U1200 81 code?

[Stuart W]

An update on the adblue pump repair possibility.I removed the pump/pressure sensor/ solenoid valve and pressure storage unit and tested them by applying 12v to the motor and solenoid.As expected the pressure shot up over 8 bar since the pressure sensor was no longer connected to the
circuit board.Removing the 12 volts stops the pump and closes the solenoid valve. The pressure remained stored for a long time so no leaks or faults were present.Repeated this test with the pump connected to the adblue pipe to the injector still on the car and pressure storage was good again.This leaves only the pressure sensor as the the suspect and bearing in mind most peoples experience of this adblue failure is that the pump screams out loud and long this also points at pressure sensor failure.The faulty sensor does not register the pressure and so keeps the pump running and struggling to increase the pressure although the pressure is already way higher than it should be.The ecu is being told that the pressure is too low since it gets its information from the same faulty sensor and this is why the system shuts down and gives the diagnostic error message "urea pressure too low"In fact the pressure is too high but the system does not operate the injector until it receives the correct pressure reached message.
I did monitor my suspect pressure sensor output up to 8 bar and it was totally inactive until way past the normal 6 bar.Spare parts for this pump are not available and the sensor is a non standard fitting so I am going to try a mod on this pump.I have bought a standard 3 wire 10 bar sensor and am going to fit it externally by using a short extension to the pump output pipe with a female connector one end and a male connector at the other. A Tee connector in the middle with a pipe and thread adaptor to the new sensor. The sensor cable is wired directly to the red black and yellow cables which were plugged into the old sensor .When the whole thing is back on the car I will update my findings.The sensor and pipes are all available on Amazon/ ebay and cost ony about £25 in all.Certainly worth a try considering how many thousands of pounds this fault has cost us Citroen and Peugeot car drivers over the last few years.

[CitroJim]

Thanks Stuart, a most interesting and valuable update I can see a potential failure mode here: the pressure sensor fails, the pump screams and builds so much pressure and ruptures the tank internals/kills the pump possibly?

Keep us up to date with your progress

[Stuart W]

That is what I suspect is happening in the majority of cases.I will let you know what happens.My only concern is that the new sensor may not track the pressure response of the original one.I will measure the stored pressure.

[Stuart W]

Today I ran the car with the modified pressure sensor on the adblue pump.I cleared all existing faults with diagbox and even the stubborn U1200 81 code has gone.Previously the emissions control warnings would come on after about 4 miles every time I used it..I have only covered 35 miles so far but with no warning lights or beepers and the adblue pump is virtually inaudible when it does run.Also it can be heard running in reverse to relieve the stored adblue pressure after the ignition is off.It has not done that since the fault first showed.I am not going to celebrate yet but intend to do another 60 or more miles tomorrow. Fingers crossed!

[CitroJim]

That's simply superb Stuart Excellent!

[Stuart W]

Well , my modified pressure switch on the adblue pump has now worked happily for over 100 miles without any sign of fault messages or the frequent whining of an over stressed adblue pump.For the sake of spending about £25 I would recommend that any of you with the classic pump failure systems give it a try.If you are diy minded it is a relatively simple mod which could save you a very costly tank replacement.

[KennyW]

Worth doing a how to guide for anybody interested and I'm sure the moderator's will add it to the list.

Kenny

[CitroJim]

Fantastic news Stuart

Worth doing a how to guide for anybody interested and I'm sure the moderator's will add it to the list.

I'll second that!

[Trickiedickie]

Thanks Stuart W. Good work. Great thread!
I do have a question..........as the original pressure sensor has failed you chose to use a 10 bar/150psi sensor as a replacement. Why did you choose it over a 6.9 bar/100psi sensor.