Hi all,

I have a Mercedes-Benz CLK55 AMG (209.376) with the M113.987 engine.

The alternator recently failed while driving, which caused the battery to go flat and the car to shut off. After towing it home, I charged the battery and tried to restart the car. It cranks, but there is no spark.

What I’ve checked so far:

• Fuel: Present
  
• Air intake: Good
  
• Compression: Good
  
• Crankshaft position sensor (CPS): Replaced with no change
  
• Battery: Brand new, holds charge
  
• Spark plugs: Removed one and tested—no spark
  
• Error codes: None related to ignition in any system
  
• Fuses (front SAM): Inspected, all good
  
• Wiring: Looked over generally, no in-depth tracing yet
  

Since all spark plugs stopped working at once, it seems unlikely they all failed simultaneously. If just one coil had failed, I would expect the engine to start but misfire. This points to a system-wide electrical issue preventing spark.

Before the alternator failure, the car ran perfectly with no issues.

Current suspicion:

• Something may have triggered when the battery went flat—possibly the immobilizer/anti-theft system or another system that disables ignition.
  
• Tried multiple diagnostic tools but couldn’t perform special functions on the immobilizer system.
  
• Diagnostic readout shows:
  • Immobilizer = NOT ACTIVE
    
  • Start Enable = YES
    
  • Status of Drive Authorization = Immobilizer is Activated
    

This is confusing, because it suggests the immobilizer shouldn’t be blocking start, yet the status says it is activated.

What else could be preventing spark in this situation?

 

Dumb question, but did you replace the alternator?
John

 

Waiting for new unit. Also found problem, it was in fact the fuse for the coil packs when checking it all looked good, but i didnt bother testing each one properly and thats on me but that was the issue, car starts now normally.