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Marty
Marty, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 53943
Experience:  Bosch Certified Master Technician with over 35 years experience in the automotive industry.
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I have a 2001 slk200. It has suffered from starting problems.

Resolved Question:

I have a 2001 slk200. It has suffered from starting problems. I suspected the starter and renewed it. Problem still existed. Then I fitted new battery, problem still exists. Checked and remade battery to chassis and chassis to engine earths. Looking on forums suspected K40 relay. This has been inspected looks very clean, all soldered joints sound and all fuses OK. Believed battery may be dropping below 12.6 volts when car laid up and locked with immobiliser on so been leaving unlocked and on charge. Today 3 days after re-use the car failed to start. Had loud clicking noise. Battery voltage is 12.95volts when engine not running and about 14.8 volts when engine running. Disconnecting the battery, leaving for about 10 minutes seems to clear the problem. Any ideas what the fault may be? Any help would be appreciated
Submitted: 1 year ago.
Category: Mercedes
Expert:  Marty replied 1 year ago.
You need to test the voltage to the starter solenoid when it won't start. If you have 12V at the small wire when turning the key to the start position you simply have a defective starter. If you do not have 12V I would replace the K40 relay. It's not always easy to spot a bad solder joint on in the relay.Let me know if you have any questions.Marty
Customer: replied 1 year ago.
Don't believe there is a starter solenoid on the starter. Think main 12v positive cable runs from K40 relay and the solenoid function is contained within K40 relay. Can check if getting 12v at starter when key turned. As fault has cleared by disconnecting and reconnecting battery it is liable to be ok. If it is then perhaps I should check this when fault reoccurs. Thanks
Expert:  Marty replied 1 year ago.
Yes there is a starter solenoid on the starter. The K40 closes the starter relay and the relay sends 12V to the starter solenoid.
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