2016 Citroen C4 Grand Picasso P16A7 and P2047

[RichardW]

4 bar is the min it reads, and means there is no pressure. Once it gets to the enable stage it should increase to 6 bar, then drop to about 5.5 when injection is authorised. I suspect if there is a fault then it won't even try to pressurise. There is only 1 NOx sensor downstream on these. Best bet for wiring diagrams is to register with service box, and then pay the €9 for an hour's access and grab as many wiring diagrams and service procedures as you can.

[Tom309]

NOx sensor readings 0 & 20ppm, I think that that is what I get.

The pump remains at 4 bar until the deNOx catalytic converter reaches 175C (middle line on print-out shows only 15C).
It usually takes about 5 miles of driving to get to temperature, then as Richard says it gradually drops in pressure as the fluid is used.

If the injector is not working, it will stay at the 6Bar. The line to look at is the DeNOx system bleed status - if all ok it will change to "average consumption"
When I've had my open-circuit injector (blown fuse), I've heard my pump run to de-pressurise the system at the end of the journey. So I would say it does pressurise with a faulty injector, but I haven't actually checked.

Note that if you look at this thread there is some more info on operation of the Adblue tank operation:
viewtopic.php?p=726806#p726806

[Ste2187]

On the "if I introduce a - to the white cable the urea injector works…." was that this with the injector wiring plugged-in and the ignition on?
As engine ecu monitors the switched side of the injector I would have expected the error to change from "injector open circuit" to "injector short to earth". Did you see this? No it still said open ciruit with the a light bulb between pin 1 and 2 and an extra ground on the white cable.
I would suggest the following to see if the monitor still works:
Remove F4 and the injector electrical plug. Measure the voltage to chassis earth to each of the connector pins. I would expect pin 1 to be 0V and pin 2 (which I think is the white wire) to be about 2 to 3V. With the fuse removed, I would expect in to be below 5V.

f4 removed, igition on, injector unplugged, 1&2 to earth 0, 1&2 to battery + 9v, pin to pin 0v

If pin 2 is below 5V, connect it to chassis earth by a test wire, turn on the ignition and check that Diagbox now shows "short-to-earth" in place of open-circuit (I have done this test on my car).
White cable to ground still reads open circuit

Measures pin out on injector plug to ecu plug - both reading 0 ohms and 1 ohm between cable

[Tom309]

"if I introduce a - to the white cable the urea injector works"…."No it still said open ciruit with the a light bulb between pin 1 and 2 and an extra ground on the white cable."
-So the injector was not fitted, it was the light bulb that turned on/works?

"f4 removed, igition on, injector unplugged, 1&2 to earth 0, 1&2 to battery + 9v, pin to pin 0v."
Something is not right about these voltages. The earth to battery will be 12V, so if battery+ to pin1 or pin2 =9V, then pin1 or 2 to earth must be 12-9=3V.
Please would you re-check these voltages. On mine I had Pin 1 to chassis earth: 12.2V, Pin 2 to chassis earth: 3.4V, Pin 1 to Pin 2: 8.7V

On Diagbox should now show "short-to-earth", I forgot to mention that you would need to re-run the fault finding screen to check for the new fault. I would do it on the engine ecu fault finding, not the global test to save time

Previously when you measured the injector what resistance did you measure?

[Ste2187]

Right................................... so i think i have finally found out what the issue was with the car tonight, after getting the results i had earlier which have been baffling me, i then starting to think i had an issue with my ecu, i took the ecu out to have a better look at the ecu terminals, i was about to try and take aprt the ecu so i could test the plug connection to the ecu but i thought id better take a closer look at my ecu plug, so i stripped it down and thought id check to see how tight the terminals were, and noticed with a dressing pin that about 6 of them were lose, i removed the terminals from the ecu plug, used a dressing pin to bend the terminals back making them tight again ( i wonder if someone had jammed something in the ecu plug previously for measuring the urea injector and other parts of the wiring loom as this has 100% been previously work on before) i then used contact cleaner and fitted the ecu plug in and out a few times.
i then put a 21w bulb in the terminals of the urea injector and fired up diagbox, reset fault codes and then the dredded urea injector control fault came up, but i noticed that instead of the fault being open it was now a short, i quicky removed the urea injector, plugged it back into the loom and done and actuator test and finally at last it worked with no fault codes!!!!
needless to say ive had a beer to celebrate and going to continue putting the car back together tomorrow! its been a very confusing and long winded process but you guys have been a great help with your information and suggestions with what to do and greatly appreciate it, will report back tomorrow with how the reinstall goes

[GiveMeABreak]

Well done, sometimes it is the simplest of things and the pins / connections are often a common cause as detailed in multiple posts, but often looked at as a last resort. Pleased you have it sorted.

[Tom309]

A great result, 10 out of 10 for perseverance!