u059e: invalid data received from nox sensor a

[muffinmonkey]

Hi,
Recently had the engine light come on with check ad blue message on my Relay 2.0 HDI 2016 van. Error code u059e: invalid data received from nox sensor a

Took it into my local garage who declared "it could be anything" and advised I go down the delete ad blue option.

I'm thinking of replacing the nox sensor myself, thought I'd check if anyone else had a similar issue??

I've pretty much read EVERY webpage that references this error code, not much conclusive info out there

Any advice much appreciated

[GiveMeABreak]

Monkeys - go to another garage!

It's illegal to remove any emissions equipment on public road-using vehicles and they should know that, which would leave you with a vehicle that no longer meets the certification it had - so insurance will be affected and will lead to a lot of potential future issues. Their diagnosis doesn't leave much confidence, although likely to be the NOx sensor, there could be some other possibilities listed below in the description:

Fault Code:	U059E 81
Description of Fault:	Downstream NOx sensor (CAN): Data received invalid. Fault in communication with the NOx sensor: Values invalid.
Conditions for Fault to clear:	At least one of the following conditions must be fulfilled: - After switching the ignition off and then back on - Vehicle in motion
Downgrade Modes whilst Fault is active:	Engine diagnosis warning lamp
Symptoms:	-
Suspect Areas:	Urea pump - gauge module Fuses Urea relay Electrical harness Downstream NOx sensor Electronic control unit Engine management ECU Connectors

There are also a few technical documents for other vehicles with this fault code presenting, that essentially says replace the NOx sensor.

[muffinmonkey]

Thanks for the info I guess a good place to start would be to check the nox sensor is getting power.

Am I right in thinking there is just the one nox sensor on these vans? sitting just after the DPF?

[GiveMeABreak]

I'll need your VIN as there are multiple systems. Please post your VIN in full without spaces - it will be automatically masked from public view after submitting your post & will only be visible to staff.

[muffinmonkey]

Thats great thank you VIN below

VF7**************[VIN obfuscated, can be read by forum staff]

[GiveMeABreak]

Ok, so having checked and this won't be much help, there are a possible 2 versions of system fitted (even with your VIN supplied) so you may have the earlier type of the newer type fitted.

As the later diagram was produced in 2021, which shows both upstream and downstream sensors for stricter emissions controls, I suspect you may have the older system that has only the one NOx sensor downstream showing on the 2019 diagram, looking at it logically.

[muffinmonkey]

Ok no problem I can only find one so presume it is the older version. Would you happen to know if this is the correct part if there is only one?

https://citroendirectparts.co.uk/produc ... de-sensor/

[GiveMeABreak]

Normally we can only supply parts data checks or requests for donating members, as it is chargeable to us, but as you've already supplied the part reference, that is the correct one on the older system.

[muffinmonkey]

Many thanks much appreciated

[SuperSonic72]

About a month ago, I decided to change the NOx sensor myself. Almost always, the thread gets damaged when trying to unscrew it. Removing the old sensor often involves heating it with a torch. If the thread gets stripped, it requires cutting a new one. In my case, it didn't work out, and the new sensor is only partially screwed in - when I tried to screw it in completely it overturns. I've tied it with wire so it doesn't fall out, and it's holding up well for now. Consider renting a car ramp because it's hard to work in that part of the exhaust system while lying under the car. When installing the new sensor, you'll need good diagnostics, like DiagBox, to clear the errors. I bought the new sensor from Aliexpress for 87 pounds. But don't rush to change it, make sure that the old one is indeed faulty. In my opinion, the battery could be the cause. When I changed the sensor, the new one gave me a communication error twice. I've changed my battery as well as the start/stop system stopped working, and after replacing it, everything with UREA system works perfectly. So I think that when starting, if the battery is weak, the sensor might be sensitive at low voltage and fail to communicate.

[wwwalker]

Hi

Did you get this issue sorted? I have same error code and am thinking of replacing Nox sensor.

Also in the last week had error P0428 for Catalyst temperature sensor. I had that replaced but this NOx sensor error has come up now so wondering if could be another issue causing sensor problems in general. Have read a lot about problems with AdBlue system.

Thanks

[davisoliver077]

It sounds like your Relay’s AdBlue and NOx sensor system has gone into fault mode, which is quite common on the 2.0 HDi engines from around that year. The U059E error code means the ECU (engine control unit) is receiving invalid or corrupted data from NOx Sensor A, this sensor sits in the exhaust system and measures nitrogen oxide levels so the AdBlue system can adjust properly.

When the sensor fails or gives bad data, the ECU can’t calculate the correct AdBlue injection rate, so it triggers both the “Check AdBlue” message and the engine light. If left too long, it can eventually put the van into a limited-power mode.

Before replacing the sensor, it’s worth checking a few things:

• Inspect the wiring and plug for corrosion, moisture, or broken wires, this alone can trigger that code.

• Check the AdBlue quality (if the fluid is old or contaminated, it can also confuse the system).

• If everything looks clean and the wiring is good, then replacing the NOx sensor is the logical next step.

There’s a great explanation of this exact fault and what causes it here:

https://xenons4u.co.uk/blog/u059e-u059f ... explained/

That article goes into detail about what the code means, common symptoms, and what you can do before replacing parts. It also notes that sometimes both sensors (upstream and downstream) can fail over time.

I’d strongly avoid an AdBlue delete, as it’s technically illegal for road use and will fail future MOTs or emissions checks. A proper fix (usually a new NOx sensor and clearing the fault codes) will restore normal operation.