Diesel Emmission Fluid

my wife drives a LR Discovery diesel. This is the SDV6 engine. Periodically when she is driving the light comes on saying “DEF” or diesel emmission fluid is low or soon will be low. It goes away after a little while, or at least it did the last time I was in car (my wife and kids live in foreign country so i don’t see the car often

In the past she’s told me she just adds more fluid to the reservoir and it goes away. I’ve never owned a diesel car before but it strikes me as strange that it would just burn off. Is that normal for a top-off to be required or is it indicative of a leak of some kind? She plans to sell the car when she moves back to the states (it is RHD) so we’re not keen on fixing something that requires major maintenance.

As an aside, LR makes really nice diesel trucks. I mean it is really quiet and doesn’t have that diesel funk.

DEF is used to reduce emissions from diesel engines. It is injected into the engine and is burned off.


Yup, a friend of mine bought a top of the line GMC 4X4 diesel, she learned about the DEF when the light came on.

That fluid is consumed–in very small quantities–along with the diesel fuel, in order to reduce emissions.

It sounds like your wife knows much more about modern diesel vehicles than you do.


Yes, they do. Very quiet, and powerful.

But they are not to be owned past the warranty period as they become VERY unreliable and VERY expensive to repair as they age. That is why they become very cheap to buy as used cars here in the US. Although, right now, even used LR’s are pretty expensive!


… which is the result of using that urea-based emissions fluid. Every modern diesel auto maker uses this technology, which I believe was pioneered by Mercedes.

A neighbor bought one several years back, and the local joke was “what color is Tony’s Rover THIS week”. That bomb was in the shop several times each month, and he wound-up driving a loaner Rover almost as often as he drove his own Rover. Finally, he had the sense to dump it, shortly after the warranty expired.

Personally, I think that is about to change in the used car market writ large heading in to 2022 early 23. There has already been slight price declines and some of the I-bank research is hinting at large amounts of loans for used ccars that are highly likely to head in tonegative equity status. So, a lot of people are going to be stuck with a used car they over paid for in the last two years and used stock will be hard to turn over at current prices. And as the new market comes fully back online one would expect dips in price point for both new and used. If I had a second car right now, I’d probably sell my Mustang for a little over 30k, wait 12 months and buy another. (Never should have sold my MB 4 years ago).

Thanks for the feedback. I didn’t know DEF was supposed to burn off, I assumed it was like coolant or something.

your Landrover’s owners manual will explain all about DEF and the proper useage of it. I highly suggest you read it. It will also detail the Government enforced issues that will arise if you run out of DEF…

As you have already learned the exhaust fluid is injected into the exhaust to help the particulate filter clean up the sooty exhaust it collects. So it’s a use item much like washer fluid or gasoline. How often it needs to be filled depends on how much and how far she drives, and under what conditions.

You can buy DEF in small or large quantities and keep it in the garage at home, or buy what you need at diesel fueling stations. I recommend just buying what you need when you need it, from a place that does brisk business. DEF has a shelf life and goes bad over time, I wouldn’t use any that’s a year old.

The OP is finally admiting there is something he didn’t know will wonders never cease.