Hello everyone,

I'm reaching out for some help with my 2002 Mercedes G500 that's been giving me a hard time. Here's the backstory and what I've tried so far:

Background:

A few months ago, I left my G500 at a friend's place. His brother-in-law, who does mechanic work, was going to fix an issue with the electric auxiliary fan not powering on. He took apart some wires, including the front SAM module on the passenger side and some ignition components. Despite this, the car was still running and starting fine. He moved it to a parking spot where it's been sitting outside for a few months.

Life got busy for both of us, and unfortunately, the car just sat there—with the key left in the ignition the whole time. We've had a lot of Texas heat and a lot of rain over the summer, but the car was dry when I recently tried to start it.

Current Issues:

• Car Won't Start: When I turn the key, nothing happens. No cranking or ignition sounds.
• Key Fob Unresponsive: The remote won't lock or unlock the car.
  • Initially thought the key fob batteries were dead; replaced them but no change.
  • Noticed some battery corrosion dust around the key fob; cleaned it carefully with isopropyl alcohol.
  • The lock/unlock light on the key fob blinks as it should.
  • Tested the infrared signal with my phone camera—it appears to be working.
• In-Car Lock/Unlock Works: I can lock and unlock the car using the buttons inside.
• Hazard Lights Functioning: All blinkers work when I press the hazard light button.
• Replaced Car Battery: Installed a brand new battery but still no luck starting the car or getting the key fob to work.
• Key Fob Tested: Went to a key shop where they tested the key fob's RF and infrared signals; both are working fine.
  • The shop mentioned that Mercedes keys, even older models like mine, shouldn't lose their programming even if left without a battery for a while.

What I've Considered/Tried:

• SAM Module and Ignition Components: Since these were taken apart, I'm wondering if there's a connection issue.
• Key Synchronization: Not sure if the key needs to be resynchronized with the car.
• Immobilizer Issue: Could the immobilizer be preventing the car from starting?

Request for Help:

I'm somewhat handy and have done some work on the car before, so I'm willing to try troubleshooting steps myself. I'm also on a budget and can't afford high repair costs right now.

Could anyone please help me with:

• Diagnosing the Issue: Any ideas on what might be causing this problem?
• Troubleshooting Steps: Specific things I can check or try to get the car started.
• Guidance on SAM Module and Ignition: How to properly inspect and reconnect these components.
• Key Resynchronization: Is there a procedure to re-sync the key fob with the car?
• Additional Advice: Any other suggestions or insights would be greatly appreciated.

Thank you so much in advance for your time and assistance!

Any sign of rodents taking up residency?

Thanks for the reply! I have not directly correlated this but the car is sitting in a more rural area. My buddy has chickens and goats on the land but nothing inside the car. He also did mention that rodents can be found on his land from time to time and that it could be the culprit.

where would I start with inspecting for this? Also what fuses/relays would I need to check first?

is the information about the key fob not losing its programmed memory for the car true? It could have been without battery for 6-7 months max I’d say.

The first thing to do is look for evidence -- excrement and nesting material debris laying around on the ground and underneath the vehicle. Inspect the engine compartment and areas underneath, including under the skid plates. I had a mouse build a nest in my air filter box once, and my car was garaged. Just a week ago, I repaired a chewed-up headlight cable on my Jeep. If there's no evidence of rodents, consider yourself lucky -- replacement cable assemblies are very expensive to replace. If you continue to park outside and truck isn't being driven, put some mothball packets in the engine compartment and on the ground underneath. If there is rodent activity, damaged cables are usually easy to spot. If rodent damage isn't the problem, then you need to being tracing out the high current cabling from the battery to the starter.

If it sat outside for as long as you shared, then I'd also be sure to check the grounds.... living in Houston I found that often was an issue on my landcruiser that sat for a good bit...

I assume it has a fresh battery w/ clean connections ? TX heat is also brutal on batts....

There aren't many indy shops in Houston I know of who'd likely be able to run electrical quirks.... these guys did help out a friend on his 63 that was acting up.... but no frame of reference otherwise. https://www.thegaragisti.com/our-reviews

Maybe some other Houston peeps will have suggestions on other shops.....

Thanks again for the insight. I'll check these things to see the condition and if there is any evidence. Appreciate your help!

Yes fresh battery that was the second thing I tried after changing the key fob batteries but made no difference. Going to rule out the wiring and key fob first before taking it to a shop. The grounds is also a great idea and will add this to the list to check. Thanks for the insight!

Does any of the interior electronics power on when you turn to position 1 or 2? Windows, radio, etc?

Have you tested out the brake lights, headlights, fog lights, etc are functioning correctly? If they work correctly then your Front/Rear SAM modules are most likely not the issue since all lighting is controlled through them.

No crank when you turn the key - is there any clicking at all? Have you tried 'tapping' the starter when someone is turning the key?

You installed a new battery, but have you put a voltmeter on it to see what voltage it is actually at? Which battery did you purchase as a replacement?

Interior electronics power all work (stuff that does not require the key). Door locks and hazard lights. I will check the other items like brake lights next time I am there. No clicking at all with turning the key. Have not checked with voltmeter but I initially tried to use a strong jumpstarter to crank the car thinking the battery would have been dead from the get go. I am quite positive the battery I bought is good. But will confirm to cross it off the list. I think next steps are also to check for any sign of rodents nesting or chewing through wiring.

Good the battery is fresh - I'd grab a good Voltmeter and wirebrush plus dielectric grease for all your grounds and connections... what side of Houston are you on ?