Thick white smoke from exhaust

[Nego2403]

Hello all of my fellow frenchcarforum members

I've ran into a problem with my Citroën C3 BlueHdi 100 from 2016.
For some time it has been producing thick white smoke when accelerating. The smoke is so thick that I can't see anything through my rear window. For some time I've had error codes regarding the reductant injection valve being stuck open and some NOx sensor performance issues.

This all started around 20 km after a DPF regeneration. I've tried to erase the codes and they kept coming back. But it wasn't the same codes everytime. After the error codes came on the car stopped smoking from the exhaust. After clearing the codes it's running fine with no visible smoking from the exhaust.

I've read the faults with diagbox and attached them to this post.

The pressure of the urea system is stable at around 5 to 5.5 bar. The level of urea in the tank is around 7 liters. I read the deNOx system in real-time and it says "Operating status of the deNOx system: Urea gauge - pump module stopped with urea solution". What does this really mean? I interpret it as the pump is not delivering more urea to the injector. But this isn't true as it is displaying around 30 mg/stroke.

Do someone know what these errors are coming on for?

[GiveMeABreak]

Hi and welcome

The P2201 fault code is to do with the tightening of the NOx sensor. It may also produce other fault codes. The guidance is to check the NOx sensor and tighten to the correct torque.

[Nego2403]

Thank you.
I haven't replaced the NOx sensor, can it loosen itself over time? Do you know what the tightening torque is for the sensor?

[GiveMeABreak]

Pop your VIN up (Automasked on post submission) and I can see if I have the torque values for this engine.

[Nego2403]

The VIN is VF7**************[VIN obfuscated, can be read by forum staff]. Thank you in advance!

[GiveMeABreak]

Ok, so I don't have the Exhaust torque info for this particular model.

On my DV5 engine the NOx sensor tightening torques are 5 daN.m.

[Nego2403]

Okay thank you. Is this error due to a loose or an overtightened sensor?

Regarding the smoke is it possible that too much injection of urea in to the exhaust could cause this?

[GiveMeABreak]

Too loose.

As far as the white smoke is concerned - that can be down to condensation in the exhaust that is being evaporated as the engine warms up.

You may smell a slight amount of Ammonia from the exhaust as this is normal with UREA, but if is is very strong then that may be an over-dosing issue.

The other reason for white smoke is coolant or water getting into the combustion chamber. So this should clear up after a few minutes - if not then you may need some further investigation / check for a head gasket leak or other.

[Nego2403]

The weird thing is that after the codes went on the smoke cleared up and nothing was visible coming from the exhaust.

Another thing I've noticed is that the exhaust tip is full of white powder which looks like crystallized urea. Don't know if this gives any other indications of the problem. Of what I know AdBlue is made up of more than 60% water which would be my best guess as the coolant level is consistent and has not dropped for 3 days now. I've checked the level each time I've used the car.

Could it be a possibility that too much urea is injected due to the loose NOx sensor?

[GiveMeABreak]

Just a little info:

On your vehicle you have Euro 6.1 Emission Standards. The Urea solution consumption was consistent with the Euro 6.1 emission control standard, but was increased and became variable for Euro 6.2 standards (see second diagram). So your Adblue injection rate should still be consistent. But if the NOx sensor is playing up it may be injecting for longer than is necessary if the measurement data is out.

Diagram of DW / DV engines compliant with the Euro 6.1 emission control standard (Private vehicles / Light commercial vehicles).

Key:

(1) DeNOx absorber.
(2) Temperature sensor.
(3) DeNOx catalyser.
(4) Particle filter differential pressure sensor.
(5) NOx sensor.
(6) Urea reservoir.
(7) Particulate emission filter (pef).
(8) Urea injector.


Diagram of DV engines compliant with the Euro 6.2 emission control standard (Private vehicles / Light commercial vehicles).

Key:

(A) Urea solution injection.
(1) DeNOx absorber.
(2) Temperature sensor.
(3) DeNOx catalyser.
(4) Particle filter differential pressure sensor.
(5a) Upstream NOx sensor.
(5b) Downstream NOx sensor.
(7) Particulate emission filter (pef).
(8) Urea injector.

For Euro 6.2 engines, they incorporated an additional NOx sensor upstream of the catalytic converter for more reliable control of the quantity of urea solution to be injected. For the new DV5R engine family, positioning the deNOx assembly (consisting of the deNOx (DOC) absorber, the deNOx catalytic converter and the particle filter) just below the turbocharger made it possible to remove the additive mixing function of the particle filter.

So in my case with the 6.2 Euro standards, the Urea injection is both increased in capacity and is variable to account for different driving conditions.

I noticed last month when I looked in my engine bay and noticed the catalyst and Adblue injector right in front of me!

[Nego2403]

I've heard a lot of problems with the Peugeot and Citroëns using the 6.1 euro standard deNOx system. Many problems were with the tank and pump assembly. Hope it's not my case. I'll try tightening the NOx sensor and probably run a heating test as one of the trouble codes was something regarding the heating of the sensor. Thank you for the nice diagrams and explanations!

[Nego2403]

Update to the case. I've been under the car and tried to loosen the sensor but it wasn't budging it was rusted and almost welded itself to the exhaust...

What could be the cause of the error if it isn't a loose sensor?
There was no visible damage to the cables of the sensor.

[GiveMeABreak]

Yes, the earlier systems did suffer from the unvented cap issue in the Adblue tanks - this could lead to pump failure and a replacement tank as the pumps are part of the whole assembly. The other issue was the components used in the earlier tanks had too many metallic components and of course the Urea solution caused these to rust, so later tanks have more plastic parts in to help prevent this. Then there were issues of the wiring harnesses getting burned and the sheathing becoming worn on the exhaust - so that led to shorting out. Then there were injector failures and leaks - but these were not unique to PSA of course.

If you are getting consistent white smoke and it's not the coolant, then it could well be over -injection of Urea. Your only recall is to get it diagnosed at the dealer - they should start having enough knowledge of the symptoms and failures now from those earlier systems.

[Nego2403]

I've checked and my car is after the recalls so hopefully it's not with one of the bad components.

The white smoke dissappears when the codes come on. I suspect that the urea system is disabled when the codes come on and this could probably explain it. There hasn't been any smoke since I cleared the codes. Coolant level is fine.

I had an urea injector valve stuck open error which concerns me. I'll check the injector and see if it's clogged. Couldn't the NOx sensor readings be all over the place if too much urea was injected into the exhaust e.g if the injector was stuck open?

[Nego2403]

There was an error on the urea injector sometimes it would get stuck. I tested the injector and randomly it wouldn't open or close. I tried cleaning it but it didn't work. The coil was probably toast. I replaced the injector and the problem went away. The car is still running fine after 30k km.