A lengthy answer here.
Question #1 How was it determined the upstream NOx sensor was bad ?
OK I understand they have gone through about 4 iterations that I know of on this side but the ultimate latest & greatest has an NGK sensor tip in it connected to a Bosch solid state box half way up the cable which makes its own computer page for want of a better description. On the back of the box the question is
what is the part number?
Lets assume the replacement it was good and the original was bad, but it
needed SCN coding anyway post install to start shaking hands with the ECM thus speaking the right language .
Now once installed the tech needs to drive the vehicle for about 30 miles to see if the car is re-genning automatically and that the
upstream NOx sensor is transmitting NOx info in LIVE DATA..
If there is next to no tangible signal there is a likelihood of an air leak into the "zorst system upstream, or the Cat is plugged up. Then test the
pressure readings on the EBP and diff pressure sensor in HPa.
So its at that point you return to the shop and investigate why!.
Question/statement #2.
When doing the road test and upstream is seen working what is the r
ear NOx sensor doing?
Reading off the two figures do a quick calculation and there MUST be at least a
50% of reduction across the SCR cat when the system is seen working .
New sensors and an SCR cat will give more than 75% reduction.
In our case we touch the scan tool and print off the figures as you drive with an assistant proving at least its working.
Seems from your narrative that the two sensors were not SCN coded and after a set of drive cycles the system "sees" that it not speaking the right language to communicate.
Its a bit like trying to date a drop dead gorgeous foreign female and and you cannot speak her lingo with any fluency. Confusion exists ! OMG opportunity lost Mr Smoothy !
Statement & question #3
For the system to reduce NOx it MUST have Adblue DEF fluid pumped into it when required.
So was the DEF pump tested by a bi directional scan tool to confirm that fluid is actually injected into the SCR cat .The pump must generate 5000HPa be capable of backing off the pressure by the return system and see an operating pressure of around 3600 HPa.
These things are vital as well ,as checking the atomized delivery of DEF fluid through the
dosing injector which must not be furred up with crystals of DEF AND that it is of the correct specific gravity .
Now the practical
Yes an O2 socket will fit. Cranked is better and use a good length knuckle bar , don't tickle it !! '
When I know that the sensor is junk I sometimes simply cut the harness at the tip, and and use a double depth 1/2" socket to drop over the top of the sensor to work it out.
Penetrant like Plus Gas might be needed as well as a plumbers MAP gas torch to heat the boss area to make removal a bit easier if its bound up .
Once installed a shop should charge you about???? --well over here I charge $ 250 for the programming and the road test to certify its system functionality and the test print outs go to the customer ands archived on the finished R/O.
Hope that gives you some insight
.All the best
Tuercas Viejas
