Adblue problem - 2015 C4 picasso II B78

[RichardW]

I would assume that means that there is no separate UREA ECU and the function is run but the engine ECU.

[seefourpio]

Looks as though it's probably not a fault then (the thread here ..... viewtopic.php?t=81358&start=15 ...... also suggests that it doesn't have it's own ECU (all done via the Engine ECU). Finger's crossed it just the pressure sensor fault.

Thanks for maintaining such a useful forum!

[RichardW]

Sometimes if the sensor is duff the pressure will read 0 bar - it should say 4 at rest. If you reset the system, then watch the data as it warms up it will get to the pressurising stage, you should hear the pump run, and the pressure should rise to 6 bar. The pump is quite obvious, can hear ours when engine is at idle. If the pump runs but no pressure rise, and keeps running, quite likely it's the pressure sensor. No pump activity, then it's the pump, or electronics.

[seefourpio]

For what it’s worth, I’m updating this with my experiences – but as I write, the problem ‘seems’ to be fixed.
When I first encountered the UREA fault, I put in a dose of Crystal Protect (this existence of which I had been unaware of up to this point). This didn’t seem to rectify the issue though and I had the low pressure fault (and DiagBox was showing the pressure sat at “4”).
I replaced the injector, as it showed signs of leaking and reinitialised - but the fault remained.
I could hear the pump at “ignition ON”. I couldn’t hear the relay test in DiagBox though.
I had a number of long journeys/trips upcoming so I went for a two pronged approach. I got a good deal on a salvaged tank and I also ordered a replacement pressure sensor (with the long 4 to 6 week delivery time).

As my existing tank was pretty full of AdBlue (and a dose of Crystal Protect) I decided to keep the tank and swap over the PCB and associated “gubbins” from the salvaged unit as this was a straightforward swap. I refitted the tank and reinitialised but still no joy – the same fault.
As the counters were being reset ok, I decided to wait for the pressure sensor to arrive before looking at this again. Although, it seemed a bit unlikely (although not impossible) that both units had a faulty pressure sensor.
Anyway, just a few days before the sensor arrived, the problem cleared itself. Initially the UREA and SERVICE lights went out. Stopping and restarting the engine then got the Engine light to go out as well and, so far it’s remained ok!
The car had probably done about 1200 miles since the fault originally occurred and I added crystal Protect, tried the replacement tank PCB and awaited the replacement sensor. I don’t know if the Crystal Protect finally managed to clear a blockage somewhere, or if there is still an intermittent fault that will return – but it’s done 500 miles since the fault cleared and all ok so far – fingers remain crossed.

I’m tentatively chalking this up to the Crystal Protect doing its thing, but I don’t really know what the fault was. At least, if the problem does reappear, I feel much more confident in tackling it thanks to this forum.