Technical Engine sense wire for 12V to habitation

[dsl101]

Got a 2009 1.9TD based motorhome (McLouis), and on checking recently after winter, it has all sorts of electrical issues. The leisure battery was dead due I think to a short somewhere in the habitation side. Both that and the engine battery were on a solar charger, and the engine battery is fine, and it started first time.

However, we have no 12V from the alternator to the habitation now when the engine is running. I've found the relay near the engine battery, and it has 2 small wires which get 12V across them when the engine is running, and 2 large wires which give 14V once running—I guess these come straight from the alternator.

I removed the relay and tested it on a bench power supply, and it's closing fine at 12V, taking about 120mA which seems about right for that sized relay. But on reconnecting it to the leads, it doesn't close when the engine is running, even though it has 12V across the coil. The current that signal wire supplied was nowhere near 120mA, and not enough to activate it. But the wire (2.5mm grey) just disappears into the bundle, and I've no luck tracing it.

Does anyone know where that will go? Will it be into the fusebox area in the cab? Or directly to the alternator in the engine compartment? Or somewhere else?

I'm hoping it's just some corrosion on the connectors that causing it to fail...

Many thanks,

David

 

[Communicator]

I am struggling to understand what your base vehicle is. You do not mention Fiat, Citroen, or Peugeot. According to Wikipedia, a 1.9TD was not offered after 2001. Perhaps if your base vehicle is one of the above makes, you could quote the first three numbers of the VIN?

The figures that you quote for the split charge relay are in the right range. Are you measuring the voltage across the relay coil connections with the relay removed? Much easier to do but you could be reading 12V through a high resistance. I keep repeating that modern multimeters can be deceptive due to their high sensitivity.

The voltrage on a D+ connection should be higher than 12V with the engine running, upto 14.4V.

The initial source for operating the split charge relay is the alternator field terminal D+, but in recent vehicles the BCM computer is in the loop. Some converters connect two relay coils in parallel to D+, these are a fridge (12V) relay, and a split charge relay. In order to avoid overloading the sensitive D+ point, it is good practice to connect only the fridge relay to D+, and then energise the split charge relay from the fridge relay output. (Assuming 3 way and not compressor fridge.)

Also please note that the split charging circuit should have fuses as close as practicable to both starter, and habitation batteries. Rating will be in the range 20A to 50A.

Corrosion on the terminals of relays located under the bonnet, has been reported as a cause of problems.

If your MH has CBE electrics then D+ is not used. The system generates its own simulated D+, but in this case I would not expect habitation related relays to be under the bonnet.

Hope that the above helps. Please report your resolution on this thread.

 

[dsl101]

Thanks for the quick reply—apologies, typo on the year, it's a 2000 (W reg) Fiat Ducato base. VIN starts ZFA.

The relay coil measures about 90Ω, and on my bench power supply at 12V draws 130mA, which all seems right, so I don't _think_ the relay is the issue. The relay coil terminals in the engine bay measure 12V without the relay in place, and 2.8V with, which I guess explains why the relay won't close. The other, larger cables read 14.2V when the engine is running.

There's a 30A fuse (removed) right by where the leisure battery normally is, and I've also disconnected as many of the other habitation-side connectors as I can find, including a fuse panel with what I'm guessing is the fridge supply, so I'm hoping the fridge is not in circuit at the moment, but not 100% certain. It is a 3-way fridge, yes. I traced the larger relay connector to this panel, so I'm fairly sure this is where the engine-based power comes in to the habitation.

So, does all that suggest the relay coil is energised straight from the alternator? Or given the voltage difference (12V vs 14.2V), does that mean it's coming from somewhere else?

Many thanks,

David

 

[Communicator]

Hi David,
It's the first three numbers, in the VIN that matter. So given the correct year, yours should read ZFA230nnnnnn,,,,,,, In other words an x230.

The only source of wiring info for the x230 base vehicle of which I am aware, is a German language workshop manual, which is available in the downloads section of this forum. I have previously extracted the wiring diagrams from that source, and added a colour code translation table. There is an English translation of the manual, but it does not seem to include the wiring diagrams. Also it should not affect you, but no engine wiring diagrams for the common rail diesels. I will attach the Starting and Recharging diagram which is relevant to you problem. The diagram is divided into a schematic on the left, with matching wiring details on the right.

If you look at the lower left centre the alternator rotor (field) is designated with a "G", and the D+ is the wire labelled 1070. This can be matched on the RHS with the alternator designated "1020". The D+ arrives on the instrument panel at pin 4 of a connector. Looking at the instrument panel icon (0004) on threRHS, pin 4 of the matching connector has a wire coded NR/VI. Translates to Black/Violet.

If you re-read my previous post, it is possible for the split charge relay coil to be supplied via the fridge relay. If fridge supply disconnected???????

Have you checked for wiring details in the McLouis handbook, as most of the wiring that you are investigating seems to be installed by the converter.

Alan

 

[dsl101]

Wow, thank you for extracting all that. It will take me a few days to get back into the van and have a proper look with your information, so i just wanted to say thanks. I'll update when I find anything more.

 

[dsl101]

Well, I finally got into the van this weekend, and didn't have any joy tracing the engine running wire from the relay (and there's nothing helpful in the scant McLouis 'handbook', which is a generous term for the photocopied sheets we have .

I did find that both the relay under the bonnet and the connector at the fuse board in the habitation area had 12V on them even when both unplugged, so they do obviously split from somewhere else. There is a 20A fuse in that board with what could be a symbol for the fridge, but I'm not 100% certain. I disconnected as much as possible anyway.

Taking the dashboard cover off, I was able to get to another bunch of relays below the main van fuse board. I reseated those as best I could, as well as all the spade connectors on the back of the fuse board itself, and lo and behold, the charging relay is now working again, closing quite happily when the engine is running, and sending 14.4V to charge the leisure battery. So I'm guessing it was simply a high-resistance connector through corrosion somewhere that is now good again.

I did look at this manual: https://www.fiatforum.com/downloads/ducato-93-x230-workshop-manual.465/ although I don't think it has wiring diagrams, and my Italian is non-existent. The German & translated ones you referenced, although covering the right years, don't actually list the 1.9TD engine at the start, so I'm wondering if they are for this specific model.

In any case, the engine side is working again now, so thanks again for the info. All that's left is to work out what originally shorted and caused the issues. The habitation fuse board has some corrosion on it, so I suspect it's to blame. It looks like it's had water on it at some point, so will start there.

Cheers,

David