Ask the Mechanic

Steve Thompson, Contributing Columnist

READER: I have a John Deere 7800 that occasionally has two lights that come on in the dash, a red light and a yellow flashing light. It does not matter if the hydraulic oil is hot or cold. The red light shows that the hydraulic oil pressure is low, and the yellow light is a warning light. The hydraulic oil level is good, the hydraulics are strong, and the lights still come on -- but only when the tractor is under a heavy load. It will stay off during the time I am just cruising through the field with the field cultivator, but after I make the turn and drop the field cultivator and instantly load the tractor, the lights come on with no hydraulic demands but go off after I move away from the turn. I have changed the hydraulic filter, but it made no change.

STEVE: Most of the time if you feel that the hydraulics are strong in all areas of the tractor, and the hydraulic pressure light comes on, the problem will be found in the hydraulic pressure sensor. This sensor unit is located at the manifold of the hydraulic filter (see photo accompanying this article). It's easy to change, and I would recommend giving that a try.

(Editor's Note: The farmer responded that the sensor fixed his tractor.)

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-- Email Steve Thompson care of askthemechaniccolumn@gmail.com, and be sure to include your contact information and phone number.

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