ECU fault with NOX Sensor cabling

Faults and Technical chat for the Citroen C4 Cactus
spacyzuma
Posts: 9
Joined: Wed Sep 18, 2019 6:08 pm

ECU fault with NOX Sensor cabling

Post by spacyzuma » Tue Oct 27, 2020 11:35 am

I bought my car August 2019. Since then, I’ve taken it to the garage more than 5 times because of repeated issues with the AdBlue/exhaust system.
Recently, the Check Engine light came on again. I used by OBDII reader to check the error codes and the errors are:
U029D – Lost communications with NOX Sensor A
U029E – Lost communications with NOX Sensor B

Also, a distance countdown is now displayed on the dashboard. It’s currently at 600 miles.
I took it to the garage again last week. They checked the NOX Sensors, which are fine. I paid £72 for an electrician to inspect/test the NOX Sensor cabling to the ECU and this was his diagnosis:
“COMMUNICATION FAULT ON THE CAN LIE TO THE NOX SENSOR.
CHECKED NOX SENSOR FOR OPERATION – CHECKED OUT OK.
CHECKED ALL WIRES FROM MULTI-PLUG TO ECU FOR CONTINUITY – ALL CHECKED OUT OK.
CAN LINE SHOWING FLUCTUATING VOLTAGE SUGGESTING THERE IS A FAULT IN THE ENGINE ECU.
CAR WILL NEED TO GO BACK TO THE DEALER FOR THESE REPAIRS.”

I’ve booked an appointment in 2 weeks with the nearest Citroen dealer. It’ll cost £84 just to assess the problem, and I assume a lot more to fix it. The car is 5 years old and out of warranty.
Has anyone ever experienced this particular problem with the ECU?
Silver 2015 Citroen C4 Cactus 1.6L BlueHDi Feel 100

blackcountrycactus
Posts: 171
Joined: Sat Jan 06, 2018 10:40 pm
Location: west midlands

Re: ECU fault with NOX Sensor cabling

Post by blackcountrycactus » Tue Oct 27, 2020 5:13 pm

could be your adblu tank that is the issue ,make sure it as full citroen service history or if not check yours as had the later adblu filler cap fitted (usually as a white vent in the middle).
All black 1.6hdi flair with pano-2016

spacyzuma
Posts: 9
Joined: Wed Sep 18, 2019 6:08 pm

Re: ECU fault with NOX Sensor cabling

Post by spacyzuma » Wed Oct 28, 2020 2:12 pm

blackcountrycactus wrote:
Tue Oct 27, 2020 5:13 pm
could be your adblu tank that is the issue ,make sure it as full citroen service history or if not check yours as had the later adblu filler cap fitted (usually as a white vent in the middle).
It's not the tank, as confirmed by the Garage.

Each time the Adblue/Emissions warning light has come on, I always top up the tank but the alarm remains and I have to take it to the garage.
Silver 2015 Citroen C4 Cactus 1.6L BlueHDi Feel 100

Jayo
Posts: 4
Joined: Wed Oct 28, 2020 6:24 pm

Re: ECU fault with NOX Sensor cabling

Post by Jayo » Wed Oct 28, 2020 6:31 pm

Hi, I've been having the same problem. I had the UREA light on, Service light and engine management light on altogether. Booked it in to Robins & Day and had to pay £84 just for a diagnostic, got a call today saying it was the oxygen sensor in my exhaust and will cost £476 in total.

routemaster1
Posts: 181
Joined: Tue Mar 26, 2019 3:43 pm

Re: ECU fault with NOX Sensor cabling

Post by routemaster1 » Thu Oct 29, 2020 9:36 am

spacyzuma wrote:
Wed Oct 28, 2020 2:12 pm

Each time the Adblue/Emissions warning light has come on, I always top up the tank but the alarm remains and I have to take it to the garage.
For those who may be having similar issues, if the Adblue alarm is on and you attempt to top up, note that you need to put a significant quantity in before the system will reset. This quantity would be a minimum of ~4L. If you add more than 4 litres and the alarm remains on you need to get it sorted. Addition of 4 litres should give a range of ~2,500 miles, so if the alarm goes off and recurs within that kind of distance the problem isn't solved.

spacyzuma
Posts: 9
Joined: Wed Sep 18, 2019 6:08 pm

Re: ECU fault with NOX Sensor cabling

Post by spacyzuma » Thu Oct 29, 2020 2:58 pm

Jayo wrote:
Wed Oct 28, 2020 6:31 pm
Hi, I've been having the same problem. I had the UREA light on, Service light and engine management light on altogether. Booked it in to Robins & Day and had to pay £84 just for a diagnostic, got a call today saying it was the oxygen sensor in my exhaust and will cost £476 in total.
WOW!! £476!! Outrageous!
Silver 2015 Citroen C4 Cactus 1.6L BlueHDi Feel 100

Jayo
Posts: 4
Joined: Wed Oct 28, 2020 6:24 pm

Re: ECU fault with NOX Sensor cabling

Post by Jayo » Thu Oct 29, 2020 7:03 pm

Got the car back today, just a relief to have them stupid lights off. A costly experience but when Ive looked into it, it's common for this to happen between 50000 and 60000 miles, must be down to wear and tear.

routemaster1
Posts: 181
Joined: Tue Mar 26, 2019 3:43 pm

Re: ECU fault with NOX Sensor cabling

Post by routemaster1 » Fri Oct 30, 2020 8:27 am

spacyzuma wrote:
Thu Oct 29, 2020 2:58 pm
Jayo wrote:
Wed Oct 28, 2020 6:31 pm
Hi, I've been having the same problem. I had the UREA light on, Service light and engine management light on altogether. Booked it in to Robins & Day and had to pay £84 just for a diagnostic, got a call today saying it was the oxygen sensor in my exhaust and will cost £476 in total.
WOW!! £476!! Outrageous!
Which is why the Citroen warranty is so valuable. I had a similar sensor go on our petrol C3 and was quoted a similar sum until they realised that it was a 2019 car!

spacyzuma
Posts: 9
Joined: Wed Sep 18, 2019 6:08 pm

Re: ECU fault with NOX Sensor cabling

Post by spacyzuma » Fri Oct 30, 2020 9:50 am

Jayo wrote:
Thu Oct 29, 2020 7:03 pm
Got the car back today, just a relief to have them stupid lights off. A costly experience but when Ive looked into it, it's common for this to happen between 50000 and 60000 miles, must be down to wear and tear.
I see. I bought my car at 61k miles and it's now at 67k.
From your experience, I guess I'll budget about £500 for repairs. Sigh.
Thanks for sharing.
Silver 2015 Citroen C4 Cactus 1.6L BlueHDi Feel 100

spacyzuma
Posts: 9
Joined: Wed Sep 18, 2019 6:08 pm

Re: ECU fault with NOX Sensor cabling

Post by spacyzuma » Thu Nov 12, 2020 12:36 pm

I just got a quote from Robins & Day (Glasgow).
I'm being charged £252 for 2 sets of diagnostic tests, and a total of £1483 to fix the car. They say the problem is the Urea Reservoir which needs to be replaced.

At this rate, I'm thinking of selling the car. I'm tired of all this.
Silver 2015 Citroen C4 Cactus 1.6L BlueHDi Feel 100

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