Technical Ducato X250 Battery light on Dash

[mharris5]

Motorhome based on Ducato X250, Battery light on dash.

I have a Bessecarr E520 2008 motorhome, and have a very annoying fault that you might be able to help me with. My Cab battery was prettty flat, and I Started the motherhome anyway, it started, but the Alternator failed. New alternator fitted, but I still have a battery light on the dashboard, and my hab battery does not recieve charge from the alternator. Vehicle battery charging fine. Alternator output on D+ is solid 14.4, and the wire that comes into D+ has 8.4V with ignition on (I'm assuming a volt drop over warning light)

Where does the motorhome get the D+ signal from to activate the split charge relay? and is this on the back of the fuse panel? When plugged into mains, the hab battery charges fine, and if I select the Cab battery on the control panel, that charges fine too. It looks as though the control panel no longer can see D+, and therefore does not know if the engine is running. Could I have blown something? I have checked every fuse and relay in The Engine Bay, dash, and drivers side areas, and all are fine.

 

[Communicator]

Hi,
Welcome to the forum. As you do not offer thanks in advance, I am hoping that you will be good enough to post the eventual outcome.
Perhaps more important than your MH make/model would be the make of the MH 12V electrical system, e.g. Schaudt, Sargent, CBE etc.
You have not mentioned jump starting, which can cause problems on motorhomes. If the split charge relay becomes operated, excessive current may flow from the habitation battery (B2) into the cab battery (B1). This may blow the fuse connecting the habitation electrics to B1. This fuse should be located as close as practicable to B1. The underfloor battery box would be a good place to look. A more serious possibility is that the MH 12V distribution board could be damaged before the fuse blows.

You have not stated whether the engine was running, when you measured the D+ voltage. I would expect to read approximately 14V on the D+ node if the engine was running. Also according to the attached drawing the D+ is connected to M001 which is the Body Computer Module (BCM). The warning light is controlled by the BCM.

Where the D+ signal is taken from is conveter specific. If your vehicle has a Fiat supplied converters panel at the base of the RH "B" pillar, then I would expect it to be taken from there, as an active low signal. (Connects to 0V or earth when alternator is generating.) This requires a converter supplied relay to convert to active high (+12V). Hymer supply a relay box that provided multiple outputs for both D+ and IGN+. Relay failures are rare, but they can occur.

If your vehicle does not have the converters panel, then the D+ connection will probably be connected close to the BCM. See again the attached diagram, which I have saved from a previous thread. Lower RH corner M001 is the BCM. D+ is the bottom wire in the diagram connector A pin 25 colour is shown as MV, which equates to brown/green. Look for an extra wire connected there.

 

[mharris5]

Hi,
Welcome to the forum. As you do not offer thanks in advance, I am hoping that you will be good enough to post the eventual outcome.
Perhaps more important than your MH make/model would be the make of the MH 12V electrical system, e.g. Schaudt, Sargent, CBE etc.
You have not mentioned jump starting, which can cause problems on motorhomes. If the split charge relay becomes operated, excessive current may flow from the habitation battery (B2) into the cab battery (B1). This may blow the fuse connecting the habitation electrics to B1. This fuse should be located as close as practicable to B1. The underfloor battery box would be a good place to look. A more serious possibility is that the MH 12V distribution board could be damaged before the fuse blows.

You have not stated whether the engine was running, when you measured the D+ voltage. I would expect to read approximately 14V on the D+ node if the engine was running. Also according to the attached drawing the D+ is connected to M001 which is the Body Computer Module (BCM). The warning light is controlled by the BCM.

Where the D+ signal is taken from is conveter specific. If your vehicle has a Fiat supplied converters panel at the base of the RH "B" pillar, then I would expect it to be taken from there, as an active low signal. (Connects to 0V or earth when alternator is generating.) This requires a converter supplied relay to convert to active high (+12V). Hymer supply a relay box that provided multiple outputs for both D+ and IGN+. Relay failures are rare, but they can occur.

If your vehicle does not have the converters panel, then the D+ connection will probably be connected close to the BCM. See again the attached diagram, which I have saved from a previous thread. Lower RH corner M001 is the BCM. D+ is the bottom wire in the diagram connector A pin 25 colour is shown as MV, which equates to brown/green. Look for an extra wire connected there.

Hi,
Absolutely awesome reply here with some great information. I'll check that pin 25 for continuity and see if I can spot any links on there. I have also recieved some great information from ApulJack electronics, who tell me that D+ signal should be recieved on Pin 2 of JP14, the green 4-way connector on the fuseboard (NE184) So Hopefully with all this new information I will be able to trace the fault backwards from the Fuseboard.

I will update the post with my findings once I get chance to look at it again this week.

 

[mharris5]

for information, motorhome is Bessecarr E520, 2008, based on X250 ducato. Hab control panel is NE183-M8, and Fusboard/relay unit is NE184.

 

[mharris5]

Update.

Tested the d+ onput on pin 25 of the body control module. Puts out 9.69v with ignition on. This is supplied from here to d+ on the alternator to excite the windings. Plugged connector back on the alternator and started the engine. Measured 14.2v at pin25 on body control module, so you would think the bat warning light would go off, as this is exactly the signal expected. Could it be a fault on the dash as the alternator seems to be working perfectly. Voltage on cab battery with engine running, 14.6v.

Disconnected connector from bcm and alternator, and tested for any earth, and its clear as a bell. I'm totally stumped now.

 

[rayc]

Update.

Tested the d+ onput on pin 25 of the body control module. Puts out 9.69v with ignition on. This is supplied from here to d+ on the alternator to excite the windings. Plugged connector back on the alternator and started the engine. Measured 14.2v at pin25 on body control module, so you would think the bat warning light would go off, as this is exactly the signal expected. Could it be a fault on the dash as the alternator seems to be working perfectly. Voltage on cab battery with engine running, 14.6v.

Disconnected connector from bcm and alternator, and tested for any earth, and its clear as a bell. I'm totally stumped now.

If the lamp is on with D+ disconnected at the alternator then something else is causing the lamp to stay on. I presume the 9.69v is the reading with the lamp in circuit. Is the lamp lit at that point as the volts drop would appear to be across the bulb?

 

[mharris5]

If the lamp is on with D+ disconnected at the alternator then something else is causing the lamp to stay on. I presume the 9.69v is the reading with the lamp in circuit. Is the lamp lit at that point as the volts drop would appear to be across the bulb?

I assume lamp would come on with the d+ disconnected as the bcm would not see an earth. The light is controlled by the computer. I'm thinking now they have given me the wrong typ of alternator, perhaps there are subtle differences in the rectifier diodes, and hence voltages.

 

[rayc]

I assume lamp would come on with the d+ disconnected as the bcm would not see an earth. The light is controlled by the computer. I'm thinking now they have given me the wrong typ of alternator, perhaps there are subtle differences in the rectifier diodes, and hence voltages.

My understanding is that with ignition ON engine not running: The lamp will be ON as terminal B+ gets a ground via the alternator.
Disconnect B+ at the alternator the lamp should go out as no path to ground.
With B+ reconnected and engine started B+ should rise to alternator voltage and the lamp should go out.

I may off course be wrong and not quite grasp the concept so will eagerly await your outcome which i am sure will be successful.

 

[Communicator]

mharris5,

I was initially privately sceptical regarding the unsuitability of the replacement, but the information presented here and elsewhere has made me rethink. Non compatability does fit the facts, particularly if your MH has a converters panel, or directly uses the active low output from the BCM to operate the split charge relay.