fast28
Senior Member
- Joined
- Nov 8, 2010
- Messages
- 146
- Reaction score
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- Location
- Glos
- Your Mercedes
- SL55-conversion (R129) & CL63 AMG (W216)
Some weeks ago I had the mishap of one of every car owner's worst nightmares - attaching a reverse charged battery in a car stacked with sensitive electronics. During August I went on holiday and asked my Father to give the car a run or two to ensure the battery did not go flat, it has a habit of going flat after about 10 days; it's an original MB battery so 13 years old. On my last day away I got a rather anxious call to tell me the alarm was going off and "how does one turn it off?" I instantly knew the battery had lost charge and almost inevitably the result was the alarm sounding. It was slightly unusual in the fact the car had been run twice with no reported problems so it appeared the battery was now hardly able to hold charge being left for more than 5 days or so or an electrical item had not switched off. My Father was unable to open the boot with the mechanical key as it requires a certain "knack" so the alarm continued until there was no charge remaining to power it..
Arriving home to a quiet "dead" car I disconnected the battery terminals and measured the voltage, it was just over 8V. I placed my smart charger on the battery and left it for 16 hours. The next day I connected up the freshly charged battery, noting a few sparks than normal when the negative terminal was connected. I walked to the open driver's door and immediately noticed wisps of smoke and a strong burning smell coming out of the central front vents and also the windscreen wipers were on even though they were switched off!. I quickly disconnected the battery and tried to understand what had happened.
Checking the fuses for the faulty circuit I found that more than one fuse had blown; Comand and navigation system, ignition coils, linguatronic ABC and windshield washer system, all three fuse boxes had blown fuses!
Obviously something serious had happened, the battery appeared to have lost all its charge as nothing was working. Taking the battery out of the car and placing on a bench I hooked the charger up again, immediately the fuse on the charger blew, replaced fuse, it blew again, mmm tok a voltage reading with a multimeter: -3V placed the meter leads on the opposite terminals, positive on negative terminal: 3V! The battery had reverse polarity, how, I do not know, the times I've charged car batteries; I've never reverse-charged a battery and besides my smart charger surely would have blown its fuse?? I ordered a new battery online and thought I would discharge the existing battery by connecting a headlight bulb across the terminals and try to charge it again. After discharging the battery as much as possible still showing a small negative voltage I attached the battery charger again, it didn't blow the fuse so I left it to charge. The next day I found the charger had blown it's fuse again so gave up on it.
With a fresh new battery connected up to the car I anxiously observed the interior for signs of smoke - none, and the reassuring sound of the soft-close windows operating could be heard. But not all was right, the drivers door electronics would not work with the ignition in position 2 and the window would not go up although the soft-close feature was working, it was working for the passenger side. The courtesy side and fog light feature only worked on one side and the ABS, ESP, BAS and distronic systems were offline even after synchronising the steering angle sensor. The car started and ran fine although the engine was a little uneven at idle and the interior lights pulsed with the engine. I ran the car to work and back a distance of 45 miles and also noticed the Comand would not wake-up on the CAN and had to be manually turned on and off, it also gave a battery warning so I switched it off and noted the problem as another issue to look into. The next day I took the car into work, it was a dark rainy morning and my lights had come on, after 5 miles or so I was met by a red battery warning and within 2 minutes everything started to shut down one by one, dash lights, exterior lights, engine power, PML steering assist, making it to a car park under very low power I knew all hope was lost of making it to work and the battery was obviously not charging! The next couple of hours involved the RAC, a loan of a get-me-home battery and the news that my alternator was probably kaput .
With some web research I concluded that my alternator's voltage regulator or most likely rectifier had blown and a likely replacement was needed. On further deep research of the problem I found out that there were two more fuse locations - one under the driver's footwell and one in the boot behind the battery mounted above the wheel arch. WIS confirmed the locations and I began the arduous task of removing the footwell carpet which involved removing the sill trim, accelerator pedal, side panel and lower dash panel. Upon discovering the fusebox known as X4/10 and removing the cables that fed power from the alternator to the battery and elsewhere I opened up the unit...
Testing the continuity of the fuses I found the "smoking gun", the "midi" 150 amp fuse was blown on the alternator to battery circuit. After ordering the fuse online from an Ebay seller and eventually fitting it I measured the voltage at the battery - 14.2V . Now the alternator was charging the battery and one problem was solved. As one problem went another was discovered, I had no a/c blower speed apart from full-on. Another day was spent taking the passenger side lower dash cover off to access the blower fan regulator. Sure enough the speed regulator had burnt out, this must have been the cause of the smoke coming out through the central vents! A new regulator was ordered and blower speed restored although now I have a one constant low speed at all settings
More of an issue was the ABS fault light which seemed to have switched off the BAS, ESP and distronic (although it said "speedtronic"). This certainly wasn't going to be the usual brake switch fault; all brake lights were working. The steering alignment was good so I investigated the wheel speed/ABS sensors, the navigation system was picking up a speed signal and my dash was displaying the car's speed correctly. Interestingly disconnecting a front ABS sensor caused a white ABC warning to come on and the PML steering electric assist to switch off. Using a newly bought Launch Creader VII+ diagnostics reader which can read the four main systems - engine, ABS, Airbags and transmission I was able to read a recurring single fault code - C1011 - A7/3 Traction system hydraulic unit - open or short. After interrogating the ABS pump wiring and relay I found the pump was getting voltage so the only other voltage supply had to come from the ESP-PML-BAS control unit to the A7/3 ABS valves. Internet research revealed a few companies offering to rebuild Mercedes ESP modules and one known cause was C1011. A search of Ebay found a seller offering a used ESP-PML-BAS control unit from an S-class W220 but it had the same MB and Bosch part numbers as my existing unit. So tonight I fitted the unit and bingo! ABS light goes out and the associated ESP, BAS and speedtronic warnings . No fault codes stored.
So now I have a healthy car back on the road. The cost of this electrical disaster? ...
New battery - £80.
New midi fuse - £1.50
Bunch of blade fuses - £3
New blower regulator - £28
Used ESP-PML-BAS ECU - £70
Was I lucky or unlucky in terms of the damage I don't know? but what I can't understand is how the polarity reversed on the battery, did I charge the battery the wrong way around, if so why didn't the fuse blow on the charger or did the battery have a failure???
Still have to sort out the blower speed problem though...
Arriving home to a quiet "dead" car I disconnected the battery terminals and measured the voltage, it was just over 8V. I placed my smart charger on the battery and left it for 16 hours. The next day I connected up the freshly charged battery, noting a few sparks than normal when the negative terminal was connected. I walked to the open driver's door and immediately noticed wisps of smoke and a strong burning smell coming out of the central front vents and also the windscreen wipers were on even though they were switched off!. I quickly disconnected the battery and tried to understand what had happened.
Checking the fuses for the faulty circuit I found that more than one fuse had blown; Comand and navigation system, ignition coils, linguatronic ABC and windshield washer system, all three fuse boxes had blown fuses!
Obviously something serious had happened, the battery appeared to have lost all its charge as nothing was working. Taking the battery out of the car and placing on a bench I hooked the charger up again, immediately the fuse on the charger blew, replaced fuse, it blew again, mmm tok a voltage reading with a multimeter: -3V placed the meter leads on the opposite terminals, positive on negative terminal: 3V! The battery had reverse polarity, how, I do not know, the times I've charged car batteries; I've never reverse-charged a battery and besides my smart charger surely would have blown its fuse?? I ordered a new battery online and thought I would discharge the existing battery by connecting a headlight bulb across the terminals and try to charge it again. After discharging the battery as much as possible still showing a small negative voltage I attached the battery charger again, it didn't blow the fuse so I left it to charge. The next day I found the charger had blown it's fuse again so gave up on it.
With a fresh new battery connected up to the car I anxiously observed the interior for signs of smoke - none, and the reassuring sound of the soft-close windows operating could be heard. But not all was right, the drivers door electronics would not work with the ignition in position 2 and the window would not go up although the soft-close feature was working, it was working for the passenger side. The courtesy side and fog light feature only worked on one side and the ABS, ESP, BAS and distronic systems were offline even after synchronising the steering angle sensor. The car started and ran fine although the engine was a little uneven at idle and the interior lights pulsed with the engine. I ran the car to work and back a distance of 45 miles and also noticed the Comand would not wake-up on the CAN and had to be manually turned on and off, it also gave a battery warning so I switched it off and noted the problem as another issue to look into. The next day I took the car into work, it was a dark rainy morning and my lights had come on, after 5 miles or so I was met by a red battery warning and within 2 minutes everything started to shut down one by one, dash lights, exterior lights, engine power, PML steering assist, making it to a car park under very low power I knew all hope was lost of making it to work and the battery was obviously not charging! The next couple of hours involved the RAC, a loan of a get-me-home battery and the news that my alternator was probably kaput .
With some web research I concluded that my alternator's voltage regulator or most likely rectifier had blown and a likely replacement was needed. On further deep research of the problem I found out that there were two more fuse locations - one under the driver's footwell and one in the boot behind the battery mounted above the wheel arch. WIS confirmed the locations and I began the arduous task of removing the footwell carpet which involved removing the sill trim, accelerator pedal, side panel and lower dash panel. Upon discovering the fusebox known as X4/10 and removing the cables that fed power from the alternator to the battery and elsewhere I opened up the unit...
Testing the continuity of the fuses I found the "smoking gun", the "midi" 150 amp fuse was blown on the alternator to battery circuit. After ordering the fuse online from an Ebay seller and eventually fitting it I measured the voltage at the battery - 14.2V . Now the alternator was charging the battery and one problem was solved. As one problem went another was discovered, I had no a/c blower speed apart from full-on. Another day was spent taking the passenger side lower dash cover off to access the blower fan regulator. Sure enough the speed regulator had burnt out, this must have been the cause of the smoke coming out through the central vents! A new regulator was ordered and blower speed restored although now I have a one constant low speed at all settings
More of an issue was the ABS fault light which seemed to have switched off the BAS, ESP and distronic (although it said "speedtronic"). This certainly wasn't going to be the usual brake switch fault; all brake lights were working. The steering alignment was good so I investigated the wheel speed/ABS sensors, the navigation system was picking up a speed signal and my dash was displaying the car's speed correctly. Interestingly disconnecting a front ABS sensor caused a white ABC warning to come on and the PML steering electric assist to switch off. Using a newly bought Launch Creader VII+ diagnostics reader which can read the four main systems - engine, ABS, Airbags and transmission I was able to read a recurring single fault code - C1011 - A7/3 Traction system hydraulic unit - open or short. After interrogating the ABS pump wiring and relay I found the pump was getting voltage so the only other voltage supply had to come from the ESP-PML-BAS control unit to the A7/3 ABS valves. Internet research revealed a few companies offering to rebuild Mercedes ESP modules and one known cause was C1011. A search of Ebay found a seller offering a used ESP-PML-BAS control unit from an S-class W220 but it had the same MB and Bosch part numbers as my existing unit. So tonight I fitted the unit and bingo! ABS light goes out and the associated ESP, BAS and speedtronic warnings . No fault codes stored.
So now I have a healthy car back on the road. The cost of this electrical disaster? ...
New battery - £80.
New midi fuse - £1.50
Bunch of blade fuses - £3
New blower regulator - £28
Used ESP-PML-BAS ECU - £70
Was I lucky or unlucky in terms of the damage I don't know? but what I can't understand is how the polarity reversed on the battery, did I charge the battery the wrong way around, if so why didn't the fuse blow on the charger or did the battery have a failure???
Still have to sort out the blower speed problem though...