mar 17, 2026 at 10:51 PM.
You picked up an interesing clue: fan starts spinning when any front doors gets opened.
Actually that means "when chassis wakes up from sleep".
A truly bad fan will spin regardless of sleeping or not because FAN is always powered up but set to sleep mode.
Your fan passed preliminary testing with scanner.
Issue may be in between harness connections. Check if water got in on radiator connector.
OBVIOUSLY... NEVER HISE DOWN ENGINE BAY!!
Q: Does your fan stops when you stop the engine or does it keeps spinning alone??
that’s the strange thing sometimes it will turn off the engine and others won’t, and sometimes it starts while I lock the car It will go for a few seconds or it will keep going for five minutes. It’s kind of random and sometimes which is the worst part, it will just start up on the car is locked until the battery dies.
And definitely agree never to hose down for power wash these in bay. I only clean it with a wet rag to get dust off.
that’s the strange thing sometimes it will turn off the engine and others won’t, and sometimes it starts while I lock the car It will go for a few seconds or it will keep going for five minutes. It’s kind of random and sometimes which is the worst part, it will just start up on the car is locked until the battery dies.
And definitely agree never to hose down for power wash these in bay. I only clean it with a wet rag to get dust off.
Very interesting account details!!
> GOT IT!:
With these details and all the work you've done prior...: 90% chance the fan circuit board needs attention or cleaning.
> WHY...
-- Fan gets prefuse all time power + awake power + PWM signal command.
-- How: when ECU stops PWM fan signal, it removes +12V to command fan sleep.
-- Fan spinning during chassis sleep means its ignoring command to sleep (lack of +12v signal).
You now got this issue pinned down!
> FAN REPAIR ??
-- Inspect fan connector for signs of oxidation.
-- See if you can disassemble your fan to access its control electronic board. It'll be interesting to see how water got in to bridge narrow gaps or leaky aged capacitors
else new/used fan to hopefully/likely have problem fixed.
> NEXT...
Are you running out of fault to have yourself a trouble free MB ??
You can focus on normal maintenance & disabling voltage drama (CTEK / ALT-LIN).
Last edited by CaliBenzDriver; Mar 19, 2026 at 05:48 PM.
UPDATE: after driving from Plano (Dallas) to Lake Jackson (Houston) and back there were zero issues with the ISM, direct select, transmission, etc. all seem to be working flawlessly after repairs.
Last edited by johnfranciscog; Mar 23, 2026 at 04:37 AM.
> GOT IT!:
With these details and all the work you've done prior...: 90% chance the fan circuit board needs attention or cleaning.
> WHY...
-- Fan gets prefuse all time power + awake power + PWM signal command.
-- How: when ECU stops PWM fan signal, it removes +12V to command fan sleep.
-- Fan spinning during chassis sleep means its ignoring command to sleep (lack of +12v signal).
You now got this issue pinned down!
> FAN REPAIR ??
-- Inspect fan connector for signs of oxidation.
-- See if you can disassemble your fan to access its control electronic board. It'll be interesting to see how water got in to bridge narrow gaps or leaky aged capacitors
else new/used fan to hopefully/likely have problem fixed.
> NEXT...
Are you running out of fault to have yourself a trouble free MB ??
You can focus on normal maintenance & disabling voltage drama (CTEK / ALT-LIN).
Maybe one day, perhaps. I still need to address the dynamic seat bladders as the tailgate issue but hopefully one day it will be fault-free
