citroen c3 'decides' it doesn't want to start

[chris dobo]

I have a citroen c3 'desire'.( 07). A few months ago it wouldn't start. Just the click of the key , and nothing. Obviously i checked the battery and then assumed it was the starter motor/solenoid. i replaced the starter - still wouldn't start. I noticed that it would bump start and I also noticed that if I 'hot wired' it- reached around the back of the engine and touched a wire directly from the battery to the solenoid- it would start first time. Having got it started, if I continue to drive for about quarter of an hour or more, when I turn it off it will happily start again on the key and continue to do so for the rest of the day. However, if I leave it until the next morning for example its back to square one and I have to hot wire it again. In fact that's how i've been driving for the last few months. Out of shear frustration and to make life a bit easier for myself I attached an extra wire from the solenoid to the battery via a switch I installed inside the car under the dashboard. When I do try and start it on the key I can hear a couple of relays clicking under the dashboard coming from the direction of 'body control unit' and I'm starting to think the car might be deliberately stopping me from starting it for some reason? There's no information or warning given on the display and I imagine it would come up with something rather than just stop working without explanation. I replaced the under the bonnet fuse box ( thought it might be a faulty relay in there) it did start afterwards but the next day it was the same as usual. I have a cheap plug in code reader - that came up with nothing as well. Is it worth replacing the body control unit with a clone? or is there something i've missed? This week i've had to replace the head gasket after finding oil in the coolant. Now I'm starting to think the electrical problem might be related and the car 'was' trying to tell me something all along.-Or am I crediting the car with more intelligence than it deserves and these two problems are totally unrelated? I did look at the Haynes manual wiring diagram but it doesn't give that level of detailed information. This is the first car i've ever had with any kind of computer in it, i've been driving much older cars up until now. As you can probably tell by my persistance I hate being beaten by a car so any help would be much appreciated.

[GiveMeABreak]

A proper diagnostic with Lexia is your best bet to determine what is or isn't happening. Lexia can run live data to see what is happening when you try to start the car. Replacing components is a waste of money unless you know where to start looking.

[CitroJim]

Chris, you'll need to consult a wiring diagram to see how the solenoid is fed... I can't imagine it's as clever as we'd like to think it might be!

This very issue was once very common on some V6 Xantia and XM models and it was down to high-resistance contacts on the ignition switch...

Another potential cause, if it's an automatic, is the start inhibit circuitry which prevents a start if the transmission is not in park or neutral.

Given a donation and your VIN Number forum staff may be able to offer you a wiring diagram... All should then look a little clearer...

[wheeler]

What brand of starter did you fit? If it was a ECP RTX brand I wouldn’t rule out this being faulty.
Full CAN PSA cars like this one use a low current ignition switch, it’s literally just a signal & there is practically no load on the switch, the wires at the switch are tiny. Obviously it could still fail but so far i’ve yet to see one fail.
There is a 5 or 6 way single row connector on the under bonnet fusebox, pin 2 od this connector should be the output to the starter solenoid.

[ozvtr]

Full CAN PSA cars like this one use a low current ignition switch, it’s literally just a signal & there is practically no load on the switch, the wires at the switch are tiny. Obviously it could still fail but so far i’ve yet to see one fail.
There is a 5 or 6 way single row connector on the under bonnet fusebox, pin 2 od this connector should be the output to the starter solenoid.

Through fuse F8 and relay R8. Relay R8 is driven from the electronics of the BSM. So potentially a faulty relay R8? I would check the integrity of the electrical connection of fuse F8 too. I have seen fuse holders in the BSM melt from high resistance electrical connections. But the operation of the starter is intermittent, so it's unlikely to damage the fuse holder. But you never know.

Pin 2 of the 5 way yellow connector goes to the starter solenoid, BTW.

[CitroJim]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...

Madness...

[Michel]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...
Madness...

Jim, the horn on my German motorcycle is CANbus. I replaced the horn with a louder, non-standard item recently and had to buy an adaptor to fit it.

[wheeler]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...

Madness...

Stops the ignition switches burning out though

[CitroJim]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...

Madness...

Stops the ignition switches burning out though

Very true!!!

[ozvtr]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...

Madness...

There is a line from the ignition switch to both the BSM and the BSI (at the start position). I surmise that the starter relay is not directly driven by actions from the CAN BUS. However I do know that the relay (R8) is driven from the electronics of the BSM and not directly by that ignition switch wire. I have a member over on the C3 forum that (co-indecently) has a C3 where the starter will engage, randomly, without the key even being in the ignition lock!!
Could be an interlock to stop the starter engaging while the engine is running? I know that the BSM cuts power to the fuel pump if the engine stops running (from data over the CAN BUS). So it's not a big stretch to think the BSM stops the starter relay if the engine is running. I have the CAN-VAN platform so I cant experiment. Oh...and it could stop the ignition switches burning out too!

The only fly in my "theoretical ointment" is; why would the BSI need to know when the engine is cranking (I.E. the ignition switch is turned to 'start')? In the CAN-VAN cars the BSI is not connected to the 'start' contacts of the ignition switch! I know that there are a lot of "cross checks" done between the BSM and BSI on the all CAN systems that are not done on the CAN VAN cars?!

[chris dobo]

A proper diagnostic with Lexia is your best bet to determine what is or isn't happening. Lexia can run live data to see what is happening when you try to start the car. Replacing components is a waste of money unless you know where to start looking.

Thanks Marc. A mechanic told me to replace a crankshaft sensor. Having done this today it made no difference. So 'Yes' it definitely is a waste of money.

[chris dobo]

Chris, you'll need to consult a wiring diagram to see how the solenoid is fed... I can't imagine it's as clever as we'd like to think it might be!

This very issue was once very common on some V6 Xantia and XM models and it was down to high-resistance contacts on the ignition switch...

Another potential cause, if it's an automatic, is the start inhibit circuitry which prevents a start if the transmission is not in park or neutral.

Given a donation and your VIN Number forum staff may be able to offer you a wiring diagram... All should then look a little clearer...

thanks Jim, having replaced the headgasket, the no crank no start issue is still there so I guess the the two issues are not related. It's at least nice to know the car doesn't know more than i do. lol. Its not an automatic btw so i can rule that. i shall look into the high resistance contacts idea you suggest.

[chris dobo]

What brand of starter did you fit? If it was a ECP RTX brand I wouldn’t rule out this being faulty.
Full CAN PSA cars like this one use a low current ignition switch, it’s literally just a signal & there is practically no load on the switch, the wires at the switch are tiny. Obviously it could still fail but so far i’ve yet to see one fail.
There is a 5 or 6 way single row connector on the under bonnet fusebox, pin 2 od this connector should be the output to the starter solenoid.

Hi Wheeler , thanks for your advice. Im not sure of the make of the starter motor but I;m pretty sure it isnt the issue. If I connect it directly to the battery and by pass the cars electrics it starts first time- thats how ive been starting the car for the last few months. I think i know the 5 or 6 way connector you mention. It didnt make a lot of sense to me . it was live when even when I didn't turn the key and it didn't make the starter work. At that point i realised i was completely lost as to how it all worked.

[chris dobo]

Full CAN PSA cars like this one use a low current ignition switch, it’s literally just a signal & there is practically no load on the switch, the wires at the switch are tiny. Obviously it could still fail but so far i’ve yet to see one fail.
There is a 5 or 6 way single row connector on the under bonnet fusebox, pin 2 od this connector should be the output to the starter solenoid.

Through fuse F8 and relay R8. Relay R8 is driven from the electronics of the BSM. So potentially a faulty relay R8? I would check the integrity of the electrical connection of fuse F8 too. I have seen fuse holders in the BSM melt from high resistance electrical connections. But the operation of the starter is intermittent, so it's unlikely to damage the fuse holder. But you never know.

Pin 2 of the 5 way yellow connector goes to the starter solenoid, BTW.

I took all the fuses out and checked them when i replaced the under the bonnet fuse box - this also didn't solve the probelm. I couldn't find any relays, I think they are all inside the sealed body of the fuse box. This was one of the things i tried quite early on and gave up when i couldn't find any removable relays- which was frustrating. i also took all the maxi fuses out from underneath the fuse box, nothing wrong with them either. Im afraid.

[chris dobo]

I am staggered that something as straightforward as operating a starter solenoid should be totally unnecessarily complicated by use of a CAN bus...

Madness...

That is exactly how i felt about it! I've been through several phases of frustration with this probelm one of which was a totally irrational and unjustifiable xenophobic hatred of French electricians. I think the fusebox or something had 'Siemans' written on it. When i looked up the company on line I discovered they were actually a German company. At this point I realised racism isn't very helpful when it comes to fixing a car. Like I said in my original post I by passed everything and put wire directly to the starter motor and connected it to a switch on the dashboard- Even this was not as straight forward as it sounds as I had to somehow get through the firewall/ bulkhead - With half a bottle of fairy liquid as lubricant i eventually managed to get the wires through the rubber gromit for the bonnet release cable.