Battery Drain Insight: Fuse "C" (16-A) and Fuse "9" (8-A)

[M104-AMG]

While this is for the C36-powered S124 wagon, I believe Fuse "C' and Fuse "9" are similar in both wagon & sedans.
Moderators - please move as necessary.

In short, I've narrowed down a 3+ amps battery drain to the following fuses: "C" and "9.

Before I go opening up the fuse-box and remove/test each lead for each circuit, based-upon the below functions, does anyone have any experience with those functions, esp. in Fuse C ? That is, what could be pulling 3+ amps ?

Thanks,
neil
==========
Per the fuse-designation card (124.545.13.00):

Fuse 9 (0.75-amp draw @ rest):
Diagnostic terminal. 6; hazard warning system; clock; front roof light; radio, vanity mirror light; relay comfort circuity terminal 86

Fuse C: (3-amp draw @ rest):
Rear roof light; trunk light; rear door locking system; safety belt handover arm (n/a); seat back arrester; central locking system; door lights; reading lamps; aux. antenna; control unit seat adjustment

 

[M104-AMG]

It's definitely Fuse "C", as I needed to wait even longer for "rest time" (30-secs vs 10-secs), and only remove ONE fuse at a time.

Fuse C: 3+ amps for 20-seconds (when battery ground disconnected & then reconnected), then settles to 0.86-amps draw after 1-minute of observation;

Fuse 9: 0-amp draw after 1-minutes of observation (will fluctuate between 1.2 & 0.8 amps when Fuse C is drawing 3+ amps, but then settles down to 0-amp draw after 45-seconds.

In short, I have just shy of a 1-amp continuous drain on Fuse "C", whose functions are:
Rear roof light; trunk light; rear door locking system; safety belt handover arm (n/a); seat back arrester (n/a); central locking system (most likely the 3+ amps for 20-secs when battery disconnected/reconnected); door lights; reading lamps (n/a) ; aux. antenna; control unit seat adjustment

Car stereo amps have their own circuit and fuse to battery, as I installed a separate fuse/power distribution block for aftermarket items with positive and negative feeds fused.

Neil

 

[darek_u]

My wild guess:
9 draws 10W, for 400/500E my first choice would be diagnostic socket pins are corroded and current is leaking there. Mirror lights are off for sure? They have 10W bulbs.
C draws 40W, I would rather exclude lights. Antenna maybe? It draws 3A when motor is running...

 

[darek_u]

Aaaah disregard what i wrote, I was typing while you were posting more details. The 3A draw when battery is reconnected is coming from antenna I think - it wants to retract by default when power is applied if memory serves me well. Can you hear it after 20 secs?

 

[DerFuror]

I've encountered a current draw anomaly attributed to fuse #9 & long periods of garage storage. I keep the car on a trickle charger. About 2-3 years ago towards the end of annual Winter storage, I noticed the charger's LED illuminating red instead of the normal green. Nothing initially obvious until I turned the garage lights off. I noticed some of the gear shift & center console indicator lights were illuminated. The current draw was eliminated by pulling fuse #9.

Interestingly, the current draw went away once I started driving the car regularly. Everything functioned normally. No draw while parked.

The same thing happened during this past year's Winter storage, so I pulled the fuse again until drive time. The draw has once again disappeared now that I'm driving the car (I just walked out to the garage to verify no changes).

I'll have to dig up the notes from my original investigation which tell exactly which lights were illuminated, etc. I will eventually further troubleshoot when time allows. It hasn't become overly annoying yet.

The bottom-line is I need to drive more often.

 

[jhodg5ck]

Any weird draw on an 036 I Immediately go check the diag port under side condition..


I'd unplug your door light switches just to rule them out. Seen them do Dumb things.

 

[rayhennig]

I believe Fuse "C' and Fuse "9" are similar in both wagon & sedans.
Moderators - please move as necessary.

In short, I've narrowed down a 3+ amps battery drain to the following fuses: "C" and "9.

I had about 700 mA on fuse 9, reduced to about 75 mA once I'd found a very hot vacuum device next to the convenience module under the back seat. I changed the vacuum device for a new on and the module for a used one.

This on a W124.051. Probably a similar setup.

RayH

 

[gerryvz]

You're talking about the vacuum pump, which powers the door locks? Or a vacuum switch?

 

[gsxr]

Next to the convenience module would be the rear headrest solenoid, although on a coupé I'm not sure if there's something else in that area.

 

[rayhennig]

on a coupé I'm not sure if there's something else in that area.

You've reminded me. I'm pretty sure it is the solenoid for the front seat backs.

R

 

[M104-AMG]

<SNIP>
I'd unplug your door light switches just to rule them out. Seen them do Dumb things.

Yep, the rear doors underside lamps were always on, that was the additional draw. Gonna check out / replace the door light switches.

neil

 

[DerFuror]

Yep, the rear doors underside lamps were always on, that was the additional draw. Gonna check out / replace the door light switches.

neil

I'll be crestfallen to hear if the draw is from gray light switches

 

[emerydc8]

I'll be crestfallen to hear if the draw is from gray light switches

We do pay a price to have these irresistible chick magnets on our cars.