2006 SL500. The reverse lights will not come on when car is started.
after 10-15 minutes they work normally. While they're not working, if I push the gear selector forward slightly, they work. Thoughts?

 

Does it show you are in "R" on the MFD in the instrument cluster?

 

Yes. Everything is normal except as described.

 

Strange. The reverse lights are controlled by the rear SAM, and it's communication from the shifter should be over the CAN bus, which would be the same signal the instrument cluster gets to show the current gear. But, I do see a single wire from the gear selector position sensor going into the rear SAM. Maybe this is some sort of backup signal? How about the gear selector position light on the shifter itself - does "R" light up on it? It;s ties into this same wiring harness.

I guess the possibilities here are a problem int he gearshift mechanism or int he rear SAM. If you have SDS, the rear SAM can be tested and reverse lights actuated.

 

MBZ tech scratched his head and mentioned something about a bushing in the shifting mechanism. another one concurred w/that but neither had seen this. oh well!

 

Wow, re-reading my post in your quote makes me realize how poor my typing skills have become!

It seems there is some redundancy here in reporting the selected gear. There is circuitry in the ESM (gearshift) to report the gear selected (PRND). There is also circuitry inside the transmission, on the conductor plate, tied into the integrated TCU, that detects and reports the gear (PRND). There is (obviously) a mechanic connection between the ESM and conductor plate (the shift linkage) and there is an adjustment in that connection. A bad bushing could put it out of position so that the ESM might not "quite be" in reverse, but the TCU is. Or that grub screw adjustment is loose and needs to be corrected. Maybe the reverse lights respond to the report from the ESM, but the ICM's (instrument cluster) indicator responds to the TCU? In that case, the transmission would be in reverse (the TCU controls that) and the ICM would report the correct gear, but the rear SAM would not be getting the signal to activate the reverse lights.

Just some thoughts...

 

Yes, but bear on mind that it is only defective for the first 10-15 minutes of cold operation. After that, there are no problems with the reverse lights for the remainder of that operation cycle (drive time) When the car is shut down and fully cooled off, it's back to no reverse lights for 10-15 minutes.

 

Maybe the linkage is just enough out of adjustment that the heat of operation expands it to set it right. Again, just throwing out SWAGs.

 

My 2 cents:

I have never experienced anything like that. But, what you're saying here makes me think it's a more mechanical problem than electric, if it responding to heat. Thus, the path you might wanna go is starting with the cheapest part in the chain that might fix the problem, if replaced. If it's that small plastic part that is a subject to wear and tear, you might wanna start there, and so on. At least that's what i'd do.

Regards

 

Here's how the shifter linkage is attached:

http://benzbits.com/r230/ShiftRodLinkage.pdf

A bad bushing at part #33 or #97 could cause enough slack so that the shifter isn't fully in reverse. If those are good, then you adjust this by removing the set screw #2 and then rotating the grub screw #99 so you can then lengthen or shorten the linkage.