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Discussion Starter · #1 ·
Our 2008 1.6 HDi (2017 model year) has an engine warning light on and a display warning saying that there's an engine fault and the car needs repair. My cheapo scanner is reporting an error code of U029d which googles as a generic OBD code indicating that the system has lost communication with the NOx sensor. Has anyone had this fault before and is it likely to be the actual sensor or just something as simple as the Adblue needing to be topped up?
 

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i would assume a sensor or wiring fault... you need to get under the vehicle safely and check the wiring.. may have chaffed through on something or been eaten by rodents...stranger things have happened
 

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Discussion Starter · #3 ·
Thanks for the reply. It was due a service in the next couple of weeks so I had it done today and asked them to have a look. Its not a clearcut issue as the warning light has since gone out again but they're going to order in a new NOx sensor and take it all apart next week to see what's going on. Luckily its under warranty so there's no charge.
 

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Discussion Starter · #5 ·
My experience was that the NOx sensor had to be replaced. I've no idea how difficult a job it is but it took the dealer less than two hours to replace. I've no idea of costs either as the car is still under warranty (5 years here in Ireland).
 

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Hi! I had a U029E 87 (DeNOx system ECU) Characterisation of the fault as 'component detected not communicating on the emission control network' - PSA code reading on diagbox.

I was also told by my service centre that it was my Nox sensor and I googled it as Nox Sensor B but U029E was a generic code so you would need Diagbox to be specific with the codes.

Eventually, I found out that the adblue relay was stuck open so it didn't send power to communicate on the canbus system.

I took out the circuit board for the adblue and covered all the plastic connectors and capacitors with aluminium foil. I put it in an air fryer (you can use an electric oven too). I initially started at 100 Celcius and increased the temperature to 180 Celcius over a 3 minute timeframe. You may also preheat to 180 degrees celcius and put the adblue ecu in for 1 minute and see if it work.

I actually heard a pop during the last minute but didn't have much to lose so connected it to the pump and to the car. Amazingly, diagbox didn't read U029E 87 code anymore and the ECU was communicating on the network. I believe the moisture and loss of current in the adblue ECU is causing the relay to arc and malfunction.

Your result may not be the same as mine if you have a bad connection elsewhere but it's worth a try.

I have also sorted P20e8 Urea Fluid pressure too low without resorting to replace pump module or tank. Anyone needs a hand can message me for a workaround that could work for them. I can guide you through the process if you're familiar with the adblue system and have some experience with diagnostics software.
 

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Hi! I had a U029E 87 (DeNOx system ECU) Characterisation of the fault as 'component detected not communicating on the emission control network' - PSA code reading on diagbox.

I was also told by my service centre that it was my Nox sensor and I googled it as Nox Sensor B but U029E was a generic code so you would need Diagbox to be specific with the codes.

Eventually, I found out that the adblue relay was stuck open so it didn't send power to communicate on the canbus system.

I took out the circuit board for the adblue and covered all the plastic connectors and capacitors with aluminium foil. I put it in an air fryer (you can use an electric oven too). I initially started at 100 Celcius and increased the temperature to 180 Celcius over a 3 minute timeframe. You may also preheat to 180 degrees celcius and put the adblue ecu in for 1 minute and see if it work.

I actually heard a pop during the last minute but didn't have much to lose so connected it to the pump and to the car. Amazingly, diagbox didn't read U029E 87 code anymore and the ECU was communicating on the network. I believe the moisture and loss of current in the adblue ECU is causing the relay to arc and malfunction.

Your result may not be the same as mine if you have a bad connection elsewhere but it's worth a try.

I have also sorted P20e8 Urea Fluid pressure too low without resorting to replace pump module or tank. Anyone needs a hand can message me for a workaround that could work for them. I can guide you through the process if you're familiar with the adblue system and have some experience with diagnostics software.

Hi, I hope you maybe able to help me, I have a peugeot 3008 2017, which has fault code U029E - message warning on dash 700 miles until engine wont start. ad blue light on also EML. After fa
Hi! I had a U029E 87 (DeNOx system ECU) Characterisation of the fault as 'component detected not communicating on the emission control network' - PSA code reading on diagbox.

I was also told by my service centre that it was my Nox sensor and I googled it as Nox Sensor B but U029E was a generic code so you would need Diagbox to be specific with the codes.

Eventually, I found out that the adblue relay was stuck open so it didn't send power to communicate on the canbus system.

I took out the circuit board for the adblue and covered all the plastic connectors and capacitors with aluminium foil. I put it in an air fryer (you can use an electric oven too). I initially started at 100 Celcius and increased the temperature to 180 Celcius over a 3 minute timeframe. You may also preheat to 180 degrees celcius and put the adblue ecu in for 1 minute and see if it work.

I actually heard a pop during the last minute but didn't have much to lose so connected it to the pump and to the car. Amazingly, diagbox didn't read U029E 87 code anymore and the ECU was communicating on the network. I believe the moisture and loss of current in the adblue ECU is causing the relay to arc and malfunction.

Your result may not be the same as mine if you have a bad connection elsewhere but it's worth a try.

I have also sorted P20e8 Urea Fluid pressure too low without resorting to replace pump module or tank. Anyone needs a hand can message me for a workaround that could work for them. I can guide you through the process if you're familiar with the adblue system and have some experience with diagnostics software.

Hi, I hope you maybe able to help me, I have a peugeot 3008 2017, which has fault code U029E - message warning on dash 700 miles until engine wont start. ad blue light on also EML. After fault code reading it came up no communication with denox. I have taken the ad blue tank out and seperated the pump and the well it sits in was full with ad blue liquid (is this normal?) considering electrics?. any help would be much appreciated.

Thanks
Paul.
 

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The area where the pump module and ECU are located shouldn't be having any urea. It's a sealed dry area. You might have had a leaking seal or the pipe from the tank to the motor might have a leak. In any case, you could try cleaning the ecu with contact cleaner and leaving it out to dry properly and try see if that enables the pump to work again monitoring for any leak. If you have everything opened, you should hear the relay on the adblue ecu 'click' to turn on the power supply. The U029e code would mean there is no power supply to the adblue ECU. If that's the case where the relay doesn't turn on, these boards have a fault with the soldering of the microprocessor (MCU) that runs the firmware. You can try using a heat gun to re-solder the many legs of the MCU on all four sides though it's usually the side where the big capacitors are they fail causing the MCU not to reset itself.
 

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I took out just the ECU and would connect the wire harness with the ignition on to see if the relay works. If that power is going through, you need to assemble everything back. If the power cuts off, you might get the U029e code along with P20e8 etc. In which case, you need to re-solder the MCU because the failure is the legs having a dry/cold joint that doesn't provide for a good connection. Hope this helps.
 

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Hi!
...
I have also sorted P20e8 Urea Fluid pressure too low without resorting to replace pump module or tank. Anyone needs a hand can message me for a workaround that could work for them. I can guide you through the process if you're familiar with the adblue system and have some experience with diagnostics software.
I just got the same P20E8 00 fault on my 2016 Partner 1.6BlueHDi 100 (BHY).

I can hear the AdBlue pump work, however it stays at 4Bar all the time and cannot run the Denox system test from ACTUATOR TEST in DiagBOX.

I would be very grateful if you shared some info on how exactly you fixed this error.

I do not have the U029E fault.

There is more than 6L of AdBlue in the tank.

The NOx reading shows max 270PPM at full throttle and full engine load with the error displayed.
 

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If you've taken the injector and pump module out, try the denox flow test. If it doesn't work, try plug off the adblue harness to the adblue ecu while the ignition is on to see if the relay is clicking. Then report back.
P20e8 means the pump is getting cut off but the relay is supplying power to the ecu and needs to be reset using diagbox by either clearing the fault codes or by re-initialising the denox system. It could also mean, you have an airlock. When I do the denox flow test and the motor runs after the system is opened up and put back, I blow into the filler hole to force the urea into the pump.
 

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You also need to check if it says injection authorised in denox parameter 2

Including this for reference only. This data for U029e where the relay doesn't power on the primary circuit at all hence the pumps can't work.
Wood Mesh Font Rectangle Composite material
Mesh Wood Font Pattern Pet supply
 

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The injection based on temp is authorised, but the injection based on pressure is not.

The bleed status changes from waiting to 1, then to 2 and then the error P20E8 00 comes on with the UREA lamp on the dashboard. The pressure is displayed as 4Bar constantly, no change there.

I have not yet taken the AdBlue tank or injector off of the car, but I will in the days to follow.

It seems to me the injector could be leaking as the NOx PPM never goes over 270ppm even with the error.

What is the PPM value with the system not injecting AdBlue into the exhaust?
 

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If you can't do the denox flow test, there could be a canbus fault due to damaged components in the adblue ecu or a bad joint somewhere. This is a bit tricky to fix because sometimes I've had the ecu come back alive after heating some areas with a hot solder. The first time, I stuck it in an air fryer and let it cook for 3 mins at 200C and it came back to life after being dead for 2 years. Then I started changing random components on another board and got that to work. So if nothing looks damaged it could be a bad pcb board or joint.
 

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Okay, so.

I drained the whole AdBlue tank today -thank God they`ve left a drain plug on the bottom.

16L came out, which is clearly way more than it is supposed to have in there.

I did the connector disconnect while the car is running, the relay clicks loud and clear.

I then filled 8L back in the tank.

Reset the AdBlue system via the REPAIR menu in DiagBOX and cleared all the faults.

I also tested if any air was going through the blue cap on the filler neck - no bueno, neither by sucking, nor by blowing in it was I able to get any result. So, naturally, I took of the small white cap of the valve, cut the filter membrane and put the white cap back on - this time air was going through it. I also put a small piece of sponge on the back, so that no contaminants make their way into the AdBlue.

Went for a drive ET VOILA - no more drama. The pressure is stable at 5.3Bar and the AdBlue injection works.

I did about 120km today, I`m doing another 400km on Friday - we`ll see how it goes.
 

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I tink the adblue tank does take 16 or so litres. I've certainly aded 10 litres to mine when nearly empty and it hasn't overflowed. I never let it go down to the warning light level.
 

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It's a 17l tank.. mine anyway for 2.0 bluehdi. There are others which look smaller maybe 10l. The 17l adblue tank should give 12500km range to about 20k km range.

Great it's working for you Dino. The white filter membrane in the cap only allows gas to flow through. I had one owner drill holes in the cap but the urea sloshed everywhere and stuck to the rear undercarriage forming crystals and I don't think that's kind to the galvanised body.
Adblue cap seal
 

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I can just assume mine was blocked anyway, no matter how high-tech this membrane is supposed to be.

I wash the car every week (plus engine bay and undercarriage) so I am not really worried about any spills or corrosion.

I will observe whether any evaporation leads to crystallisation/spills around the filling neck or chassis and I will report back.
 

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There are too many emissions fault/ urea fault threads to help the owners facing this issue so I'm going to share what I know and what I did to fix the problems for 4 cars so far.

1. Diagnose the fault codes using Diagbox
2. If it shows P20e8/P20e9 or U029e etc related to the adblue system, urea tank or denox system go to the next step (sometimes you may get codes for the nox sensor as well as other codes when you scan the Engine ECU
3. If it's under warranty 5 years or 150k km, Peugeot/Citroen should give you a replacement tank (I've had my own tank fail twice 2 years apart at 30k km and 55k km and the PSA dealer in Malaysia washed their hands clean despite being within the recall period PSA is giving in other countries)
4. If they don't want to replace, you're on your own and you need to either find someone to disable the urea/adblue system or find the fault and fix it yourself or a trustworthy mechanic.
5. If you have Diagbox and know how to proceed dismantling the urea tank and the injector for testing purposes, please proceed.
6. Inspect for leaks from inside the pump module to the injector.
7. If there is a leak, you have to replace whatever is faulty - hose from the tank to the pump, the pump itself, the hose from the pump to the injector or the injector.
8. If you get P20e8 (urea pressure low) P20e9 (urea pressure high) and there are no leaks or blocks, chances are it's ECU related. Same goes for U029e which is definitely adblue ECU related.
9. Your options are to get a second hand ECU alone or the pump module with ECU inside. The problem is many pumps, ECUs and tanks are likely faulty like in my case when I bought a pump module with ECU on eBay but it's a risk you take.
10. My eBay ECU worked temporarily and popped the codes mentioned in this post after a 6km drive and the pump was found to be leaking.
11. You can get the seals and o-rings to fix the pump except for the rubber on the accumulator which is the black cylindrical thing. It might have some cracks on it in which case you need a better pump assembly or maybe fix it somehow by using a strong flexible sealant. It has to handle 6bar pressure.
12. To test the adblue ECU, I turn on the ignition with only the adblue ECU and plug in the harness to the ECU (make sure you connect it correctly after removing the board from the pump casing as the connector tab has to be facing the smooth green side and not where the components are located). The relay should click a few times. If it does and you get P20e8 etc with no leaks or blockages, your power to the ECU is cutting off due to a canbus fault or the urea level sender/temperature sensor giving incorrect readings.
13. Check the urea level on Standard Parameters Measurement for Denox 1. If you have enough urea, it should show the level being greater than 6litres.
14. If the reading is 0 or erratic, you need to change you tank because the sensors are inside. You can also trick the ECU by cutting the black wire from the tank with the black connector which has Black, Red and White wires. The White wire is the Signal and you should get a reading of 4V to 5V to get the adblue ECU to think you have more than 6litres of urea.
15. If the temperature sensor is showing 0, that is an invalid value so you have a problem with the 2 temperature sensors inside the tank. There are 2 pairs of Blue and Yellow wires coming out of the tank and I cut one pair and joined one back to check the temperature on Standard Parameters Measurement for Denox 2. Find out if the temperature reading is what it should be. For me, it was around 30C which seems about right for a tropical climate.
16. If all the readings are correct, and you still have the P20e8 etc, the board is faulty as stated above due to the conformal coating trapping moisture or faulty components. I did fix the boards but it takes a lot of time and some soldering skill and knowledge of reading SMD codes to order the correct components.
17. If you plug the adblue ECU board to the harness (make sure you connect it correctly after removing the board from the pump casing as the connector tab has to be on the smooth green side and not where the components are located) and the relay does not click, the error code will be U029e where the main ECU does not communicate with the denox/adblue ECU. If you use a generic OBD code reader, it might show as a faulty NOX sensor but it's not so use Diagbox otherwise you might be wasting money on changing the NOX sensor like me.
18. U029e fault is with the adblue ECU due to the conformal coating, bad solder joints or components. I fixed this too but it may vary from board to board.

Hope this helps anyone with the troubleshooting. Cheers!
 
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