C3-09 electrical problem (ESP/ASR/OIL PRESSURE)

[Naesstrom]

Hi and greetings from Sweden!

I bought my wife a C3-09 VF7**************[VIN obfuscated, can be read by forum staff] this summer and it worked great... until... It started spitting out an error message with ESP/ASR problem, followed by LOW OILPRESSURE and then it refused to accelerate, Turning it off and then starting again works just fine and between the faults it's going great!

After doing a whole bunch of Googling I found out that it seems to be a somewhat usual problem on some of the C3's between 2008-20010 and is from some kind of electrical problem in the BSM.
Found a "new" one on the local scrapyard but the numbers are a bit different although they look identical.

This is mine C3-09:


And this is the scrapyards from a C3-14


Can I use the newer one in our car or wont it work? I could maybe find one from the same year but then I'm afraid that the problem will come back in a while anyway. We're going on a 1000km drive on tuesday and don't want to get stranded on the highway

btw, this is a good video of how to replace it if someone needs to do the same, reading the comments (with google translate) makes it look like changing the BSM is a miracle cure that fixes almost all problems

[ozvtr]

The BSM is basically a relay box supplying power to some components on the outside of the car, like the wipers and the lighting.
It also supplies power to engine bay components like the engine ECU and the ABS ECU (and others).
For the most part, power comes into the BSM and is split up into fused sub-circuits to isolate faults if they draw too much current. The fuse for that circuit blows and it doesn't interfere with power to other things.
Some of the power is supplied and cut by relays (electric switches).
Most of the relays PSA uses are not up to the task, and worst of all they are not able to be replaced! They are soldered onto the PCB and are not "user serviceable". IMHO the contact rating (the amount of current the relay contacts can handle) is poor. Failures throughout the PSA range due to bad relays are common.
If replacing the BSM turns out to be "a miracle cure", it's most likely because one of the relay contacts were burnt out and it wasn't supplying power to...whatever.
I have also seen fuse holders melt due to poor contact and high currents.
The next most common fault is corrosion of the electrical contacts in the connectors. Looking at your BSM the contacts look good. So it's unlikely to be that.
I know there are variations between similar looking BSM's but I don't know if that would impact installing it in your car. Ideally you would get matching part numbers.
Generally speaking if a device is incompatible, the electrical connectors will not fit. The pre-facelift and facelift BSM's have totally different connectors because the systems are completely incompatible. If the BSM's were not compatible you would probably find the connectors would not fit, even if they looked the same. Usually the engineers would make the connectors a completely different shape and colour.
And without further evidence, I cant say if the BSM is actually your problem.
Do the low oil and ABS warnings come on at the same time?
I do not have access to the "all CAN" (facelift) C3 circuit diagrams so I cant do any diagnosing for you, sorry. But from what I do know about the systems, I don't know of any connection between the oil pressure switch and the ABS/ESP module. The oil pressure signal (ground/no ground) does go through the BSM but it's processed by the BSI in the glove box. The signal just goes into the BSM on one connector and out to the BSI on another connector!
The ABS module typically gets its power from the ignition switch and the BSM only supplies power to the ABS, it doesn't process any signals. Again, it goes through the BSM and a fuse then straight out to the ABS module. It's possible on the facelift BSM they are in the same connector but as I said before, the connectors look good.
Sorry but without access to the facelift circuit diagrams this is all just speculation. I am not saying it isn't the BSM, I just have no proof either way.
Just a guess but I would say the low oil pressure warning is putting the engine in limp mode.
The ABS system is an "auxiliary" system and will not cause the engine to go into limp mode.
The fact that you can turn the ignition off and then on and the fault is gone shows the faults are transient. But the faults are logged as 'on', until the system is reset, despite the fault going away while the engine is running.

[GiveMeABreak]

You need a proper diagnostic first with Diagbox before swapping out any parts.

When you get the fault codes (if any) pop them up here and we'll be more able to assist. BSM (the engine fuse box) must be the identical part number, regardless of how they look. These are designed for specific models, engines and options and are not interchangeable.