Hallo All,

I hope someone can help me with this weird problem.
2008 gl320

The car was park for more than 6 months. Before park, the car was working fine. I have an other ml that I use and decided to park GL and I have tickle charger on. Before parking the car, the main battery and Aux battery were replaced with new one and drive the car for a month before insurance expired and parked the car. I did start the car few times in the last 6 months and it started right up. Few weeks ago friend came by and was looking at the car and open the car door. Right when he opened the door the car alarm went . Note that I didn't locked the door more than 6 months and he opened the door without using the key in fact the key is still some where in the house. So I ran inside to grab the key and try to unlock the the car but the alarm still on and I even start the car but did not turn off the alarm. When I decided to remove the battery cable, the alarm turn off. Tested the battery all 12.4 including the aux battery. So i Ignore since I am not planning to drive the car anyway so I keep the tickle charge on and the door unlocked for few weeks.

This week I decided to use the car again. So go to the car open the door ( door still unlocked) put the key in ignition, turn the key, I got a message, door open, vehicle not in park and beeping sound from cluster. Anyway, I started the car and it start right up and beeping sound and message still there. I tried to change the gear nothing work. Pull the scanner and read the code, I got A80 ism. The car was fine before I parked. Car still on and try to think what could that be. Went under the car and try to see if any wiring damage cause by mouse or animal but nothing. Checked the voltage all charging and over 12.volt.
Shutdown the car after warm up and decided to remove the ground aux battery that attached to main battery. Started the car, The first error didn't appear but the white battery error show up and I could shift the gear and move the car. At this point I assume the Aux battery is malfunction. Tested the aux battery and still get 12.3 volt. Plug aux battery ground back, turn the ignition key and I got the first error and couldn't change any gear. Removed the aux ground, I could shift the gear.

Next I decided to pull the main battery, aux battery and checked. I found nothing wrong with Battery. So put everything back and the first error still there, removed ground I could shift the gear. So for the 3rd time I decided to remove battery, Aux battery and this time I removed front sam to checked water damage and found nothing inside and clean and dry. At this point I decided the swap my Aux battery with the old aux battery which full charge and read 12.2 volt. Put everything back, turn the ignition, start the car and I can't shift the gear. Disconnect the ground for Aux battery, I could shift the gear.
Back to square one. Both Aux battery are Mercedes benz. I even swap the battery from my ML still same thing.

I run all the test front sam, rear sam and found no error except A80.

If anyone ever seen this problem please let me know what the solution.
If this is ISM, why would it work when I disconnect the aux ground ? At this point I could drive the car when I disconnect the Aux battery.

Thank you for reading.

 

Disconnect all batteries, walk away for a day, and write a much shorter gripe next time if that doesn’t work.

 

lol

Do you ever get the feeling all these one time symptoms guys are mechanics trying to troubleshoot a customer's vehicle?

I wonder if the batteries got tired of being tickled.

 

Seems like your batteries are quite low on voltage.

 

Hallo,

I am not mechanic but I do work on my own car.
Removed the battery over night and still something.; Can't move the gear when aux battery connected.
My tickle charger only run 3hr per day because I had timer on it.
I swapped the battery with my ML and still doing something.
I run data stream on my ML to compare the result with GL and I found something odd with GL ISM. I think i am going toward replacement of ISM.
Does anyone know Vancouver area can program used ISM ?

 

Are you sure your trinket charger isn't draining the batteries? They should be 12.6.

Get a good battery maintainer - they're only $20 - on the main and then the aux battery. Try it after a day on each, or when the maintainer's light turns green.

Trickle chargers can easily ruin batteries. You really want one that is designed to monitor the battery's state of charge and adjust accordingly.

P.S. Don't take it personally - we get guys here all the time who write up massive diagnostic posts and overlook the simple. I'll never forget my car guy friend who bumped the battery terminal, discovering it's loose, and barked at me, "It's always the simple stuff!" Sure, sometimes it's not; sometimes it's big stuff, but always always always rule out the simple stuff first.

 

Hallo sorry I have not have time to deal with this until last week and Nothing take personally.

So I ordered new ISM and Installed it in the car then the car running normal. It has been week and it is all working like it should be. Knocking on the wood.

I still don't get it why it ISM broken when it was sitting for a while.

In my case, if anyone have ISM problem and can't move the car or shift the gear, try to disconnect the AUX battery cable that go to negative battery. Maybe you can drive the car to flat bed instead of dragging the car to flat bed. The car drive and shift fine without connecting the AUX battery in my case but when I connect the AUX battery, it will not shift out of park. Scan the code and still point to ism. Still mystery but I am happy after replacing ism it is work normal so problem solved.

 

Hallo sorry I have not have time to deal with this until last week and Nothing take personally.

So I ordered new ISM and Installed it in the car then the car running normal. It has been week and it is all working like it should be. Knocking on the wood.

I still don't get it why it ISM broken when it was sitting for a while.

In my case, if anyone have ISM problem and can't move the car or shift the gear, try to disconnect the AUX battery cable that go to negative battery. Maybe you can drive the car to flat bed instead of dragging the car to flat bed. The car drive and shift fine without connecting the AUX battery in my case but when I connect the AUX battery, it will not shift out of park. Scan the code and still point to ism. Still mystery but I am happy after replacing ism it is work normal so problem solved.