CL55 AMG, CL65 AMG, CL63 AMG (C215, C216) 2000 - 2014 (Two Generations)

Key fob lights up but doesn’t unlock or start car

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Old Dec 6, 2021 | 08:07 PM
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Jiro San's Avatar
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Key fob lights up but doesn’t unlock or start car

Hey everyone,
I took the car off road to do some work and disconnected the battery.
Work done was: ABC filter and fluid change, all accumulators, seal kit for both valve blocks, radiator, spark plugs, SC surge tank gaskets, valve cover gaskets.
More work planned: IC pump, front lower ball joints, transmission fluid and filter, diff fluid, SC oil, maybe rear valve block again as rear has dropped while front is holding strong while parked for several months.

When some work was done I reconnected the battery and car turned on.
Then the battery drained because the trunk light was on so I removed the battery while I finished off remaining work on car.
I charged the battery outside the car and last week attempted to start the car. Connected battery and got power to lights etc but the key fob won’t lock or unlock doors/truck or even turn inside the ignition barrel.
I get dash lights and radio but nothing from key.

So far:
1. Checked key fob with camera and can see IR signal.
2. Key fob red light comes on when I press buttons.
3. Changed key fob battery.
4. Cleaned key fob circuit board, ignition barrel and shell with alcohol and electronics cleaner.
5. Checked all fuses and all good.
6. Tried turning the steering wheel and it turns a bit but makes no difference.
7. Tried the reset with putting key in ignition, pulling out and pressing lock/unlock buttons.


I read about brake switch and have that out on a bench trying to find a way to test it before ordering a new one.
Also, read about EIS and other high dollar parts that may have died.

Can anyone explain what’s going on? If the key fob looks and functions ok, is it the receiving end in the car that’s the problem?
I can even turn the key so can’t run any diagnostic.

Should I try a new car battery and branded key fob battery?
I’d really hate for it to start needing the signal receiver etc after all the work it’s had done so far…

Last edited by Jiro San; Dec 7, 2021 at 02:15 PM.
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