C180 W202 Bizzare Battery Drain

guptalloyd

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Jul 15, 2011
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Evening all, hope this is the right discussion area for this post.

I've owned the 180 for 3 months now (98) without any problems, until Monday when I went to start and the battery was drained. RAC called, battery was at 6V, so charged. He suspected interior light so manually switched off so light doesn't come on with doors.

Forwards to yesterday evening, car running fine all week, around 150 miles driven no short journeys etc.. Tried to unlock car with keyfob but not enough power. Checked battery and it read 1.4V. Managed to get battery charged up again and gave it a run. I used a meter in in line, by taking the negative off the battery and connecting the meter between the neg lead and the battery to see what drain there was: 0.21A, with everything off. Mr.RAC had advised anything upto 0.5A a good battery should cope with, but they like to see around 0.3A tops. Bewildered I left car and went to bed.

This afternoon, opened car, key in, dash lights on bright, went to start, not enough power to turn over, battery drained in attempt to start. I got meter and it read 7V this time - also drain was 0.85A, ahaa I thought and hailed my lovely assistant (the OH). While she read meter I started popping each fuse out until drain dropped. Fuse 29 seemed to be the culprit, after removal drain would drop to around 0.19A. So I'm thinking, OK found whats draining it, I'll leave fuse out tonight, and put back in the morning.

Fuse 29 according to the yellow card in the fuse box lid, says "Blower motor (heater/AC)". But when I remove it, the heater still blows whatever air I want it to, hot or cold, and at whatever speed. Hmmm odd. So sat idling on the drive, I removed fuse 29. Oh dear, heat needle rises steadily to 120oC, but not into red, and engine fan runs flat out, I reinserted fuse to no avail. Took for a short drive to get some cool (ish) air in but sitting just under 120oC. Got back home, turned straight off, then started straight away, needle returns to the usual midway 80oC position, everything seems normal again. Odd! Definately related to Fuse 29!

Test run all OK except electric windows: when I press button fully for auto down, the window will not move, I have to half press the button and hold to wind windows up/down, not sure if this is related as I haven't noticed it before.

I'm just wondering if anyone else has experienced anything similar, and if Fuse 29 really is as it says Heater Blower? And maybe point me in the right direction before a nasty bill!

Cheers
JW
 

Harrythedog

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Don't know about the battery drain but the windows may need resetting. Close the drivers window and keep the button pressed for a couple of seconds then do each window the same
 

WG M-B

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Its very difficult to tell with battery drains and finding the problem can take quite a long time. However the alarm siren would be a good place to start on a 202. Its fitted under the inner wheel arch liner on the front. You can just disconnect it. And 0.5 amp is far too large a drain.
 
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guptalloyd

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Jul 15, 2011
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Cheers.

I tried the windows trick to no avail but they started working again today of their own accord!

Also, the car remote locks OK but used to sound one beep when opening, then three beeps when locked - this has now stopped. Also in the rain the sounder used to sound like it had water in it, and would emit a crackly sounding beep - maybe pointing to a short, so will have a look at that one alf.

But maybe I deserve dummy of the year award, I've just parked the car up, for it's overnight rest, and took fuse 29 out in preperation (like I did last night, batt was fine this morning), then looked, and realised it's actually Fuse 30, duh! I thought a 10A fuse was a bit small for a Blower Motor
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So, that minor issue ironed out, Fuse 30 is for Air Con/Automatic Heater Control/Engine Residual Heat System/Instrument Cluster. Which changes the game a bit. I'm guessing the residual heat system relates to the 'rest' button, so I've read it activates a small pump to circulate coolant to provide heat when the engines turned off, maybe that could be at fault, or is there an ECU that control the Air Con etc. that could be duff?

For the time being removing a fuse every night seems (touch wood) to work, but it's only been one night, so to early to tell, and my meter has blown a fuse now
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Not sure what to check or test now, I wonder if the alarm sounder is linked to that fuse, and it's totally packed up now, will take a look tomorrow if it stops raining!!
 
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guptalloyd

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Alf, excuse my ignorance, but will I have to remove the inner wheel arch liner to access the siren, and if so is it drivers or passengers side?

Cheers
 

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