Adblue tank repair details

[roslinde]

Hello all,

I am currently experiencing the P20E8 error on my C3 1.6 BlueHDI. Inspired by the findings in this thread, I purchased the pressure sensor from the suggested link. Meanwhile the adblue warning countdown activated and went away automatically a few times. Several times, the adblue warning went away and so did the check-engine light. But it always came back again eventually with the same P20E8 warning.

After receiving the new sensor, I emptied the tank and replaced the sensor. Pretty straightforward, and reasonably easy to do in the driveway. Replaced the ad-blue fluid and added anti-crystalisation liquid as well.

After replacing the sensor, the error initially went away but came back after a short drive on the highway.8500

After reading this thread again, I worry that I purchased the wrong HM8500 sensor, as two different types exists. A 4-7 bar sensor and a 1-13 bar sensor. Initially when looking at the pressure curves provided by the manufacturer, I thought the 1-13 bar sensor would be the best fit. However, in retrospect, I should probably have picked the 4-7 bar sensor as suggested by others in this thread. Perhaps this is why the repair was not successful?

Alternatively, could the NTC issue mentioned in the TSB result in the same P20E8 error? I have just gotten access to a DiagBox and will verify both the pressure and temperatures tomorrow.

Thanks for all the info on this thread. Saved a good few quid. I also now have a spare AdBlue sensor sat on my parts shelf, so if anyone is desperate for one I can chuck it up on eBay. Thanks again chaps! I encourage anyone who may be lurking this thread like I was to give it a go.

I could be interested in purchasing this sensor from you, as the shipping from the manufacturer takes absolute ages, and I would really like to fix this issue before the car has to go through MOT

[DaleG]

Hello roslinde!

The intermittent nature of it is a bit odd. Do you have a code scanner that allows you to read live data? It'll let you get a better idea of what's happening. And did you do a reset/replacement of the tank after replacing the sensor? On my Topdon artidiag 600s I have the option to tell the car it's had a new UREA tank. I did that after the sensor change to re-initialize everything. It might be worth trying that if you haven't?

I'm certainly open to sticking the sensor on eBay though should you want to try the 4-7bar sensor if all else fails.

[Forrester123]

For the last 2 weeks I have had both the emissions & engine warning lights/messages on.
Took it to a main dealer for a diagnosis & they said I need a new ad-blue tank etc. at a cost of £1200.
However, none was available for 2/3 weeks so i went on holiday for a week & on the last day the mileage countdown was 350.
Surprise, surprise, the day after arriving home the emissions light went out followed by the engine management light the next day. So obviously the long fast run did the trick, but will it be permanent? I do mainly local motoring.

[Trickiedickie]

Hello all!

Apologies for bumping, but I just wanted to relay my experience in fixing my AdBlue tank by purchasing the sensor posted earlier by Trickiedickie. https://www.alibaba.com/product-detail/ ... 69608.html

I had the low pressure fault, along with hearing the pump screaming from the rear of the car as soon as my cat got to temp, so based on Stuart's initial post pointing to a likely failed sensor I ordered a couple from that link. One of the reviews stated theirs arrived mechanically damaged, so ordered a spare for some insurance; it cost me I think ~£70 for the two delivered to the UK. The factory appear to have two specifications for that same SKU and I was asked which I wanted in a DM on Alibaba. A 4-7 bar sensor and a 0-13 bar. Based on the diagram posted again by Trickiedickie, and seeing 4bar as the base value in scanner live data, I opted for the 4-7 bar sensor. Took maybe 1 month ish to get here, and it was a dead simple part swap. The screws around the top of the tank were rusty as hell, but I cleaned them out best I could with a sharp pick and just went steady.

Car is working good as new. Soon as the cat hits 175, it pressurizes up to ~6bar peak, settling at around 5.8 bar. Then slowly trickles down while the cat remains at temp to ~5 bar at which point it quickly re-pressurises back to 5.8.

Thanks for all the info on this thread. Saved a good few quid. I also now have a spare AdBlue sensor sat on my parts shelf, so if anyone is desperate for one I can chuck it up on eBay. Thanks again chaps! I encourage anyone who may be lurking this thread like I was to give it a go.

Thanks for coming back and reporting how it went. And well done!
Your choice of using the 4-7 bar sensor over the 0-13 bar version is probably the right choice though I am uncertain how the latter would perform in practice.

[Trickiedickie]

For the last 2 weeks I have had both the emissions & engine warning lights/messages on.
Took it to a main dealer for a diagnosis & they said I need a new ad-blue tank etc. at a cost of £1200.
However, none was available for 2/3 weeks so i went on holiday for a week & on the last day the mileage countdown was 350.
Surprise, surprise, the day after arriving home the emissions light went out followed by the engine management light the next day. So obviously the long fast run did the trick, but will it be permanent? I do mainly local motoring.

My advice would be to drain the adblue tank and dispose of the contents. This is because there is a possibility there are adblue crystals formed and floating about in the tank. If you ever look at old (1 or 2 years old) adblue in its container you will often notice the formed crystals that can easily cause blockages. The crystals can easily form in and block the adblue injector as well and often requires cleaning.
So, drain out and then refill with fresh adblue. Make sure the manufacturing date is recent ie. within 3 months. Also add a 125ml bottle of Wynns crystal clean and protect. Then its fingers crossed and hope it never comes back.

[roslinde]

Hello roslinde!

The intermittent nature of it is a bit odd. Do you have a code scanner that allows you to read live data? It'll let you get a better idea of what's happening. And did you do a reset/replacement of the tank after replacing the sensor? On my Topdon artidiag 600s I have the option to tell the car it's had a new UREA tank. I did that after the sensor change to re-initialize everything. It might be worth trying that if you haven't?

I'm certainly open to sticking the sensor on eBay though should you want to try the 4-7bar sensor if all else fails.

I did connect the Diagbox and monitored the live pressure, but only when the adblue warning was still on. In this case, the pressure was surprisingly low, i.e. 4.111 right after turning on the car. Since the error disappears eventually, I need to repeat the test next time the error is gone. But not sure if it is wise to drive around with the tester plugged in. My tester is a DiagBox, i.e. the "official" way to test these PSA cars.

Over the last week, the error has been consistently disappearing after driving for some time and then coming back on after some time, usually if the car has been parked for a few days. But when the error disappears, it stays away and all the warnings (adblue, check engine) disappear. I think it makes sense, as the analog sensor output at ~6bar does not match the expected value. And since the sensor does not have an offset of 4bar, the pressure at startup will probably also be wrong.

One new thing I noticed was that I had a P20E9 error, which I had never seen before changing the sensor. I guess this could also be explained by the wrong sensor type?

Since changing the sensor, i have not had the 1100km countdown at all.

I did not tell the car that I swapped the UREA tank, perhaps I should do that next time I pull the tank.

I think the next step is to change the sensor to the correct type. I may need to purchase it from you, unless the gets it shipped quickly

By the way, the plastic screws on the top of the tank are very rusty. Did anyone find a matching screw replacement? It would be nice to swap them while I have the tank removed.

[Trickiedickie]

@roslinde
A couple of things...........
I have also seen/had the P20E9 error combined with the P20E8. P20E9 means high pressure which is often caused by crystals forming in the adblue tank etc and forming partial blockages, just as I mentioned in the post above. Also removing and cleaning the adblue injector is a good idea. Draining and refilling with fresh adblue and the additive is important.

With diagbox you must make sure all the error codes are deleted as some are 'temporary' and others are 'permanent'

[Stuart W]

Just a reminder to those of you with suspected adblue tank problems.Do not use the pressure readings from diagbox or any other diagnostic.These readings are derived from the pressure sensor, which is probably faulty, hence the reason for this mod.Fit a pressure gauge(very cheap) to a short piece of pipe directly from the outlet of the adblue tank or at the injector.This will tell you at once if the fitted sensor is the cause of your problem.
A faulty sensor sends faulty readings to diagbox.

[Stan93]

"by DaleG » 12 May 2025, 09:39
Hello all!

Apologies for bumping, but I just wanted to relay my experience in fixing my AdBlue tank by purchasing the sensor posted earlier by Trickiedickie. https://www.alibaba.com/product-detail/ ... 69608.html"


Hi DaleG could you tell me how you got past the 10 piece minimum order thanks.