AdBlue/DEF Range Thread

Engine, Exhaust, Drivetrain, ECU Faults and Fixes
sddawson
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Re: AdBlue/DEF Range Thread

Post by sddawson » Sun Jul 02, 2017 1:48 pm

Ok, but at least to where you could see the liquid near the top? I just don't understand how even filling it to the point of spilling out could ruin a sensor that required the whole tank to be removed. Where is this sensor?
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Mamil
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Re: AdBlue/DEF Range Thread

Post by Mamil » Sun Jul 02, 2017 2:34 pm

sddawson wrote:
Sun Jul 02, 2017 1:48 pm
Ok, but at least to where you could see the liquid near the top? I just don't understand how even filling it to the point of spilling out could ruin a sensor that required the whole tank to be removed. Where is this sensor?

From what I've read in the workshop manual, it seems the AdBlue level sensor works on ultrasonic principles, ie. it bounces sound waves off the surface of the AdBlue in the tank to calculate it's level. For this to work there needs to be a permanent air gap at the top of the AdBlue tank itself, as the sound waves only reflect off a fluid/air barrier. Therefore, if you overfill the tank and this air gap is eliminated then the level sensor won't work and the DEF system goes into an error state. The sensor module is "located at the bottom of the DEF tank, and is welded into the tank and can only be replaced as a complete assembly". So, if the tank is overfilled it's entirely possible that to clear the fault you need to drain the tank and refill, then reset the sensor, for which 205 quid would be a reasonable charge at main dealer rates.

However, that's all just speculation on my part from reading the manual and what Green Genie said the dealer said to him :D
Last edited by Mamil on Sun Jul 02, 2017 2:45 pm, edited 1 time in total.
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Re: AdBlue/DEF Range Thread

Post by Chippy » Sun Jul 02, 2017 2:45 pm

Mamil wrote:
Sun Jul 02, 2017 2:34 pm
sddawson wrote:
Sun Jul 02, 2017 1:48 pm
Ok, but at least to where you could see the liquid near the top? I just don't understand how even filling it to the point of spilling out could ruin a sensor that required the whole tank to be removed. Where is this sensor?

From what I've read in the workshop manual, it seems the AdBlue level sensor works on ultrasonic principles, ie. it bounces sound waves off the surface of the AdBlue in the tank to calculate it's level. For this to work there needs to be a permanent air gap at the top of the tank, as the sound waves only reflect off a fluid/air barrier. Therefore, if you overfill the tank and this air gap is eliminated then the level sensor won't work and the DEF system goes into an error state. The sensor module is "located at the bottom of the DEF tank, and is welded into the tank and can only be replaced as a complete assembly". So, if the tank is overfilled it's entirely possible that to restore the air gap and clear the error you need to dismantle the tank and replace the whole sensor module.

However, that's all just speculation on my part from reading the manual and what you described the dealer said to you :D
Interesting - in that case I should have an error warning which I don't. Surely the air gap would be restored when the fluid level drops due to usage.

There should also be a visible warning somewhere to tell you under no circumstances to overfill.

Now we've gone full circle - how do we know when it's full or overfilled. In the handbook it refers to a full system refill. Whatever that is supposed to mean is anybody's guess.
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Re: AdBlue/DEF Range Thread

Post by Mamil » Sun Jul 02, 2017 2:54 pm

Chippy wrote:
Sun Jul 02, 2017 2:45 pm

Interesting - in that case I should have an error warning which I don't. Surely the air gap would be restored when the fluid level drops due to usage.

There should also be a visible warning somewhere to tell you under no circumstances to overfill.

Now we've gone full circle - how do we know when it's full or overfilled. In the handbook it refers to a full system refill. Whatever that is supposed to mean is anybody's guess.
I'm afraid I can't answer that Chippy, as I'm just joining the dots from what it says in the manual and what other's have reported their dealer's have said. If I was to guess I'd say the filler tube doesn't enter the tank right at the top so that some air is always trapped at the top of the tank to provide the required air gap for the sensor to work. So, you can fill the fill tube up to the brim without eliminating the air gap in the tank. However, in some circumstances, such as forcing Adblue in under pressure, if the car is on a slant, or if you agitate the tank (by driving for example) then top it up again you may be able to overcome this 'gravity' system and eliminate the air gap, in which case you'd get the error message. But as I say, that's all just speculation on my part based on a little knowledge and a lot of guesswork :D

I do agree that it would seem to be a stupid design that allows owners doing simple top-ups to somehow "overfill" the system that then requires an expensive trip to the dealer to fix it, and hopefully as Green Genie suggested a few posts ago, there is some re-design in the works from Land Rover to prevent this happening in the future.
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Re: AdBlue/DEF Range Thread

Post by Chippy » Sun Jul 02, 2017 3:20 pm

I've just been reading up on how ultra sonic fluid level sensors work since I had absolutely no idea.

For anyone interested here is a link to a Texas Instruments site where the function is described on page 5.

http://www.ti.com/lit/an/snaa220a/snaa220a.pdf
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Re: AdBlue/DEF Range Thread

Post by Mamil » Sun Jul 02, 2017 3:38 pm

And here's the relevant bit from the service manual which talks about the need for an air gap in the tank so the ultrasonic sensor will work, and how overfilling can eliminate this and cause an error state...
The DEF tank is fitted with combined temperature/ultrasonic level sensors. Circuit continuity and plausibility of the signals
received are checked within the ECM. An ultrasonic “no echo malfunction” is set if no valid echo from the ultrasonic sensor is
detected during a predefined time. This typically happens when the ultrasonic signal of the sensor is blocked, or if the DEF
tank is overfilled (the air pocket at the top of the DEF tank is no longer present).
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Re: AdBlue/DEF Range Thread

Post by Chippy » Sun Jul 02, 2017 3:42 pm

Mamil wrote:
Sun Jul 02, 2017 3:38 pm
And here's the relevant bit from the service manual which talks about the need for an air gap in the tank so the ultrasonic sensor will work, and how overfilling can eliminate this and cause an error state...
The DEF tank is fitted with combined temperature/ultrasonic level sensors. Circuit continuity and plausibility of the signals
received are checked within the ECM. An ultrasonic “no echo malfunction” is set if no valid echo from the ultrasonic sensor is
detected during a predefined time. This typically happens when the ultrasonic signal of the sensor is blocked, or if the DEF
tank is overfilled (the air pocket at the top of the DEF tank is no longer present).
Sorry Mamil I didn't read all of the section in the manual but you're right and I'm baffled ;)
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Re: AdBlue/DEF Range Thread

Post by Mamil » Sun Jul 02, 2017 3:56 pm

Chippy wrote:
Sun Jul 02, 2017 3:42 pm

Sorry Mamil I didn't read all of the section in the manual but you're right and I'm baffled ;)

No worries Chippy. TBH we shouldn't need to understand all this if LandRover would just design the AdBlue system so it's idiot proof :lol:

To me the whole thing just doesn't seem to have been thought through properly - filler cap in engine bay instead of somewhere easily accessible, reduced fuel tank capacity, ability to overfill it, and wildly optimistic usage rates! Was adding AdBlue to the DS perhaps an afterthought due to the fallout of the VW Dieselgate scandal?
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Re: AdBlue/DEF Range Thread

Post by BFGDSMan » Sun Jul 02, 2017 3:59 pm

Adblue would always have been in the plan for the Ignenium as it was the only way to meet Euro6. I suspect what was not planned for is the amount of adblue to be used, which i think had been "adapted" post VW.
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Re: AdBlue/DEF Range Thread

Post by Chippy » Sun Jul 02, 2017 4:02 pm

BFGDSMan wrote:
Sun Jul 02, 2017 3:59 pm
Adblue would always have been in the plan for the Ignenium as it was the only way to meet Euro6. I suspect what was not planned for is the amount of adblue to be used, which i think had been "adapted" post VW.
I agree estimates with the use of word adapted.
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