DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

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DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

I got the check engine light today, together with a "Urea" light and a message stating the Urea system had a fault. This was shortly after I'd seen puffs of steam while reversing, possibly related?
I've filled up the AbBlue, it needed 10 litres, and it's only done around 4000 miles since the last time I brimmed it. I'm wondering if this is excessive usage? Seems it to me.
I've connected up Diagbox and got a full print of all messages, attached as images below...
Diag1.png
Diag2.png
Diag3.png
Diag4.png
Then I cleared the fault and have been for a 10-mile drive. All appears to be OK, no lights came on. But I did notice an ammonia smell when reversing and can smell it in the fumes when I stuck my nose over the exhaust, after this test run. I don't normally sniff the exhaust, but I doubt this is normal.

As it happens it's going in the local garage tomorrow anyway, for an early MOT. If there are things that can be fixed then I'm sure they'd be capable. I read somewhere on another thread about a dealer campaign for a sensor coming loose - could it be as simple as this? That's the sound of desperate hope, I know these sort of issues tend to be expensive.

All help, good or bad news appreciated! Thanks.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by wheeler »

An you see any urea leaking around the pipework or injector? It’s normally quite obvious as it crystallises around the leak.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

I haven't seen any on the driveway so took this as a sign it's not leaking. But... I've since seen a YouTube video showing that it had all got caught by the undertray and crystallised there. So it's entirely possible it is leaking. I went for a drive today and tried to look down the sides of the engine after, but the 2.0 HDi pretty much fills every corner of the engine bay in these things, partly due to that very slopey windscreen being partly on top of it.

But to my simple, unqualified (and happy to be corrected) mind, the fact that the sensor is reading a pre-treated (upstream) NOx level of 32768 is hopefully a clue. My background's in computing, not cars, and I know that this specific number is the maximum value of a 16-bit signed integer. In other words, the reading is off the scale. I wasn't driving a rally at the time, I was doing 50-ish on cruise control. So you'd expect whatever level it was at to be within the range of the sensor.

Also the exhaust smells of ammonia.

My theory is that the sensor is falsely telling the system that there are levels of NOx in the fumes that are sufficient to kill half the world, so it's spraying in the AdBlue at its maximum possible level to try and counteract it.

So I'm willing to blow the cash on a sensor unless anyone has a better theory. I've submitted a part number request, hopefully it's slightly less than the cost of a new car.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by RichardW »

I clocked the upstream Nox, that's definitely not right!
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

Thanks, glad to be reassured it's definitely not normal.

Nerd knowledge: 32768 = 2 to the power of 15. In a 16-bit signed integer one bit is reserved to indicate whether it's positive or negative, leaving the remaining 15 to indicate the value. I knew I recognised that number as soon as I saw it, 32768 is the absolute maximum value it is capable of recording.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

I had wandered off onto the part numbers requests thread, and have got 3 different diagrams of the inner workings of the system.

I can see the downstream sensor, but can't see the upstream one. The sensor on the unit before the AdBlue injector is called a Temperature Sensor. So, unless it has hidden NOx sensing abilities, it looks like there isn't an upstream sensor at all.

Is it possible that there simply isn't one, and that Diagbox or the car computer is putting in the default maximum value of 32768 to indicate that it doesn't exist?

Meanwhile, it passed an MOT after I'd reset the error and made the yellow light go out. So they obviously don't test for excess ammonia. Today, the day after the MOT, it's appeared again. I'm guessing after probably 100km or so.

I did discuss it with the garage, he suggested a DPF regen, says it's all part of the same thing so could be affecting it. I guess if it's causing back-pressure then all kinds of crazy things could be happening. But it costs nothing to try, other than time and diesel. Tomorrow I'll reset the error again, run a DPF regen and see what happens - but I think it's likely to reappear.

Unless anyone has any brighter ideas my next step will be to start firing the parts cannon until it's fixed. I'll buy a new injector and downstream sensor, get them both swapped at the local garage then do whatever reset procedure is needed. Ebay prices for apparently genuine parts are roughly half to a third of Citroen list price so will get them.

The approach will be professional spanner operation, with DIY mouse-clicking.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by GiveMeABreak »

The NOx sensor is intended to measure the overall volume of nitrogen oxides (NOx) and the mixture of the exhaust gas downstream of the deNOx system. This is the one in my vehicle:
denox.PNG
(1) NOx sensor.
"a" 5-way grey connector.
"b" DeNOx system ECU.

This is how it works:
denox b.PNG
"c" Exhaust gas inlet.
"d" Oxygen content measuring chamber.
"e" Measuring electrodes.
"f" Nitrogen content measuring chamber.
"g" Reference exterior air.
"h" Reference chamber.
"j" Heating resistor.
The NOx sensor incorporates measuring chambers and a reference chamber which measures the oxygen content of the ambient air.
The electrodes enable the NOx sensor to draw in the oxygen in the exhaust gas.
The oxygen in the exhaust gas is drawn in by the oxygen sensor by a suction current "ip1" and is retained in the measuring chamber "d".
The NOx sensor compares the oxygen content in the measuring chamber "d" with the oxygen content of the reference cavity "h".
In order to obtain a lambda of 1, the oxygen content of the measuring chamber "d" must be equal to the oxygen content of the reference cavity "h".
The value of the pumping current is linked with the flow of oxygen originating from the exhaust gas, necessary in order to regenerate the oxygen in the measuring chamber "d" and have a lambda of 1.
When lambda is higher than 1 in the measuring chamber "d", the pumping current is positive, the excess oxygen contained in the measuring chamber is taken off to be sent to the exhaust gas.
When lambda is lower than 1 in the measuring chamber "d", the pumping current is negative, the oxygen which is lacking is taken from the exhaust gas and sent to the measuring chamber.
If lambda is equal to 1, the NOx sensor delivers a voltage of 0,45 V.
The output electrical signal proportional to the oxygen content is obtained by measuring the current "ip1" required by the pumping cell to regulate the oxygen content in the measuring chamber.
The second measuring chamber "f" is dedicated to measuring the nitrogen content in the exhaust gas.
The intake current measurement "ip2" provides a proportional image of the nitrogen content in the exhaust gas.
The deNOx system ECU interprets the information provided by the NOx sensor and transmits it in the form of a datastream on the multiplexed network.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

Hello. All makes sense, that's the downstream one. But the diagnostic report includes a reading from an upstream sensor, which has an off-the-scale reading of 32768. I can't find the existence of such a sensor anywhere in the system, so what I thought was a pointer towards the faulty component may in fact just be an indication that it doesn't exist. Perhaps other models do have one, which is why the software includes a measurement for it, which just has a dummy value of 32768 where it doesn't exist.

However, there's lots of good news. I had previously cleared the error, it re-emerged the day after its MOT (phew), but this time it's much more obvious what's happening...
DiagNew1.png
My guess is that the complicated stuff last time was a result of a load of random nonsense happening while it was failing, now it's completely given up. Google indicates, from this site and others, that error U029D 87 is related to the downstream NOx sensor, and that is the part that I ordered yesterday anyway, as part of my "firing the parts cannon at it until it works" strategy. So it looks like the cure is already in the post.

I'd also ordered a new NOx injector before I saw this report, but will still get this changed just as a precaution as I'll be paying someone to jack it up and look at it so it might as well get changed at the same time.

Sensor was exactly £100, injector £60. Both supposedly genuine parts from (non-Chinese sellers) on ebay. Will inspect very carefully when they arrive.

I didn't bother doing a DPF regen, I checked the status and it all looks very healthy - 22% clogged, last 10 regens every 600-odd kms, last one 200-odd km ago.

Do I need to perform some procedure using Diagbox after fitting? Any pointers welcome, it's pretty weird software to navigate, been playing today and there often seems to be 3 different routes to arrive in the same place.
Last edited by NotAnInterestingName on 28 Oct 2022, 12:47, edited 1 time in total.
wheeler
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by wheeler »

There is only one NOx sensor.
After replacement of the sensor you should carry out replacement of the NOx sensor/initialiseation of the De NOx system in diagbox.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

wheeler wrote: 27 Oct 2022, 20:13 There is only one NOx sensor.
After replacement of the sensor you should carry out replacement of the NOx sensor/initialiseation of the De NOx system in diagbox.
Thanks, so the reading from the original report is a dummy value. Owning a DS would be complicated enough already, without the report including measurements from sensors that don't exist!

Ah well, hopefully the end of this issue is in sight. Perhaps this thread may be useful to other confused people in future.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

Currently awaiting parts, but today it decided to fix itself. No yellow light or messages, all apparently well. So we have ourselves an intermittent annoyance then.

When I looked at the back and saw the white crystals below the exhaust it's obvious it's been severely over-dosing on the AdBlue, presumably due to the dodgy sensor telling it to squirt in more and more.

Will get it fixed next week hopefully, then top up AdBlue tank, wash off the white dusty mess from the exhaust surround and monitor to check it stays clean. Although I suppose the exhaust may spew excess for a little while longer if it's full of the stuff.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by GiveMeABreak »

The injector may be faulty, so could explain the surrounding crystallisation.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by Uncle Tom Cobley »

Just had the exact same problems and symptoms on my C4 Picasso Grand.
Turned out to be the urea tank ( low pressure ) I also had a new injector fitted needlessly and my exhaust smelled like boiling ammonia . The car ran with no warning lights on for ten days after having it fitted but it came back on with all bells and whistles only to completely disappear again.
I took my car to my local Citroen main dealer in the end and I got a huge discount from Citroen , so dont be too put off about going . It was £530 for new tank ,diagnostics, labour, ad blue and computer reinitialisation should have been around £1600!
A warning though…As I said all my lights went out too but they assured me the fault was still going on in the background.

Just a heads up on parts….
Give this chap a call .. Lee Busby K.R.P supplies 01384 265250 they are an independent Vauxhall parts specialist but since Peugeot and Citroen have come into the group they sell their genuine parts too and a lot cheaper than the main dealers.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

I can't imagine how a faulty pump could result in too much AdBlue being pumped in? That doesn't sound logical, and definitely hope I don't end up with that being needed. I haven't had any countdown messages about only having x miles left until it won't start, I've seen this reported in other cases where the pump had failed, presumably when it detects a high level of NOx at the sensor or perhaps it detects the pressure of the line to the injector somehow.

Will try replacing the injector and sensor with new genuine parts for £160 + labour , see what happens and will report back.

Even if it is fixed, it's probably going to take a while to clear the excess AdBlue out. I saw an exhaust on YouTube that was literally full with a block of crystals in the space where the injector goes. Will ask the garage if I can have a look after the old one's removed. Hopefully any surplus will slowly dissolve away over time though.

After the yellow light vanished all appears well, I haven't noticed any smells or clouds when reversing as I saw while it was in failure mode. It looks like it's intermittently fixed itself, whatever the cause.

It may be becoming clearer why the previous owner decided to sell! I'm sure it can be sorted though, I still think it's an amazing weird spaceship barge.
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Re: DS5 AdBlue Issues P20EE00 P20F600 P2A0000 P16EA00

Post by NotAnInterestingName »

Uncle Tom Cobley wrote: 30 Oct 2022, 11:35 I took my car to my local Citroen main dealer in the end and I got a huge discount from Citroen , so dont be too put off about going . It was £530 for new tank ,diagnostics, labour, ad blue and computer reinitialisation should have been around £1600!
How old's your Citroen, and did you buy it from a dealer?

Mine's over 6 years old and bought as a private sale. I don't really expect gold star support.