Citroen C2 - dead electrics - No power to locks, interior light, ignition - everything dead

[Dormouse]

NAPPING. If you do go ahead with the power to F13 only do it for long enough to see if anything powers up. DON'T go any further yet, just come back and tell us what happened or didn't happen. Then we can have a think about going forward and in what direction.
WHEELER. Can you have a think about precisely how to go about Canbus tests.
cheers everyone.

[wheeler]

I will put something up later (but may no be till this evening) on checking the CAN bus. I’ll go through the diagrams & get some pin numbers. Do you by chance have access to an oscilloscope?

[Dormouse]

Not nowadays. But I can use one. I do still have a very old but precise mirrored Megger which, if used properly, is very good in cases like this.

[napping]

Do you by chance have access to an oscilloscope?

No, just a multimeter or two.
NB. If the consensus is the BSI is at fault, I can send it away for testing.

[wheeler]

At least confirm the CAN lines are ok before sending the BSI away.

[Dormouse]

Testing and repair will be easier if you can narrow down the issues and report the items that are working. The tester will be in the same boat as the rest of us.

[napping]

I think you should check the CAN BUSes under all circumstances because, if the buses are not working you will get nothing out of the other ECUs, let alone to the BSM.

Unsurprisingly and not sure if this is relevant , but when I connect an OBDII reader it powers up from the socket and can't find anything to connect to.

[napping]

One question I have... Where the locking relays on the BSI go to fuse F2 in the engine bay, does F2 connect to earth?

BSI, glove box. Yes looks like it. However, I bet F2 has a lower value than F15. F15 might be connected to other circuits but F2 is only protecting the door lock circuit.

I want to check the rating for F2 that protects the central locking circuit, but according to my fusebox diagram there isn't one on the BSI glovebox. There is an F2 on the BSM engine bay fuse box but my diagram says that's for the horn. Can anyone clarify where to find F2?

[wheeler]

OK the easiest way to check the CAN lines is checking the resistance across pins 7 & 14 of the diagnostic socket, you should get 60 ohms (give or take a couple of ohms).
You can check the voltage of the CAN high & low here too. Measure the voltage between pin 7 & earth then pin 14 & earth. You should get 2.5 V on each however I suspect you may not get this as we suspect the BSI has not woken.
At least if you get the 60 ohms we can say the wiring of the CAN circuit bus is likely OK.
Can i just check the history of this fault? was everything OK one day then the next you went to start it & it was like this or did it conk out whilst driving? Was any work done to just prior to it happening/

Just a thought but does it has something to do with the immobiliser ?

This is definitely not an immobiliser issue. All the immobiliser does if it doesent unlock is stop the injectors operating, The starter motor would still turn & attempt to start, in this case we have an almost complete loss of electrics.

[napping]

Can i just check the history of this fault? was everything OK one day then the next you went to start it & it was like this or did it conk out whilst driving? Was any work done to just prior to it happening/

It was running perfectly when last parked up but wouldn't unlock etc. on return a few days later.
That said, as I mentioned in my initial post, this is the second time it has had an electrical failure.
The history is as follows;
After lockdown last year the car battery wouldn't hold much charge. The battery was replaced as the old one was over 4 years old.
Then I found the front left suspension coil had snapped so fixed that over a month and this is when the locking stopped working, whilst the car was jacked up and not being used.
Whilst checking fuses and checking continuity to the engine ECU the electrics bounced back and I was able to run a BSI reset. At that point, the car was again starting fine and all electrics were working.
The car drove for a couple of months without any issues whatsoever. Then, after parking it up for a week, it wouldn't unlock via the remote and I had to use the key to get in. So that's how we got to where we are now.

[Dormouse]

OK the easiest way to check the CAN lines is checking the resistance across pins 7 & 14 of the diagnostic socket, you should get 60 ohms (give or take a couple of ohms).
You can check the voltage of the CAN high & low here too. Measure the voltage between pin 7 & earth then pin 14 & earth. You should get 2.5 V on each however I suspect you may not get this as we suspect the BSI has not woken.
At least if you get the 60 ohms we can say the wiring of the CAN circuit bus is likely OK.
Can i just check the history of this fault? was everything OK one day then the next you went to start it & it was like this or did it conk out whilst driving? Was any work done to just prior to it happening/

Just a thought but does it has something to do with the immobiliser ?

This is definitely not an immobiliser issue. All the immobiliser does if it doesent unlock is stop the injectors operating, The starter motor would still turn & attempt to start, in this case we have an almost complete loss of electrics.

So. Are the voltages and resistances the same for several onboard systems or is it model specific?

[wheeler]

As far as i know the CAN protocol is pretty standardised across all makes & models. On the high speed CAN each of the end of line control units (In this case the BSI & the injection ECU) each have a 120 ohm termination resistor in them giving the CAN bus circuit a total resistance of 60 ohms. I believe its the same with the voltages.

[Dormouse]

So checking the CAN pins 7 & 14 for resistance and voltage are quick and simple for Napping to do at the Diagnostic Plug pins.

[Dormouse]

I think you should check the CAN BUSes under all circumstances because, if the buses are not working you will get nothing out of the other ECUs, let alone to the BSM.

Unsurprisingly and not sure if this is relevant , but when I connect an OBDII reader it powers up from the socket and can't find anything to connect to.

This proves power is reaching the Diagnostic Plug, giving credence to Wheeler's desire to check the CAN voltages and resistance as a simple diagnostic check.

no Canbus, no ECU comms, no readings

not quite that simple - it won't pinpoint the fault but it is one more step forward.

[Dormouse]

According to Wikipedia's "simple" explanation, several BUS (connecting systems) networks can be present in vehicles.

Yours will have a CAN and a LIN network plus the "simple" wiring harness/fuse boxes which is another "simple" connecting network separate from but working in tandem with the CAN and the LIN.
All three are separate but linked and are all contained together in what you see as a "wiring loom and boxes". Confused? Join the club. That is why you can power up individual components like pumps, relays or lights with power leads but not get the entire system to work. When you are testing you are often working in one network (say wiring harness) but not in the others. Once you understand the need to treat and test the "networks" separately, and in stages, along with the components they serve then you are on your way to being able to repair them.
My suggestion of powering F13 is not in the same network as Wheeler's CAN pin tests or exactly like OZVTR's test points but each will give information about the state of the networks they are in. Your power at OBD meter is another clue. The more clues, the nearer you get to the fault (or faults).
The problem with modern car fault tracing is that there is more visualising, testing and understanding before the spanner work starts, but once the problem is understood the manual dexterity takes over.