drrick52

I hav3 a new to me sl 500. ‘05 model that has 106000 miles. I just replaced the abc pump and accumulators due to a bad hose ( replaced as well ). I was having fun with it but it failed to start last week , either with keyless or with key fob. Symptons are no starter sound and now clicks . When in position 2 the shifter moves and indicators show the range . The lights on dash are all on . The relay for starter in passenger fuse box feels like it closes when my wife turns the key on as if to start. I tapped the starter wth a pipe to no avail in the hopes I could see if it would kick over. All fuses appear good. I have a new brake switch to install but I fear the starter itself is the culprit. I plan to put on a lift and trigger the solenoid to the battery and see if it will engage before replacing the starter. Looks like a job I woul$ like to avoid. Any advice .?

thias

You do realize that your car has two batteries, do you?
It may be that your trunk battery is fine, hence all the lights come on. But your starter battery might still be bad.

pmercury

iTrader: (2)

lol

larry mack

had a similar issue. has your car gone into 'limp' mode? are you having issues shifting into park? does the console display the correct gear or is it blank?
my '05 e320 would not start, but battery was fine. the shift control module is bad. the car doesn't start because it doesn't know or can't tell which gear it is in.

seven_out

According to the OP's post this is an issue with the starter solenoid not engaging. The starter battery has no role in that; it simply turns the starter motor.

That relay may very well have worn contacts. Since you hear no "click" from the starter solenoid, if you are in Park or Neutral as Larry suggested, this seems to be the case.

To investigate I suggest that you measure the voltage on the solenoid while the relay is energized, or you remove the relay from the car, energize it with 12 VDC, and measure the resistance across its contacts. If you need detail for that procedure, just ask. Alternatively, measure the voltage on the starter solenoid while the relay is energized. If 12 VDC is not present, then the relay has failed; if it is, then the starter solenoid has failed.
.

larry mack

the main (big) battery is for starting. the AUX battery under the hood is mainly for SBC functions. when you get the RED battery warning light in the center display it's you AUX battery failing. replace it or risk losing your brake function. there is no "starter" battery.

seven_out

You've got that backwards, Larry. Except in the case where the key is in the ignition or the ignition is switched on via KeylessGo and the trunk battery is weak, the battery under the hood is connected to the armature of the starter motor and nothing else.

For example, when your car has been idle for a time, have you ever opened a door and heard the SBC pump run briefly? In this case power for the pump motor is supplied by the battery in the trunk.

larry mack

really? that little battery under the hood has enough cranking power to start a v6/v8. my understanding was it was for the SBC unit and what MB calls "convenience features." when mine started having issues i kept getting the brake warning message (not the failure message) and the reduced power convenience features disabled.

drrick52

I plan to energize the solenoid directly from the terminal to the positive battery r
terminal when I can get it up on the rack to see if it is the solenoid/start assembly. That would rule it out.
ihave ordered anew relay as the one in the car is green in color and not black like the others. May have been an issue before .

drrick52

My understanding of the battery layout is that the trunk battery feeds everything except the armature of the starter. In theory the rear battery could actually provide some help in starting if the front battery was weak S it charges the front battery in use. Is that not correct ?

drrick52

the dash shows the correct gears when shifting the gearshift so I assume the shift control module is OK

ray0214

Larry.. the battery under the hood is indeed the battery that powers the starter. SBC and all accessories are powered by the consumers battery in the trunk

seven_out

I'd say you are exactly right. In theory the rear battery can assist a weak front battery, but in practice this doesn not happen.

But there is a way to fakeout the battery control module and link a rear battery with a not terribly-weak front. You remove the negative battery cable from the rear battery, insert the ignition key, and within 30 seconds or so re-connect the rear battery and start the engine. Finally, you reconnect the negative cable to the rear battery.

drrick52

A final note. I was able to remove and replace the defective starter over the weekend . Was able to remove without the need to remove exhaust, or motor mount. Having a lift made it possible for sure. Was a tight space but with a bit of wiggling I could get it out and then back in .glad to have it back and running .