12v Fridge Feed - ?6 Code Fault

[SnJ]

***HELP PLEASE***
Anyone have an idea where the 12v feed from the vehicle comes from when started??
I get a ? 6 fault code when the MH is started up - this means that there is no supply from the engine)

There are 5 wires that are connected to the fridge for 12v supply
Red +12v (provides 12v to fridge)
White -12v
Orange 12v signal feed when engine is started
Purple +12v (powers display on fridge)
Black -12v

Have tested all of these with & without the engine running and the results are this
ENGINE NOT RUNNING
Red/White = 13.32v
Orange = 0v
Purple/Black = 13.32v

ENGINE RUNNING
Red/White = 10.32v
Orange = 10.32v
Purple/Black = 13.32v

Fridge voltage parameters are 10-15v so am assuming that 10.32v is insufficient to kick 12v relay on PCB over to 12v power
Spoken to Thetford direct and have tested the fridge (as suggested by them - great customer service BTW!)
Have completely disconnected the fridge, obtained a brand new AGM 12v battery and wired direct to it .
(RED/ORANGE together and connected them to positive / WHITE to negative)
The fridge works fine - does not display a ?6 fault code
Therefore it's a feed issue
Have pulled & tested all the fuses in the engine bay
Does anyone know where the feed from the engine comes from (alternator??) or if there is a fuse/relay I have missed
Cheers
Rusty

Have attached some screenshots for reference
(ignore the bit on the Norcold pic about the ARP wiring - that's not on this fridge - I used it to see how the block connector plug is wired)

 

[autorouter]

First check the starter battery voltage when the engine is running. The 13.32V on the purple/black wires is coming from the leisure battery not the starter battery. The 10.32V on the red/white wires comes from the starter battery.

There should be a fuse, probably 20A, near the starter battery, to supply the fridge heater. This fuse can get corroded contacts and develop a resistance which causes voltage drop.

However the voltage of 10.32V for the D+ signal from the alternator (orange wire) indicates that the voltage of the starter battery itself is very low. 10.32V is about 5/6 of what is expected, so maybe a duff cell in the starter battery.

 

[SnJ]

autorouter - cheers for the input...Was unsure where the 12v (LC) was sourced from tbh
It's a brand new AGM battery (I bought it on Tuesday)
I'll dismantle the battery box again and ensure the fuses are clean
I'll stick a photo of the battery connections on ...

 

[autorouter]

It's a brand new AGM battery (I bought it on Tuesday)

Is that the starter battery or the leisure battery? Can you measure the voltage of the starter battery terminals (1) engine not running (2) engine running? It's possible the starter battery is flat and the alternator is not charging it. There might be nothing wrong with the fridge at all.

 

[Landy Andy]

Was it working before fitting new battery?

if so I’d double check what work has been done.

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[SnJ]

Is that the starter battery or the leisure battery? Can you measure the voltage of the starter battery terminals (1) engine not running (2) engine running? It's possible the starter battery is flat and the alternator is not charging it. There might be nothing wrong with the fridge at all.

It's the starter battery I have replaced
There is nothing wrong with the fridge
the issue is the feed from the engine.

 

[SnJ]

Was it working before fitting new battery?

if so I’d double check what work has been done.

No it wasn't.
I have fitted a brand new AGM starter battery
It stopped working and I can't find the source from the engine.

 

[autorouter]

I don't know about Autotrails, but the usual setup is
20A fuse near the starter battery
fridge relay in/near the control box - the box with all the 12V habitation fuses etc.
D+ from alternator to the fridge relay
D+ from alternator to the control box on the fridge.

Because the voltage drop is the same for both the heater element and the D+ signal, that points to a possible earth return problem. You could measure the voltage between the fridge power negative (white I think) and a good metal contact on the chassis. It should be zero, obviously, but if there's a bad contact somewhere it might be a couple of volts.

Is it possible that there's a separate fridge negative wire that's somehow not been connected in the process of changing the battery?

 

[SnJ]

autorouter

I don't know about Autotrails, but the usual setup is
20A fuse near the starter battery
fridge relay in/near the control box - the box with all the 12V habitation fuses etc.
(Have checked the fuse and it's fine - however am unsure where the relay is (it may be under the casing i guess))
D+ from alternator to the fridge relay
D+ from alternator to the control box on the fridge.

Because the voltage drop is the same for both the heater element and the D+ signal, that points to a possible earth return problem. You could measure the voltage between the fridge power negative (white I think) and a good metal contact on the chassis. It should be zero, obviously, but if there's a bad contact somewhere it might be a couple of volts.
Took your advice and tested the earth continuity.
Connected the white 12v- cable & chassis I got .5mv
After a process of elimination
connected the starter battery+ direct to the orange D+ wire & started MH up = same fault code
connected the starter battery- direct to the white12v- wire (bypasing the MH earth route) & started MH up = no fault code - fridge operating fine
Therefore the issue is as you suggested of an earthing problem. It may just be corrosion

Is it possible that there's a separate fridge negative wire that's somehow not been connected in the process of changing the battery?
No (only 1 single earth cable to starter battery)

There are only 2 wires that connect into the block for the white wire to connect with so until I get it onto a ramp (Wed this week) I can't see if there is any issue in the chassis rail

Am still hunting for the relay though as that could be the culprit

Have attached some more pics
Cheers
Rusty

 

[autorouter]

Maybe someone who knows about Autotrails or knows about the EM50 control box can contribute a bit of experience here. In the meantime, here's my best guess.

The EM50 is connected to the starter battery by a hefty cable that can supply all the habitation needs at once, including the fridge element power (Fuse 7, 20A). The control box of the fridge is supplied on a different fuse, not sure which one.

The description of the EM50 says
"Provides relay controlled fused outputs for Battery Charging, Fridge, Marker Lights, *Air Conditioner, Electric Step, Awning / Entry lights & *Heater"

So the fridge relay is in the EM50. I think it's not the problem, and if you fix the earth fault that will sort your problem. The negative to the fridge comes from the EM50.

I'm not sure from the diagram, but it appears that it splits and uses two terminals. Standard spade terminals are rated at 15 amps, so they use two in parallel for the fridge feed to avoid them getting too hot. Note that other connections, including the fridge positive, and battery charging from the alternator, also double up the terminals.

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[SnJ]

autorouter
Having tested various bits & coming to the assisted conclusion it's defo an earthing problem, it's going in on Wed to see our auto electrician at work.
It'll be up on the ramps so at least I'll be able to check earthing straps, wiring loom etc.

Thanks for your help & I'll let you know if I find anything else out

 

[pagey]

hi snj did you ever get your fridge sorted out i have the same problem ass you although mine is not an autotrail thanks ken

 

[Jev88]

Older style fuse for fridge in engine bay.... In case it is of use. Green wire in pic.

 

[SnJ]

I think it's an earth fault.
If I connect the fridge to an alt outside 12v source (ie a battery) it will work.
Have an auto sparky looking at it on Wed.

Spoke with Thetford and apparently they will be doing away with the 12v function due t the fact that if the fridge is left shut it will remain cold for approx 8 hours

 

[pagey]

I find this strange as I have exactly the same fault with the save voltage readings it's the 10 volt one I don't understand

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[pagey]

hi snj thanks for the offer of a chat i will catch up with you later in the week

 

[pagey]

Hi snj have you had your fridge sorted yet

 

[MisterB]

if youre convinced its an earth fault, then put a new earth wire in yourself?

 

[pagey]

hi not convinced at all but i have exactly the same 10 volt reading in the same wire on my van snj has an autotrail and i have a sunlight and neither of our fridges work on 12v

 

[jockaneezer]

Think it's been mentioned before that some Brit vans are fitted with seriously undersized wiring. Could be something as basic as simple voltage drop due to the supply wire being too thin for the distance and voltage/amps it has to supply ? As mentioned earlier, might be worth running a temporary, heavier supply/earth to the fridge ?

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[SnJ]

SORTED IT
The EM50 control had shorted out.
It had got wet from a previous owner securing a brolly behind the driver seat and it rested on the EM50 case... Oh Please!!!!!
I removed it when we got the MH, never gave it a thought about damp/wet etc.
Pics are a bit crap
The pics show the white residue and the melted 15a fuse!!! And the power feed under the PCB (which is actually the negative side ghat burnt out)

Have installed a new EM50 and is good again....

Thanks to everyone for commenting and suggestions