Vehicle: 2018 Mercedes Benz GLC300 4MATIC (253.949), L4-2.0L Turbo (274.920), Automatic Transmission/Transaxle

Mileage: 55,429

Problem: The customer stated that when stopping, the engine will intermittently shut off and not restart when trying to accelerate from the stop. He must put the shifter back in Park and use the push button to restart it.

Case Details: The tech took the vehicle out for a test drive to verify the concern. What the tech noticed was that, with the ECO start/stop button in the ON position, the engine would shut off normally when coming to a stop. But when leaving the stop, it would try to restart 3-4 times and sometimes not restart. With the ECO start/stop system in the OFF position, there were no issues. The tech also noticed when he started the engine manually using the push button, the engine would crank about a half turn sometimes not start. If he kept pushing the button, the engine would eventually start.

He scanned all the modules for diagnostic trouble codes (DTCs). The only DTC he found in the ECM was: P1CE200 – The ECO Start/Stop Function Has Detected Excessively Low Engine Speed.

He began the diagnosis by checking the basics. He load-tested the battery and checked the battery terminals and grounds. Everything was in good condition. Next, he tried replacing the voltage converter module (passenger side axillary battery) since it was the original and had never been replaced. That didn’t solve the problem, so he reinstalled the original voltage converter module and decided to focus on the weird cranking issues. Remember, the tech had mentioned that the engine would crank over about a half turn and then start after repeated tries.

The tech inspected the starter motor and noticed that it was severely corroded and was making an odd sound when cranking.

Confirmed Repair: After installing a new starter, the engine would crank over and start normally with the push button, and the ECO Start/Stop feature also functioned as it should. The DTC was cleared and it did not return. Mystery solved!