MNTBIRD

2006 R350 - When turning key dash lights up but starter will not engage. checked fuses and starter relay all are good. Changed batteries in key fob still won't start. Battery replaced 3 months ago. Has been starting fine in the past.

Current DTC 903C "Component F58kH (Circuit 15 relay) is defective or missing, or the feed line has open circuit"

Any Help is appreciated.

DansGL

I had something very similar. Actually got stranded once. I changed the "Engine" relay in engine compartment. It was relay'D'. Not sure if it will help you but just swap out relay 'D' with the one beside it for "air pump" just to rule out the relay. If this doesn't help then download some good wiring diagrams.
Good luck fellow MB'er

Dan

https://mbworld.org/forums/gl-class-...-resolved.html

MNTBIRD

Thanks Dan!

After spending several hours with a Mercedes mechanic on Just Answer the problem is resolved.

Turns out that the "circuit 15" relay had no ground due to a faulty fuse box. This is the relay right next to the starter relay. I simply bent the ground lead of the relay up towards the case and clipped a lead to the lug and to a ground point on the body. Car starts and runs fine now. Not pretty but functional.

Guess I need to replace or repair the ground path in the fuse box

Anyone have experience on sourcing a new fuse box and/or How To on doing this?