Just got my GLS450 back from the dealership after warranty work. Mileage at 46k, so I asked for a price quote on changing spark plugs (will be due at 50k). Price came back at $545. Not surprising...

What did surprise me was the note on the quote: PLEASE NOTE ENGINE WIRING HARNESS MAY ALSO NEED REPLACING FOR SPARK PLUG JOB TO BE SUCCESSFULLY COMPLETED, DEPENDING ON CONDITION OF HARNESS."

I asked my SA about the note, and he said "Oh, this engine has a known issue with the wiring harnesses; they often disintegrate during the spark plug job."

Normally, this wouldn't bother me, since my car is still under warranty... what do I care if they have to replace the wiring harness, right?

EXCEPT, I was toying with the idea of replacing the spark plugs myself, as an opportunity to teach my teen son some basic under-the-hood skills. Grrrr...

Anyone else with the 450 engine had a wiring harness replaced?

Thanks... (and please forgive my double-posting from the GLS forum. I figured there are a lot of GLE450 owners out there too, with the same chassis and engine)

 

Yikes. I'm guessing they didn't put proper heat shielding over the wires that run close to the exhaust then?

 

Sounds like a BS dealer money grab. Fire that dealer and go elsewhere.

 

UPDATE: I just got my GLS450 back from the dealership after spark plug replacement.

They also replaced (under warranty):

- ENGINE WIRING HARNESS 256-150-60-00
- CONNECTOR (x2) 256-159-08-00

The technician notes stated: "Wire harness causing misfire; Found wiring to be cracking." And two spark plug connectors apparently disintegrated while doing the job.

Glad I didn't find that out the hard way, in my garage on a Saturday...

 

hmmmm, not good.

 

Although totally embarrassing to MB, I am wondering if shielding the exposed wires at the end of the harness connecting the coils would hold them up longer.
Given the cause of integration is thermal stiffening of the wires; would that be a viable solution ?
I’ll try it on my CLS 450 and see if the harness holds up, a good foam spray should do the job.

 

Worth the preventative measures for sure.

 

I had my front connector wires starting to wear away the wire coating. Just be careful with them and if they have signs of that, just put liquid electrical tape on them. That seemed to work fine. I think it's the heat from the engine that get's them really hot and the wire coating start to disintegrate.