# DEF Light and Engine Light come on



## Chunk (Aug 31, 2021)

After I run tractor for 5 to 10 minutes my Mahindra MForce 105s 2017 tractor DEF light and Engine Light come on. DEF tank has def!
I just purchased tractor do not have manual to tractor. Any suggestions on what is going on?


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## BigT (Sep 15, 2014)

Good Morning, Chunk. Welcome to the forum.

I found the following explanation regarding DEF on the internet:

"DEF is sprayed into the *exhaust stream of diesel vehicles to break down dangerous NOx emissions into harmless nitrogen and water*. This system is called Selective Catalytic Reduction (SCR) and can be found on 2010 and later model year"

So, I gather your tractor engine is spraying DEF into the exhaust stream when the DEF light comes on. Can you give us an idea of how much DEF your tractor uses (per hour)?? And cost of DEF??


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## pogobill (Jan 31, 2012)

I think you may have to run it so that you get up to a higher operating temperature to burn off the soot in the in the regen filter. 
The light you speak of may be the tractor trying to go into it's regen mode.


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## SidecarFlip (Mar 25, 2021)

BigT said:


> Good Morning, Chunk. Welcome to the forum.
> 
> I found the following explanation regarding DEF on the internet:
> 
> ...


It's a bit more complex than that. T4 final diesels have a power break (flywheel horsepower) where they can be non emissions and still be sold. I believe any new unit under 25 horsepower don't require any emissions hardware presently (but that is changing as well). Over 25 horsepower requires (by Federal Law) a passive catalytic reduction cannister (which is the large cylindrical can the exhaust enters. Inside, there is a honeycomb insert coated with a noble metal that reacts with the soot the engine makes (visible particulates, smoke) and when the engine goes into 'Regen' which is ECM controlled, the soot is burned off and reduced to ash, which drops into the bottom of the cannister and at some point, the cannister element has to be cleaned or replaced (Kubota, which is what I'm familiar with) calls out 2500 regen's before cleaning or replacement.

DEF (which is nothing more than deionized water and urea) is injected into the exhaust stream to catalyze and reduce stack emissions and works in conjunction with the SCR cannister, all monitored by the on board ECM and why emissions compliant engines are all now common rail high pressure injection, versus the old style mechanical injection pump.

The system is very complex to say the least and trouble prone as well. Liquid DEF freezes at 32 (f) so not only does the system have to have the DEF injection hardware, if you use the engine below freezing temps, the DEF system requires the fluid to be heated so it will flow.

Don't know the power break where Federal Law requires DEF and SCR but I do know that all larger units (100 pto and up?) require both.

DEF is relatively inexpensive and you can purchase it in gallon jugs or 5 gallon pails about anywhere, even Wally World has it.

One thing that is intrinsic to not only DEF reduction but SCR reduction is heat'. Both methods require the temperature in the cannister to be elevated for the reaction to take place, hence the higher rpm during 'regen'.

Why I have and use pre Tier 4 final units and will never buy a post 4 unit and why post 4 units (no emissions hardware) are increasing in value and getting harder to buy used everyday. As emissions systems become more complex, so does the incidents of breakdown increase and...

Unlike mechanical injected pre 4 engines, you cannot just throw parts at them. The ONLY way to diagnose an issue (other than a mechanical related issue like a failed head gasket or faulty water pump) is to plug into the ECM and download the trouble codes and then replace the failed parts, which is what the 'Right to repair' with JD tractors is all about and that applies to other makes as well because accessing the ECM (unlike the automotive related OBD connector where you can go buy a scan tool and access the electronic 'brain' don't exist. Each manufacturer has it's own unique data access ports that require the use of the manufacturer's software / scan tool.

In Kubota's case, it's called a 'Diagmaster' scan tool and you cannot buy one. Only an authorized dealer has it and even they don't own it. The dealer 'leases' it from Kubota and pays them for the use of it and there are constant electronic upgrades to the tool as parameters change and system upgrades take place.

I kind of skimmed the surface of how a T4 final unit operates and why I won't have one.


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## SidecarFlip (Mar 25, 2021)

Again, all one has to do is follow the instructions in the owners manual pertaining to 'regen'. It's clearly explained there and what to expect and not to expect. Far as owners manuals go, every manufacturer can provide them, if, for some reason you don't have one.

Myself, I not only have the 'owners manuals' for every tractor and implement I own but I have the Factory Workshop Manuals for them (tractors) as well and if I sell anything, the manuals go with that equipment to the new owner.

I would never consider buying any powered implements or a tractor without proper documentation. Some of my implements (like my disc mower for instance are complex and I refer to the manuals quite often for not only proper fluids but for routine maintenance like grease fitting locations and frequency of lubrication and if I have a question concerning any of the, I call my dealer and they will explain it.

I don't deviate from that. Never will.


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