Diesel Exhaust Fluid vs Engine Oil – Don’t Confuse Them

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Two fluids, two completely different systems

Know Where DEF and Engine Oil Go—and What to Do After a Wrong Fill

Diesel Exhaust Fluid (DEF) is a water-based emissions fluid that goes into a dedicated DEF tank and is injected into the exhaust after the engine. Engine oil is a petroleum-based or synthetic lubricant that goes into the engine crankcase and circulates through bearings, pistons, camshafts and the turbocharger.

DEF is not diesel fuel, an oil additive, coolant or engine cleaner. Engine oil must never be poured into the DEF tank, and DEF must never be poured into the engine-oil opening. A wrong fill can become much more expensive once the engine is started.

DEF goes into A separate tank, commonly identified by a blue cap
Engine oil goes into The engine oil-fill opening under the hood or service panel
DEF’s job Help the SCR exhaust system reduce nitrogen-oxide emissions
Engine oil’s job Lubricate, cool, clean and protect internal engine components
Compare the fluids Wrong fluid emergency Identify the caps
Read the cap before pouring Confirm “DEF/AdBlue,” “engine oil” or “diesel fuel” every time—even when the caps are close together.
Use dedicated equipment Never share funnels, pumps, jugs or transfer hoses between DEF, oil, fuel and coolant.
Stop after a wrong fill Do not start the engine. Keep the ignition off and arrange professional draining and inspection.
The direct answer

What Is the Difference Between DEF and Engine Oil?

DEF

Diesel Exhaust Fluid

DEF is an aqueous solution made for diesel vehicles with selective catalytic reduction, or SCR. Road-vehicle DEF contains approximately 32.5% high-purity urea and 67.5% purified water.

  • Stored in a separate DEF tank
  • Injected into the hot exhaust stream
  • Does not lubricate the engine
  • Does not mix with diesel fuel
  • Commonly called AdBlue in Europe and other markets
  • Generic technical name: AUS 32
  • Should meet ISO 22241 quality requirements
VS
OIL

Diesel Engine Oil

Engine oil is a lubricant formulated from base oils and additives. It circulates through the engine to reduce friction, carry heat, control deposits and protect moving components.

  • Poured through the engine oil-fill opening
  • Stored primarily in the oil pan or sump
  • Circulates through the oil pump and filter
  • Lubricates bearings, pistons and valve-train parts
  • Protects the turbocharger where applicable
  • Uses viscosity grades such as 5W-40 or 15W-40
  • Must meet the engine’s API, ACEA or OEM specification
Never mix them. DEF contains water and urea, so it cannot lubricate an engine. Engine oil contains hydrocarbons and additives that can severely contaminate a sensitive DEF dosing and catalyst system.
Side-by-side reference

DEF vs Engine Oil Comparison Chart

Feature
Diesel Exhaust Fluid
Engine Oil
Main purpose
Reduce nitrogen-oxide emissions in the SCR exhaust system
Lubricate, cool, clean and protect internal engine parts
Where it works
Downstream of the engine in the exhaust aftertreatment system
Inside the engine lubrication system
Typical composition
32.5% high-purity urea and 67.5% purified water
Mineral, synthetic or blended base oil plus an additive package
Appearance
Normally clear and colourless
Usually amber when new and darker after use
Fill location
Dedicated DEF or AdBlue filler, often with a blue cap
Oil-fill cap on the engine under the hood or service cover
Storage system
Separate DEF tank, pump, heater, lines and injector
Oil pan, pump, galleries, cooler and filter
Consumed during use
Yes, it is dosed into the exhaust and must be refilled
Normally recirculated, although some consumption between changes can occur
Routine maintenance
Refill when low and use clean, on-spec fluid
Change at the prescribed mileage, time, hours or oil-life interval
Cold behaviour
Freezes near 12°F / −11°C; vehicles commonly include a heating system
Thickens in cold weather; correct SAE viscosity supports cold starting
Quality standard
ISO 22241 / AUS 32; API certification is commonly used in North America
Vehicle-specific API, ILSAC, ACEA or manufacturer approval
Can it go in the fuel tank?
No
No, unless a manufacturer specifically authorizes a product or procedure—which normal road vehicles generally do not
DEF never enters normal combustion

What Does Diesel Exhaust Fluid Actually Do?

The diesel engine burns fuel. Combustion produces exhaust gases that can contain nitrogen oxides, commonly written as NOx.
The exhaust travels through the aftertreatment system. The path may include a diesel oxidation catalyst, diesel particulate filter and SCR catalyst, depending on the vehicle.
The DEF injector sprays a measured amount into the exhaust. The control system adjusts dosing according to engine load, temperature, exhaust flow and sensor information.
Heat converts the urea into ammonia. The chemical reaction happens in the exhaust system—not in the fuel tank or engine crankcase.
The SCR catalyst reduces NOx. The system converts much of the nitrogen-oxide pollution into nitrogen and water vapour.
DEF is not a performance additive. Pouring it into diesel fuel or engine oil does not improve combustion, clean injectors, reduce friction or increase fuel economy.

API micro-steps: Open the official DEF page, review the “DEF (AUS 32)” section and look for the API certification mark when purchasing packaged fluid in North America.

Read official API DEF guidance
Oil protects the engine internally

What Does Diesel Engine Oil Do?

1

Reduces friction

Oil creates a protective film between moving surfaces such as crankshaft journals, bearings, camshaft components and piston-related parts.

2

Carries heat

Oil absorbs heat from internal components and transports it toward the oil pan or oil cooler.

3

Controls deposits

Detergent and dispersant additives help suspend soot and contaminants so they can be trapped by the oil filter or removed during an oil change.

4

Protects against corrosion

Additives help protect metal surfaces against acids, moisture and oxidation by-products.

5

Supports turbo lubrication

Many diesel turbochargers depend on a clean, correctly specified supply of pressurized engine oil.

6

Helps seal combustion pressure

The oil film around piston rings contributes to sealing while also reducing cylinder and ring wear.

Correct quantity is not enough. Diesel engine oil must also have the correct SAE viscosity and API, ACEA or manufacturer approval for the engine and emissions system.
Check the label, not just the colour

How to Identify the DEF, Engine-Oil and Diesel-Fuel Fillers

DEF

DEF or AdBlue filler

Often uses a blue cap marked “DEF,” “AdBlue,” “AUS 32” or an emissions-fluid symbol.

It may be beside the diesel filler, behind a separate door, under the hood or in another vehicle-specific location.

OIL

Engine-oil filler

Usually located on top of the engine and marked with an oil-can symbol, “engine oil” or a viscosity reference.

It is normally accessed under the hood rather than through the external fuel door.

DIESEL

Diesel-fuel filler

Normally marked “diesel fuel only” or with a fuel-pump symbol.

It may sit beside the DEF filler, which makes reading both labels essential.

Colour is a clue, not proof. Blue is widely used for DEF, but cap design and location vary by manufacturer and market. Read the moulded or printed wording before opening a container.
  • Keep DEF containers closed until you reach the correct filler.
  • Keep engine oil in its original labelled container.
  • Do not place open DEF and oil containers beside each other.
  • Use different funnels with permanent labels.
  • Clean the filler area before opening the cap.
  • Check the owner’s manual when the cap location is unclear.
Wrong fluid? Stop before turning the key

What to Do If DEF and Engine Oil Are Mixed Up

Universal first action: Do not start the engine, do not switch the ignition on unnecessarily and do not attempt to “dilute” the mistake with the correct fluid. Secure the vehicle and contact the manufacturer, dealer, fleet maintenance provider or qualified diesel technician.

! DEF poured into the engine-oil filler

Do not start the engine. Do not rotate it to “mix” or circulate the fluid.

DEF contains a large amount of water and cannot maintain an engine’s lubricating film. Urea and water can contaminate the oil, promote corrosion and reach bearings, the turbocharger and oil galleries if the engine is started.

  • Leave the engine off.
  • Record approximately how much DEF was added.
  • Do not rely on draining only a small amount from the pan.
  • Arrange towing or on-site service.
  • Expect the oil and filter to be replaced.
  • Allow the technician to decide whether additional draining, flushing, sampling or inspection is required.

If the engine was started: Shut it off immediately and do not restart it. Tell the technician how long it ran and whether an oil-pressure warning or unusual noise appeared.

! Engine oil poured into the DEF tank

Do not start the engine or operate the vehicle.

Even a small amount of petroleum-based contamination can damage DEF pumps, filters, injectors, sensors and the SCR catalyst. Adding more DEF does not restore purity.

  • Keep the ignition off.
  • Do not attempt to siphon and reuse the fluid.
  • Do not add water or more DEF.
  • Use a tow or qualified mobile service.
  • Tell the technician what oil was added and approximately how much.
  • The DEF tank and affected components may require draining, cleaning, testing or replacement.

If the engine was started: Shut it off and obtain service immediately. Starting may circulate contaminated fluid through more of the SCR dosing system.

! DEF poured into the diesel-fuel tank

Do not start the engine. This is a fuel-system emergency.

DEF is water-based and can damage high-pressure fuel pumps, injectors, lines and rails. Modern common-rail diesel systems are especially sensitive to water and non-fuel contamination.

  • Do not turn the ignition on when it could activate an electric fuel pump.
  • Do not attempt to drive to a repair shop.
  • Arrange professional tank draining and fuel-system inspection.
  • Report whether the engine was started or driven.
  • Keep the receipt or container so the fluid can be identified.

If the engine was started: Shut it off as soon as safely possible and tow the vehicle. Repair requirements may increase after contaminated fluid reaches the high-pressure system.

! Diesel fuel entered the DEF tank

Do not start or continue operating the vehicle.

Hydrocarbon contamination can damage the DEF tank, pump, seals, dosing equipment and catalyst. The fluid cannot be corrected by adding more DEF.

  • Stop filling immediately.
  • Do not attempt to mix or stir the tank.
  • Do not drain the fluid into an unlabelled container.
  • Arrange professional service.
  • Use dedicated DEF handling equipment during repair.

If the truck has already been driven: Have the complete DEF system evaluated for petroleum contamination.

Do not use a generic “flush recipe.” The repair procedure depends on the vehicle, fluid quantity, whether the engine was started and which pumps, lines or injectors were exposed.
Fast emergency reference

Wrong-Fluid Response Matrix

Mistake Immediate risk Correct response
DEF in engine oil Loss of lubrication, water contamination and internal corrosion Do not start. Tow or service in place. Drain, inspect and follow the engine manufacturer’s repair procedure.
Engine oil in DEF tank Petroleum contamination of SCR pump, injector, sensors and catalyst Do not start. Do not dilute. Professionally drain and evaluate the DEF system.
DEF in diesel tank Water-based contamination of high-pressure fuel components Do not start or switch on. Arrange tank draining and fuel-system inspection.
Diesel in DEF tank Hydrocarbon damage to DEF-system materials and catalyst Do not operate. Drain and service with dedicated DEF equipment.
Water added to DEF Incorrect urea concentration and possible dosing or catalyst faults Do not assume distilled water is harmless. Have the contaminated tank serviced.
DEF added to coolant Cooling-system contamination, deposits and corrosion risk Do not start. Arrange cooling-system draining and inspection.
Oil added to diesel fuel Incorrect fuel properties, emissions-system deposits and injector problems Do not rely on old two-stroke practices. Follow the vehicle manufacturer’s fuel-contamination procedure.
Correct DEF refill procedure

How to Add Diesel Exhaust Fluid Safely

Confirm that the vehicle requires DEF. Use the owner’s manual and dashboard information. Older diesels and engines without an SCR system may not use DEF.
Buy the correct road-vehicle fluid. Look for DEF, AdBlue or AUS 32 meeting ISO 22241. In North America, check for the API DEF certification mark.
Check the date and container condition. Do not use a leaking, unsealed, badly swollen, dirty or expired container.
Park safely and switch the engine off. Use a ventilated area away from food, children and unnecessary traffic.
Locate the dedicated DEF filler. Read the cap. Do not assume that the filler beside the diesel opening is always DEF.
Clean around the filler neck. Prevent dust, fuel, grease and oil from entering the tank.
Use a dedicated nozzle or sealed container spout. Never use a funnel that has handled engine oil, diesel fuel, coolant or washer fluid.
Fill slowly and stop at automatic shutoff. Do not continue topping off after a pump nozzle clicks or the container stops flowing.
Replace the cap securely. Wipe the filler area and confirm that the diesel-fuel cap or door was not disturbed.
Clean spills promptly. Rinse small exterior spills with water. If white crystals have formed, use warm water and a clean sponge.
Allow the gauge time to update. The level display may not change immediately, especially in very cold conditions or after a small refill.
Do not overfill a freezing DEF tank. DEF expands when frozen. Vehicle tanks are designed for cold operation, but overfilling can remove the expansion space and damage the tank.

Ram micro-steps: Open the official fill procedure, compare the illustrated DEF and diesel locations, check the portable-container limit for the specific truck and stop at the first automatic shutoff.

View the official Ram DEF fill procedure
Correct engine-oil top-off procedure

How to Add Diesel Engine Oil Without Overfilling

Confirm that the engine is actually low. Park on level ground and use the warm/cold and waiting-time procedure specified in the owner’s manual.
Identify the correct engine oil. Match the required SAE viscosity and API, ACEA or manufacturer approval—not only the brand.
Open the engine-oil filler. Verify the oil-can symbol or “engine oil” label. Do not open the nearby coolant, brake-fluid or DEF reservoir.
Use a clean oil-only funnel. A funnel contaminated with DEF, coolant, dirt or fuel should not be used.
Add a small amount. Start with approximately 0.25–0.5 US quart, or 250–500 ml, unless the dipstick and manual clearly indicate a larger shortage.
Wait and recheck. Allow the oil to drain into the sump, then read the dipstick again using the same procedure.
Stop within the approved range. Do not aim above the full or maximum mark.
Investigate repeated low levels. Frequent topping off may indicate a leak, turbocharger issue, worn engine, crankcase-ventilation problem or another fault.
Do not pour DEF into the engine because the oil level is low. DEF adds no lubrication and can cause immediate internal damage once circulated.
The dashboard separates the systems

DEF Warnings vs Engine-Oil Warnings

Warning or message
What it normally means
What to do
DEF level low
The separate DEF tank needs approved fluid
Refill with the minimum amount required by the manual. Do not add engine oil or diesel fuel.
Incorrect DEF or poor-quality DEF
The system detected wrong concentration, contamination or an SCR fault
Do not keep adding random fluid. Obtain diagnosis before speed or restart restrictions occur.
Service DEF system
A sensor, heater, pump, injector, quality or catalyst-related fault may exist
Follow the message and arrange service. A full tank does not prove the system is healthy.
Red oil-pressure lamp
The engine may not have adequate lubricating-oil pressure
Stop safely and shut the engine off immediately. Check the oil level, but do not assume adding oil will fix a pressure-system fault.
Oil level low
The engine-oil level may need checking and topping off
Use the approved level-check procedure and add the exact engine oil gradually.
Change engine oil soon
The engine-oil service interval is approaching
Schedule an oil-and-filter change. Filling the DEF tank does not reset or satisfy this maintenance requirement.
Speed limited or no restart countdown
DEF is empty, contaminated or the SCR system has an unresolved fault
Follow the exact dashboard instruction. Required refill quantities and restrictions vary by vehicle.
Important difference: A low DEF warning usually relates to emissions-system operation. A red oil-pressure warning relates to possible engine lubrication failure and normally requires immediate shutdown.
DEF cleanliness is critical

Why DEF Is More Sensitive to Contamination Than It Looks

DEF may resemble clear water, but it is manufactured to a controlled concentration and purity standard. Tap water, agricultural urea, fuel, oil, coolant, rust, dust and dirty transfer equipment can make the fluid unsuitable for an SCR system.

Oil contamination

Petroleum can attack system materials, foul dosing components and poison the catalyst. A funnel with an oily film is not clean enough for DEF.

Tap-water contamination

Minerals and metals can create deposits and alter the required solution concentration. Do not dilute DEF with tap water.

Dirt contamination

Dust and debris can block filters, damage pumps and restrict the fine DEF injector nozzle.

Fuel contamination

Even a small petroleum-based contamination can create a major DEF-system repair.

Expired or overheated fluid

Long storage at high temperatures can shorten DEF life and change quality.

Reused containers

A container that previously held oil, fuel or coolant should never be repurposed for DEF.

  • Buy sealed, correctly labelled DEF.
  • Check the API certification mark where applicable.
  • Keep the cap tightly closed.
  • Store away from direct sunlight and excessive heat.
  • Use first-in, first-out stock rotation in fleets.
  • Use dedicated pumps, hoses, nozzles and funnels.
  • Do not return drained DEF to the vehicle.
  • Do not mix old and new fluid when contamination is suspected.

API purchasing micro-steps: Check the container for the API DEF mark and expiration information, then use API’s licensee directory when the brand or supplier is unfamiliar.

Review API DEF quality and storage guidance
Freezing DEF is normally expected

What Happens When DEF Freezes?

On-spec road-vehicle DEF begins freezing near 12°F / −11°C. Modern SCR-equipped vehicles are designed with tank and line heating strategies so the frozen fluid can thaw during operation.

What you should do

  • Leave the fluid in the vehicle’s DEF tank.
  • Allow the factory heating system to operate.
  • Keep enough expansion space in the tank.
  • Expect a delayed gauge update in very cold weather.
  • Follow model-specific cold-weather instructions.

What you should not do

  • Do not add antifreeze.
  • Do not add water.
  • Do not add engine oil or fuel.
  • Do not apply an open flame or uncontrolled heater.
  • Do not overfill the tank before freezing weather.
Freezing does not turn DEF into engine oil. Once correctly thawed, on-spec DEF returns to its working solution. No lubricant should be added to prevent freezing.
Clean each spill differently

How to Clean DEF and Engine-Oil Spills

DEF spill

Use water promptly

  • Wear gloves and avoid eye contact.
  • Rinse small exterior spills with clean water.
  • Use warm water and a sponge for dried white crystals.
  • Do not allow concentrated fluid to remain on painted, metal or electrical components.
  • Absorb larger ground spills and follow local disposal rules.
  • Ventilate the area if an ammonia-like odour is noticeable.
Engine-oil spill

Contain and absorb it

  • Stop the source and place a drain pan underneath.
  • Use absorbent granules, pads or suitable material.
  • Collect contaminated absorbent for proper disposal.
  • Use an appropriate degreaser on compatible surfaces.
  • Do not hose oil into a storm drain, soil or waterway.
  • Take used oil to an approved recycling or collection point.
Do not clean an oil spill by washing it into the street. Water may move the oil, but it does not make the petroleum contamination disappear.
Prevent workshop mix-ups

DEF and Engine-Oil Storage Checklist

Store DEF correctly

  • Keep it in a sealed original or approved dedicated container.
  • Protect it from direct sunlight and excessive heat.
  • Check the labelled storage-temperature range.
  • Mark bulk tanks, pumps and hoses “DEF ONLY.”
  • Use dust caps on couplings and nozzles.
  • Do not store it in a previously used oil drum.
  • Rotate stock and check expiration information.

Store engine oil correctly

  • Keep containers sealed and clearly labelled.
  • Separate new oil from used oil.
  • Mark the viscosity and OEM specification.
  • Use dedicated pumps and funnels.
  • Prevent water, DEF, fuel and dust from entering.
  • Keep containers away from floor drains.
  • Use spill containment for drums and bulk tanks.
Fleet colour-coding system: Use blue labels and dedicated blue-handled equipment for DEF, brown or black labels for engine oil, green labels for coolant and yellow labels for diesel fuel—but always keep written names on every container.
Common misconceptions corrected

DEF and Engine-Oil Myths

“DEF is a diesel additive.”

False. DEF is stored separately and injected into the exhaust. It should never be mixed with diesel fuel.

“DEF lubricates injectors.”

False. DEF can damage fuel-system components if it enters the diesel tank.

“A little engine oil will not hurt DEF.”

False. Petroleum contamination can damage sensitive SCR components even at a very low concentration.

“Water can replace DEF temporarily.”

False. Water does not contain the required urea concentration and may trigger quality faults or damage.

“Frozen DEF must be replaced.”

Usually false. On-spec DEF is designed to freeze and thaw, and vehicle systems commonly include heaters.

“Filling DEF also services the engine oil.”

False. DEF refilling and engine-oil maintenance are completely separate tasks with separate gauges and intervals.

International names and standards

DEF, AdBlue and AUS 32: Are They the Same?

Name
Where commonly used
What it means
Buying guidance
DEF
United States, Canada and other markets
Diesel Exhaust Fluid for road-vehicle SCR systems
Look for ISO 22241 compliance and the API certification mark where applicable.
AdBlue
Europe and many international markets
A widely used trademark for qualifying AUS 32 fluid
Use a reputable product meeting the vehicle manufacturer’s required standard.
AUS 32
Technical and international documentation
Aqueous Urea Solution containing 32.5% urea
This is the generic technical designation used in ISO 22241.
ARLA 32
Brazil and parts of Latin America
Regional name for 32.5% urea SCR fluid
Confirm the recognised local standard and vehicle requirement.
Marine DEF / AUS 40
Marine and selected large-engine applications
A different 40% urea solution for specified systems
Do not use AUS 40 in a road vehicle requiring AUS 32.
Do not buy by the word “urea” alone. Agricultural fertilizer solution, homemade mixtures and marine AUS 40 are not substitutes for road-vehicle DEF/AUS 32.
Ten-second pre-fill check

Use This Checklist Before Adding Any Diesel-Truck Fluid

Check the vehicle

  • Which dashboard warning appeared?
  • Which system actually needs fluid?
  • Where is the correct filler?
  • What does the cap say?
  • Does the manual match the vehicle year and engine?

Check the container

  • Is it DEF, engine oil, diesel fuel or coolant?
  • Is the seal intact?
  • Is the specification correct?
  • Is the container clean and within date?
  • Is the funnel or nozzle dedicated to this fluid?
Simple rule to remember Blue DEF cap → exhaust system | Oil-can cap → engine lubrication | Diesel label → fuel tank
Best practical habit: Hold the labelled container beside the labelled filler and read both out loud before pouring. This five-second check can prevent a major repair.
DEF and engine-oil FAQs

Frequently Asked Questions

Is Diesel Exhaust Fluid the same as engine oil?

No. DEF is a 32.5% high-purity urea solution in purified water used by the SCR exhaust system. Engine oil is a lubricant that circulates inside the engine. They are not interchangeable and must never be mixed.

Does DEF go inside the diesel engine?

No. DEF is stored in a separate tank and injected into the exhaust stream after combustion. It does not belong in the engine crankcase, diesel-fuel tank, coolant reservoir or oil-fill opening.

What should I do if I put DEF in the engine-oil filler?

Do not start the engine. Keep the ignition off, record how much was added and arrange professional service or towing. The oil and filter will normally need replacement, and the technician should determine whether further draining, flushing or inspection is required.

What happens if engine oil goes into the DEF tank?

Engine oil can contaminate the DEF pump, lines, injector, quality sensors and SCR catalyst. Do not start the vehicle, do not dilute the tank with more DEF and arrange professional draining and inspection.

What happens if DEF is put in the diesel-fuel tank?

DEF can severely damage high-pressure fuel pumps and injectors because it is water-based and not a fuel. Do not start the engine or switch the ignition on unnecessarily. Have the fuel tank and system professionally drained and inspected.

Can water be used instead of DEF?

No. Water does not contain the required urea concentration and can trigger incorrect-fluid faults, deposits, poor emissions conversion and component damage. Use only on-spec DEF/AUS 32.

Is AdBlue the same as DEF?

AdBlue is a widely used trademark for qualifying AUS 32 fluid and is functionally the same type of road-vehicle SCR fluid commonly called DEF in North America. Confirm ISO 22241 compliance and the vehicle manufacturer’s requirement.

Can DEF freeze without being damaged?

Yes. On-spec DEF freezes near 12°F or −11°C and is designed to thaw back to its working concentration. Modern vehicles commonly heat the DEF tank and lines. Do not add water, oil, fuel or antifreeze to stop freezing.

Why does my truck need DEF but also need oil changes?

The fluids perform separate jobs. DEF treats exhaust emissions and is refilled as it is consumed. Engine oil lubricates the engine and must be changed with its filter according to the prescribed mileage, time, engine-hours or oil-life schedule.

How can I prevent DEF and oil from being mixed up?

Read both the container and filler label, keep DEF and oil containers physically separated, use dedicated colour-coded funnels and pumps, keep fluids in original packaging and train every driver or technician on the fill locations.

Official technical references

Sources Used for This Guide

Fill locations, warning sequences, minimum refill quantities and repair procedures vary by vehicle. Recheck the current owner’s or service manual for the exact model year and engine.

Last technical-source review: July 30, 2026.

Independent maintenance information: EngineOil-Capacity.com is an independent informational website. It is not a vehicle manufacturer, engine manufacturer, oil company, DEF supplier, dealership or repair facility. Wrong-fluid repair requirements vary according to the vehicle, contamination amount and whether the engine was started. When DEF, fuel, coolant or engine oil enters the wrong system, keep the engine off and obtain model-specific professional guidance. Shut the engine off immediately if an oil-pressure warning remains on, a major leak appears or serious engine noise begins.