SL 350 battery light on dash - can anyone help??

[Michael F]

I wonder if the way the problem manifests gives a hint of the root cause:

Car operates well from ignition start. After approx 30min/40min the red battery fault at the IP turns on. Stays on until I reset with the iCarsoft i980.
One way to avoid the red-light coming on is to stop the car before running 30min, turn ignition off, then start again. Somehow this resets to zero the fault display logic, hence can run another 30/40 min without the red light coming on. (still the reality is that the front battery is not being recharged by the car alternator)

 

[mioba]

The car is simply running and in the background it will kick up a pending fault, which it will then register as a fault by showing the message on the screen, clearing the fault and switching off and on every 30 mins wont recitify the fault.

The computers in the car are contantly looking for faults.

Have you checked the volatage of both batteries with ignition off, and then with ignition on - as mentioned.

One battery is clearly getting charged so the alty is fine, what controls voltage getting to the other battey is the fault.

If you google the pn it will give an idea of price, but the pn may have been superceded. Consider looking on MBGT website or MB reman.

good luck and keep us posted.

 

[LostKiwi]

Sounds like the BCM is faulty.

Part number looks to be 2305401045

Be sure to be seated when looking at prices....

 

[Michael F]

Thanks mioba+LostKiwi. A salvage module is between £400 / £500. It is not the kind of money I fancy spending unless I am certain it’ll get the issue fixed. In my experience, semiconductors don’t fail - failures I have seen on modules are generally due to internal pcb mounted fuses, corroded connectors, or capacitors. Unless someone gives me some extra light on this problem, I will be removing the BCM from the car, open it for inspection of internal componentes, check relays, and clean up connectors. Will also try to check the sensors that govern the dc/dc logic. If after fitting all back the problem still remains, I will most probably take a dive and buy a salvage controller.
Will do my best to report back here - timing for all this tbd.

 

[LostKiwi]

Annoyingly you can replicate the primary function of the BCM very easily using a voltage sensitive relay and they cost buttons. Even a high end split charge controller such as often used in marine applications only cost 1/2 the cost of a used BCM.
There's a part of me tempted to try a VSR if my BCM ever gives up.

0.0V Drop Alternator Splitter Pro Split R

Instruction Manual PDF Product Information PDF DC Voltage Max Alt Amps Battery Banks Size L x W x D mm Weight Kg Part Number 12 120 2 150 x 80 x 120 0.6 PSR122 12 180 2 150 x 80 x 140 0.7 PSR182 12 250 2 150 x 80 x 155 0.9 PSR252 12 120 3 150 x 80 x 130 0.9 PSR123 12 180 3 150 X 80 X 150 1.0...

sterling-power.com

 

[mattkh]

Agree. Still appreciate mattkh's input.

Thanks.
Without a circuit diagram of the logic behind charging two batteries in parallel, what was going through my mind was the effect of different internal resistances of the two batteries.
If the one in the front has a higher internal resistance (as result of age), then the rear battery will get more charging current.

 

[mioba]

A simple test of the voltage across the front battery when running will tell if its getting any charge at all

 

[mioba]

Annoyingly you can replicate the primary function of the BCM very easily using a voltage sensitive relay and they cost buttons. Even a high end split charge controller such as often used in marine applications only cost 1/2 the cost of a used BCM.
There's a part of me tempted to try a VSR if my BCM ever gives up.

0.0V Drop Alternator Splitter Pro Split R

Instruction Manual PDF Product Information PDF DC Voltage Max Alt Amps Battery Banks Size L x W x D mm Weight Kg Part Number 12 120 2 150 x 80 x 120 0.6 PSR122 12 180 2 150 x 80 x 140 0.7 PSR182 12 250 2 150 x 80 x 155 0.9 PSR252 12 120 3 150 x 80 x 130 0.9 PSR123 12 180 3 150 X 80 X 150 1.0...

sterling-power.com

no bodge jobs/cutting corners LK, its not your style......

 

[peterws1957]

Thanks mioba+LostKiwi. A salvage module is between £400 / £500. It is not the kind of money I fancy spending unless I am certain it’ll get the issue fixed. In my experience, semiconductors don’t fail - failures I have seen on modules are generally due to internal pcb mounted fuses, corroded connectors, or capacitors. Unless someone gives me some extra light on this problem, I will be removing the BCM from the car, open it for inspection of internal componentes, check relays, and clean up connectors. Will also try to check the sensors that govern the dc/dc logic. If after fitting all back the problem still remains, I will most probably take a dive and buy a salvage controller.
Will do my best to report back here - timing for all this tbd.

I would be spending £60 ish on a Star diagnosis at a reputable indie before spending any more time and certainly any cash on the issue.

 

[Michael F]

Thanks for all your comments.
matIh,míoba the front battery is new - it never gets any charging current.
LostKiwi, I would fear embarking in your “voltage sensitive relay”. I think I would probably cause lots of collateral damage when having to splice and rework the wiring harnesses, plus I don’t have a proper workshop.
Peterws. The experience I have with indies hasn’t been great. Do you know anyone strong in electrics? (as near as possible to Wandsworth)
I will start revising connectors for corrosion and possibly will take apart the BCM for inspection.

 

[mioba]

Not wanting to offend, but you dont seem most technically minded, but as said not wanting to offend.

If you do take the BCM apart then be ready to shell out for a new one.

Aside have you had the codes read on the car.

I cant imagine an auto spark telling you whats in this thread.

All that aside, keep us updated and good luck.

 

[Michael F]

Not wanting to offend, but you dont seem most technically minded, but as said not wanting to offend.

If you do take the BCM apart then be ready to shell out for a new one.

Aside have you had the codes read on the car.

I cant imagine an auto spark telling you whats in this thread.

All that aside, keep us updated and good luck.

The reason to inspect the BCM (open the metal cover) is to check for the possibility that there is a blown pcb mounted fuse. I have in the past come across electronic controllers that stopped working because of blown pcb mounted fuses. Of course, it is quite possible I take the cover and find there is no pcb fuse - I’d wished I had the Bosch circuit diagram to find out in advance. Once verified and OK, the metal cover will be screwed back and BCM mounted back in the car - all in all it is not a massive piece of work - don’t see the logic behind being “ready to shell the BCM out for a new one” (?).
All that aside, do you know of a good autospark near Wandsworth that could help?

 

[-raj-]

shame you are not closer to me, i fix quite of few of these red battery warning issues.

Its either:
F52f1
F52f2
F32
F33
K57 Relay
K75 Relay
or finally N82/1 module

You need to have star diagnostics with you to go through each component to test.

I have changed a few BCM units with no visible damage inside

My advice would be to get it on star for a scan first.

 

[peterws1957]

Thanks for all your comments.
matIh,míoba the front battery is new - it never gets any charging current.
LostKiwi, I would fear embarking in your “voltage sensitive relay”. I think I would probably cause lots of collateral damage when having to splice and rework the wiring harnesses, plus I don’t have a proper workshop.
Peterws. The experience I have with indies hasn’t been great. Do you know anyone strong in electrics? (as near as possible to Wandsworth)
I will start revising connectors for corrosion and possibly will take apart the BCM for inspection.

Sorry I live in the grim north. Down south is an unknown territory. Could someone on here suggest a reputable indie for the OP?

 

[mioba]

The reason to inspect the BCM (open the metal cover) is to check for the possibility that there is a blown pcb mounted fuse. I have in the past come across electronic controllers that stopped working because of blown pcb mounted fuses. Of course, it is quite possible I take the cover and find there is no pcb fuse - I’d wished I had the Bosch circuit diagram to find out in advance. Once verified and OK, the metal cover will be screwed back and BCM mounted back in the car - all in all it is not a massive piece of work - don’t see the logic behind being “ready to shell the BCM out for a new one” (?).
All that aside, do you know of a good autospark near Wandsworth that could help?

ok then, taking a cover off is the not the same as taking apart.

Keep us posted and good luck.

 

[mattkh]

The reason to inspect the BCM (open the metal cover) is to check for the possibility that there is a blown pcb mounted fuse.

Pressing a reset button works OK with electronics.
How about just unplugging the BCM, waiting a few minutes for it to reset, then putting the plug back in.

 

[Michael F]

shame you are not closer to me, i fix quite of few of these red battery warning issues.

Its either:
F52f1
F52f2
F32
F33
K57 Relay
K75 Relay
or finally N82/1 module

You need to have star diagnostics with you to go through each component to test.

I have changed a few BCM units with no visible damage inside

My advice would be to get it on star for a scan first.

Hi raj,
wonderful comments.
I already did the F52s both the 100 and 200 amp. Tedious access. Was convinced it was that - my surprised when I verified that both fuses were OK (took them out and measured with an Ohm meter)
I will check 32, 33, and will try to inspectK57 and K75.
I have the premonition that the BCM N82/1 is OK because the car seems to operate well on emergency start mode (i.e. when the auxiliary battery is below 10.5 V after parked 2 weeks untouched).
How far are you from London?

 

[Michael F]

Pressing a reset button works OK with electronics.
How about just unplugging the BCM, waiting a few minutes for it to reset, then putting the plug back in.

I have done recently the equivalent of this when replacing the boot auxiliaries battery. I don’t think the starter battery feeds the BCM under ignition key off conditions. Thanks anyways.

 

[-raj-]

Hi raj,
wonderful comments.
I already did the F52s both the 100 and 200 amp. Tedious access. Was convinced it was that - my surprised when I verified that both fuses were OK (took them out and measured with an Ohm meter)
I will check 32, 33, and will try to inspectK57 and K75.
I have the premonition that the BCM N82/1 is OK because the car seems to operate well on emergency start mode (i.e. when the auxiliary battery is below 10.5 V after parked 2 weeks untouched).
How far are you from London?

Hi Michael, Im in Coventry myself

 

[teaspoonasaurous]

I am similarly confused by a red battery light. It could be the bcm, but I'll check the fuses first.