winner!

i ended up replacing the k40 relay and it has resolved my problem. it's strange since i replaced the k40 only a few years ago with a genuine mercedes replacement. i guess it's just a poor design that's prone to failure. might have to start keeping a spare one in the trunk.

i get gp light now, engine starts and runs perfectly now, and the obd2 port is also working properly now. all issues are resolved upon replacing this k40 relay.

the old one was definitely clicking when you turned the key, so something inside it was working. curious, i popped open the old one to have a look. inside is a circuit board with three separate relays mounted to it. one of them must have failed, or a solder joint must have overheated and cracked. whatever the problem, it isn't immediately obvious to me, nothing looks burnt, but clearly this k40 is the culprit.

thanks everyone for the help, i'm back on the road.

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The new K40 relays have the same problem as the old K40 relay, namely too little solder used on all the pins. Eventually you're going to have to reflow all the joint and add more solder.

The way to fix the GP light is to take apart the GP relay and solder new wires onto the 2 signal pins. GP relay with the old ****ty plug still attached. Mine had at least a couple of MM of play. You can slide it up and down by hand.


I took apart the relay and soldered the black and white wires onto the pins inside the relay. These plug into the original wiring harness with some standard crimp on connectors. No more intermittent GP light.

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