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Vehicle type

Tractor and ag equipment diesel troubleshooting

John Deere, Kubota and other modern tractors use DPF and often DEF systems, plus all the usual fuel, cooling and cold-start issues.

Green John Deere 6R 185 tractor at a farm show
A John Deere 6R tractor. Photo: MarcelX42, CC BY-SA 4.0 (resized), via Wikimedia Commons.
Orange Kubota M6060 tractor working in a vegetable field
A Kubota M-series tractor. Photo: JoachimKohler-HB, CC BY-SA 4.0 (resized), via Wikimedia Commons.

Pages for tractors / ag

Starting

Why is my Cummins hard to start when it is cold?

CumminsAll dieselsPickupsSemi trucksRV / diesel pushers+ moreTroubleshoot →
Starting

My diesel cranks but will not start. Where do I begin?

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Smoke

What does white smoke from my diesel mean?

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Smoke

Why is my diesel blowing black smoke?

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Smoke

What does blue or gray-blue smoke from a diesel mean?

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Power & drivability

Why did my diesel lose power or go into limp mode?

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Power & drivability

Why does my diesel idle rough or miss?

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Fuel system

My water-in-fuel light came on. What should I do?

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Fuel system

Why is my diesel oil level rising, and does it smell like fuel?

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Cooling

My diesel is losing coolant with no visible leak. Why?

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Emissions

What is DPF regeneration and why does my truck keep doing it?

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Fuel system

Did my diesel fuel gel? How do I prevent it?

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Emissions

Why does my diesel say DEF fault or "speed limited"?

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Emissions

How do I know if my diesel NOx sensor is bad?

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Emissions

Can a clogged EGR valve cause rough running and low power?

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Power & drivability

Why is my diesel turbo whistling or hissing under load?

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Power & drivability

What causes a diesel knock or injector "nailing" noise?

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Starting

How do I know if my glow plugs or grid heater have failed?

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Fuel system

Can a plugged fuel filter cause low power on a diesel?

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Fuel system

How does air get into diesel fuel lines, and how do I fix it?

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Power & drivability

How much oil should my diesel use, and when is it too much?

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Power & drivability

How do I tell if my diesel has excessive blow-by?

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Cooling

What is cavitation and liner pitting in a diesel cooling system?

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Guides & checklists

What maintenance does a diesel need that a gas engine does not?

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Guides & checklists

How do I get my diesel ready for winter?

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Emissions

Is it legal to delete the DPF, EGR or DEF on my diesel?

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Emissions

My tractor wants a parked regen or says DEF low. What do I do?

Tractors / agTroubleshoot →

Where this comes from

Last reviewed 2026-10-19. General information only: confirm with your service information and a qualified diesel technician.