2010 Mercedes CLS 550 Will Not Start – Key In, Battery Charged, Starts After Waiting a While. What's Going On?

Hey garage crew,

I’m dealing with a weird intermittent no-start on my 2010 Mercedes-Benz CLS 550.

Symptoms:

• Battery is fully charged (tested good voltage).
• Key goes in and turns (or push-button start works).
• Sometimes the car does nothing when I try to start it — no crank, no click, dash lights are on normally.
• After sitting for a while (sometimes 10–30 minutes or longer), it suddenly starts fine like nothing was wrong.

It’s not every time, which makes it extra annoying. The car has been otherwise running okay when it does start.

I’ve heard this could be related to:

• Electronic Ignition Switch (EIS) module issues (common on these cars — solder joints or internal failure)
• Starter relay or a sticking relay
• Some kind of “Drive Authorization” module glitch
• Parasitic drain or a module not going fully to sleep
• Or possibly a weak connection somewhere that resets after time

Has anyone here run into this exact or similar problem on a CLS 550 (or other W219 CLS / W221 S-Class era Mercedes)?

Questions for you:

1. What fixed it for you? (EIS repair, relay replacement, module reset, etc.)
2. Did you need a Star Diagnosis / Xentry scan to pinpoint it?
3. Any temporary workarounds while diagnosing?
4. How expensive did the fix end up being?

I’ll update the thread with what I find once I dig deeper (planning to scan it soon). Photos of the dash or any error messages if they appear.

Real talk only — let’s help each other out with these German electrical gremlins.

Thanks! — David | What’s In Your Garage