What's This?

DesPicasso · Unread post by **DesPicasso** » 03 Oct 2011, 21:15

On my 2l HDI Citroen xsara picasso does anyone know what the black box above the brown fuel pump relay is? Its the box in the picture below held together with a cable tie.

Unread post by **CitroJim** » 03 Oct 2011, 21:29

Hi Des and welcome

Definitely a bit of an add-on that..

Can you see where the wires go? Their destination may offer a clue...

Do you have a towbar with a grey socket on it? It could be connected with that (sorry, no pun intended?)

DesPicasso · Unread post by **DesPicasso** » 03 Oct 2011, 22:10

Thanks for reply and the welcome

I don't have any towbar or anything additional as far as I can make out. The wires go to all different places but most of them seem to go into the loom. There is an odd purple wire that I traced going over the fuse box and in through the bulkhead so a bit of a mystery.

I did think that this was an add on as I haven't seen it on any other HDI engines on the picasso. The reason I ask this is that after replacing the engine the car started but after a day it started cutting out then eventually died. I suspected the fuel pump relay as it was buzzing intermittently and so replaced it. Initial on replacement of this the car started but cut out after min or so and the new relay started buzzing. The car will not start. Thing is although I plan to check the fuel pump, when this black box is tapped with the end of a acrewdriver the relay stops buzzing but just for a moment. This has made me wonder if its the culprit but without knowing what it is I can't even begin to consider replacing it.

Dippy · Unread post by **Dippy** » 04 Oct 2011, 02:05

CitroJim wrote:Hi Des and welcome

Definitely a bit of an add-on that..

Can you see where the wires go? Their destination may offer a clue...

Do you have a towbar with a grey socket on it? It could be connected with that (sorry, no pun intended?)

Jim's probably correct.

There appears to be a power feed from the battery interspersed with a fuse ?

If one of the other wires links to the alternator warning light connector , the remaining two are to charge the caravan battery / supply to fridge when towing .

The alternator link provides the switching circuit for the relay , otherwise it would drain power to the caravan without the car engine running.

Unless it's really ancient , this relay should be solid - state - no buzz.

Someone may also have used a caravan relay to perform some other mystery function ? - but unlikely.

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 07:43

thanks for that, seems likely but there is no tow bar. maybe i should just disconnect the live feed.

citronut · Unread post by **citronut** » 04 Oct 2011, 08:13

i dont know what that relay is for, but i have always known the brown one as the ECU protection relay,

when you replaced to engine did you re/use your cars original imobaliser electricary,

regards malcolm

DickieG · Unread post by **DickieG** » 04 Oct 2011, 10:04

Where the wires enter the loom can you see any numbers printed onto them? If so it will greatly assist working out what they connect to as with multiplex wiring Citroen print numbers on each wire rather than the old method of using different colour combinations.

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 13:45

I'll have a look for numbers of the wires. Thanks for the suggestions.

The brown relay is a double relay - fuel pump and fuel injectors.

Gibbo2286 · Unread post by **Gibbo2286** » 04 Oct 2011, 13:55

Your added on relay could be for aftermarket accesories such as high power headlights, foglights, twin horns, alarm, etc.

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 14:47

Thanks for that. I'm certain that I don't have any aftermarket accessories fitted but thats not to say that there weren't some in the past and the relay remains.

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 14:51

Would the fuel pump relay buzz if the fuel pump wasn't working? I've heard that the buzzing can be to do with the feed going into it but I don't think I can test this easily.

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 18:40

I managed to trace the wires from the box as far as I can. A purple one goes through the bulkhead as we know and there is a green fused connection to the + feed. There are then two wires that do not go into the loom but go down behind the engine compartment and follow beside the loom tied to it with cable ties. I traced them as far back as the fuel tank when they then disappear above the tank and so I'm not sure where they go. I now suspect that they are going to the fuel pump and explain my symptoms. I won't know until I drop the tank. Still doesnt realy explain why I had problems when I disconnected the + feed though.

citronut · Unread post by **citronut** » 04 Oct 2011, 20:13

sounds like someone in the past has had problems and patched a relay in to sort it,

also as the injection and fuel pump are controled through the ECU im 99% sure the brown relay is still the ECU protection relay, as it is and has been on all other citroens i have seen this brown relay fitted to,

regards malcolm

wheeler · Unread post by **wheeler** » 04 Oct 2011, 20:47

Yeah the brown double relay is a combined fuel pump & engine management system relay.
I'd agree with malcolm here, it's begining to sound like the relay has been fitted to mask a problem with the fuel pump control, start the engine & disconect it, if the engine cuts out a second or two later it will almost certainly be wired to the fuel pump.
Not really a big problem as long as its been done right, ie the signal from the ECU is used to earth the relay, if its not done that way it could be bypassing the saftey featre of the ECU controled fuel pump that doesen't allow the fuel pump to run unless the engine is turning (apart from the initial second or two prime)

DesPicasso · Unread post by **DesPicasso** » 04 Oct 2011, 20:49

it does sound like someone has patched a relay on. I don't doubt that the ECU controls the pump and the injectors but does so through this brown relay. I bought the replacement part from citroen and they describe it as the double relay for fuel pump and injectors. The mystery now is hoe they all interact. My guess is that the added relay is not working.