Recurring Ad Blue issue - Multiple error codes -control module, pressure sensor, pump

[Mondy]

Hi everyone,

I've searched the forums for the following below codes but there are a few that return nil response.

I'd be very grateful for any guidance or advice related to the below codes and issues.

A quick bit of background; I purchased the car end of Dec, EML light came on 24th Dec, then Ad Blue warning count down shortly after. Car is under a 12 month warranty. I do 20-25k miles a year, and my daily commute is a 75 mile motorway return journey, driven at 70mph+ for 90% of the drive.

Garage (not the dealer garage I bought the car from) took the first EML error code which was related to Nox sensor below threshold efficiency and cleared the codes. Over the next couple of weeks, the EML light and Ad blue warning came on again, but the Ad Blue countdown eventually cleared. The EML light also cleared itself eventually.

Since I bought the car I've covered 2.2 k miles. I made sure the Ad Blue tank was full. I noticed that the level (from the 8' dash display) did not go down once during this time and remained at full which to me, seems to suggest a faulty level sensor or its not being injected into the exhaust.

It was booked in for a NOx sensor replacement (the downstream one I think) which was completed 12th Feb. It was a genuine Nox sensor from Vauxhall. Garage also got other another error code post sensor replacement, related to the DPF (unsure exactly what, I think threshold or pressure), they used some DPF cleaner and ran a regen which was successful and seemed to clean out the DPF. They test drove the car at motorway speeds, slow speeds - all fine with no recurring fault codes. They check the Ad Blue system, no crystallisation on the injector nozzle, all wires seemed intact and plugged into the correct modules. They also emptied some of the tank to a lower level and check for crystallisation and there was none. The Ad Blue tank level then showed the correct level (1/3 of a tank), so the sensor seemed to be working. Ad Blue was topped up just under half.

I picked the car up and that evening the EML light came on a few hours later. A few days later the Ad blue countdown started again. It's now at Engine restart not possible in 210 miles. Also, the 'Service Vehicle Soon' message will appear sporadically.

I took the car to them yesterday to download the stored error codes, shown below:

P10C9 - Reductant control module sensor reference voltage 2 low voltage
P204B - Reductant pressure sensor performance
P208C - Reductant pump control circuit low voltage
????? - Reductant control module lost communication with reductant pressure sensor
P2AD7 - Reductant pump motor position sensor performance
P2BAD - Exhaust Nox concentration high, unknown reason
U2629 - Reductant control module lost communication with reductant tank temperature sensor 1


Prior to this, I've noticed the car was doing regens when I'd driven on short journeys and I allowed them to complete. Oil doesn't smell of diesel (it doesn't have a sweet oily diesel smell), it's within the level on the dipstick, towards the top. Last oil change was end of August. I haven't noticed it do a regen since being at the garage on 13th Feb, but I have mainly been driving on the motorway and it was cleaned out so may be at low saturation.


The garage are going to order a replacement tank, which should come with all the related paraphernalia (pump, sensors etc) as they seem to think the fault is with the pump not actually pumping the ad blue, resulting in the errors and the reason the Nox concentration is high.

I've been doing some reading on the forums and form what I can gather, it will be worth while checking the following;

Glow plugs (using multimeter)
Battery health
MAP & MAF sensor (Where are these located on my engine? I've attached some photos below of the engine bay)
Intercooler/Boost pipe for correct seal at ends and ensuring no cracks/splits
Throttle body / EGR Valve
Another check of the wiring, plugs, contacts and fuses of the Ad Blue system (using contact cleaner if required)




The car is lovely to drive, but it's such a shame that since buying it, I've been trying to rectify another careless owner's problems! I'm looking forward to getting this sorted and hopefully enjoy the car properly.

Thanks for your time and really hoping some expert advice can narrow this down so it's sorted once and for all.

[Drew]

Your map sensor is just at the back of the engine cover, roughly central and on top of the plastic intlet manifold. It's held in with a single bolt and just pulls up and out once you have undone the bolt theres a rubber ring seal. I cleaned mine with carb cleaner don't poke it too much, it looks like a little deflated balloon in a plastic cage.
The maf sits between your airfilter box and the turbo, you'll see the electrical connection. So long as there's been an airfilter in the box it should be pretty clean, it's delicate mind.

[lizzard-t]

If this is under any type of extended warranty then I would leave it in the hands of those who have diagnosed the possible problems.
but for you information only
P2BAD is related to excess nox concentration in the downstream sensor which would lead to insufficient DEF being supplied via the DEF injector .
P2629 jeans you have lost communication to heater control number 1 via the DEF control module
P208c is DEF PUmp control circuit low which would probably explain the increase in NOX concentration.
but
P204B is the most interesting one because it's lost the 5v reference circuit to the pressure sensor the sensor has a resistor inside which variate the voltage being sent back to the DEF ecm ,if the reference circuit is lost it cannot differentiate the pressure,so it has no idea of the pressure probably why the above issue are present.

[Mondy]

Hi all - an update.

The Ad Blue tank has been replaced under warranty (a genuine VX part (GM) which contains all level sensors, pump, control modules etc.

The tank has had 10 litres of ad blue put in, the level sensor works correctly.

The garage have said that the Ad Blue tank control module needed some remote coding (to communicate with the ECM?)

All fault codes have disappeared from the scanner and after a test drive do not come back.

HOWEVER - the no engine start in xx miles countdown will not remove itself.

I spoke to a VX main dealer who said that there were no outstanding recalls for my vehicle and all have been completed, but after reading various stories online, i'm wondering if its a main dealer ECU reset/update?

Would appreciate any advice or things to check prior to taking it to main dealer if the garage cannot resolve.

(P.S Thanks Drew for pointing out the MAF and MAP sensor - i'll get onto those when I have the car back to check them!)

Many thanks all.

[lizzard-t]

You need to,take that back ,that's not been solved ,if it's still displaying no re-start after xxxxxxx miles then the fault is still present.
from what you are saying,it sounds like a independent garbage carried out the installation of the tank ! Is that right ?
if so they need to take it to a main dealer .at there cost ,not yours .

[Mondy]

No start Countdown was cleared, no EML and no fault codes present. Picked the car up tonight.

yes it was an independent garage, they’ve been really good actually. They’ve done all the works so far.

I think the replacement tank needed some coding so the relevant ECM’s could talk to each other. I don’t think it’s a case of plug and play.

the Nox sensor was also replaced under warranty a few weeks prior but I wonder if it’s been the tank and pump all along. I just hope that the Ad blue warning lights, EML and fault codes stay away for a long long long time and fingers crossed I can now enjoy some trouble free motoring!

I really do like the car, but she’s been treating me mean to keep me keen!

[Drew]

Good news and thanks for the update. Fingers crossed that's the end of it.

[Mondy]

Two days later (6th March)... EML Light back on with Ad Blue fault and No engine restart.

I had it booked into Vauxhall main dealer the next day, see if they could work some magic.

EML codes were P20EE and P2BAD for NOx issues.

They checked for the correct injector number (from Technical Service Bulletin 18-e-3403) which it had.

Checked Ad Blue Pressure and tested system - all ok.

Apparently all that was required was a 'Service Bay System test'.

All readings from the test were correct and it completed successfully, reset the ad blue faults correctly. I paid £120 for the privilege!

Looks like it needed some dealer level electronic trickery to give the car it's required test and reset, This is supposedly what the remote coding company were trying to do, but might not have been enough!



Here we are on the 12th - no EML and no Ad blue issues after a few hundred miles of driving.

Let's hope it stays that way...

[Howy]

Glad it's sorted