First my 2002 C240 showed a "Lamp Sensor - Visit Workshop" fault, although I had no problem with headlights, and it starts & drives fine. Did find the wipers didn't work in rain sensing mode. I figured I needed to replace the lamp sensor.

Then a few days later, before I could look into the sensor issue, the transmission went into safe mode and had to drive home slowly in low gear. OBD2 pulled a P0702 fault - Transmission Control Sys Electrical. Starting was still fine and there was no low voltage warning. Load test on old battery showed low charge, but was inconclusive. Alternator tested fine during load test. Decided to replace original battery.

A new battery solved all problems - lamp sensor fault immediately cleared and transmission is back to normal. If I had acted on sensor and transmission faults, could have spent much more $$$. Wonder what the $tealer would have charged?

PS - during battery swap maintained voltage using charger and avoided all errors and resets normally encountered when battery is disconnected.

 

good thinking. i am going to do it this way also.

 

The dealer would jack up your trousers and rotate your wallet. Even if it was just a battery you would have paid so much more than calling Roadside. They replace the battery for free, and charge only for the battery. They don't charge an inflated price for parts, as is the practice at many dealers.

 

I did notice that I keep getting various malfunction codes just before my battery dies. A couple of weeks ago I had ABS fault and license plate bulb fault display came on. I didn't do anything since the display disappears after you turn off and restart the car again. My battery died afterwards after leaving it in the garage for too long. After recharging the battery the fault codes stopped appearing.

 

I'm still on original battery...been getting it checked every few months...
maybe check it again today. 6.5 years on a battery. Wow.

 

When my problems started, I had Autozone check my battery (out of the car). I only checked it because another poster mentioned that his "lamp fault" was caused by a battery with a bad cell.

That's the point of my original post - I had absolutely no starting problems and no low voltage indications, just other problems that did not point directly to a bad battery.

Autozone said it showed a low charge and didn't recommend replacement, telling me that there could be another reason for the low charge. I decided to replace the 6 year old battery before looking for another cause of the lamp sensor and transmission faults, and the new battery solved both problems. I didn't have much to lose, since even if the battery wasn't the problem I knew it couldn't last too much longer.

 

Last time I had it checked they showed 600 CCA
thats less than the rated amount and down from the previous 650...
so likely I'm getting close to the time.

Maybe I should just bite the bullet..
but then, I also want to send the alt and SC out for rebuild...
for long term reliability, rather than dealing with breakdowns.
How much was the battery?
What kind did you get?

I'm quite impressed with the quality of the stock battery.

 

6.1 YEARS FOR ME!!!

 

Autozone Duralast 49-DL at $85. Specs 850 CCA and 1000 CA. I considered another MB battery, but MB roadservice might not have agreed that my battery was bad AND I wanted the car fixed quickly.

After I removed the battery hold-down bracket, I clipped my battery charger positive to the aux post and gounded it to the strut mount, and then removed the battery. About an hour later I was home after having my battery tested and buying the new one. Installed new battery, then removed charger. Absolutely no memory lost and no resets were required, and the transmission and lamp sensor issues were gone. Delay wipers are now working again.

Next day had Autozone load test alternator just to confirm there were no other problems.

 

I replaced my last ~Nov. When it was at the dealer it sat for a few days and they couldn't start it... or so they said... *rubs chin*

 

Look at the SLK forum, many people with 1998/1998 SLK230 with the original battery and the SLK probably has higher power demands on the battery because of the folding hard top.

 

is SLK230 same engine as the 2002 C coupe M111??

 

Just had the battery replaced through the dealer for $135 - Free install. This fixed the Light Sensor issue and occasional SRS not available.

Most importantly it corrected an issue that I had been having recently with the transmission. Seems that it used to get stuck while in D on the first gear (safe mode?). After a while, I would have to stop, remove the key, and restart. The car would drive normal.

 

Hi Guys,
I my car starting giving the lamp sensor warning a month or so ago but the sensor still worked so I thought nothing of it and ignored it. Then yesterday the car refused to switch out of (first?) gear and the engine light came on. I checked the engine code and it turns out it was code P0702. After reading the forums I decided to buy a new battery (Exide Performance Series 850 CCA/1000CA Type 49) as mine was original (7 years old) and on it's last legs.

After installing the new battery I no longer get the lamp sensor warnings, however the transmission issue still persists and the engine light/code came back as well.

Any ideas? Should I try charging the new battery and try again? No I need something other than a standard CANBUS code reader to get the car out of "Limp" mode? Could the alternator be dead? I'm only at 68k miles/110,000kms so I wouldn't think the alternator would be toast so soon.

Thanks in Advance,

Rich....

 

Could be the voltage regulator that sits on the rear of the alternator..

 

Hi Rich,

Back when I changed my battery, the car then returned to normal. Trans returned to normal operation without having to doing anything special. I had borrowed a fault reader from a friend when I pulled the P0702 code, and I can't remember if I used his reader to clear the faults. It was a standard ODB2 tool.

When you changed the battery did you hod voltage on the power buss as I did (I used my battery charger), until the new battery was installed?

Its been 7 months since I changed the battery, and I've had no problems with light sensor, wiper control, transmission or any other codes or electrical issues.

 

Hey thanks for the reply. Nope I didn't supply the car with power while I changed out the battery. Never have in the past when I've charged up the battery etc. Once the battery was installed I just went through the usual routine to re-calibrate the sunroof (close window, hold switch, open window hold switch), windows (hold switch up), ESP (turn wheel fully left-right), and cleared the error code using the CANBUS reader.

The lamp sensor error code did go away so the battery was definitely not working right. Just surprised the tranny issue is still there.

Right now my plan is to charge up the battery and try again tomorrow, failing that I'm not sure what to do barring having it towed to the dealer.

Rich...

 

Is there an easy why to test this out? What voltage should it be regulating to?

The other question is does anyone know the factory powertrain warranty for these cars (2002 c230 coupe)?

Rich...

 

This all makes a lot if sense. 6 years is enough for a battery. I'm going to change mine at six years & not wait for trouble - Thanks

 

I do recall Emrliquidlife had an error that put the car into limp mode until it was cleared. (Check engine light)
I started keeping an OBD tool in the car after I read that.

 

Yup, and that's why I got one too . Cept in this case I cleared it and it came back, and is still stuck in first gear.

Rich....

 

Its a known problem and the dealer would be honest about that. I have come across a dozen of the problem Neilpilot describe in the past year.

 

Have you come across any situations like mine where changing the battery fixed everything BUT the P0702 code? I've cleared it and I'm still stuck in the same gear (first?) and the code has come right back.

Rich...

 

my is car is c320 o1 and still have oem battery little bit over 7 year. wonder if i should replace it soon.

 

Toss it - trouble is on the horizon