John Deere 7800 Low transmission oil pressure warning light
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Thread: John Deere 7800 Low transmission oil pressure warning light

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    John Deere 7800 Low transmission oil pressure warning light

    Hello. Last September, my friend bought a JD 7800 Powrquad for his 60 hectare farm. The tractor is mainly used for ploughing and cultivating. Last autumn and this spring it had no problems towing a 5 furrow reversible plough and cultivating with a 6 meter cultivator. However, a couple of days ago, the alarm beep started to sound and the instrument panel started to show "Transmission Oil Pressure" and "Stop Engine" lights when ploughing.

    The warning light is not on all the time, it only starts to flash after ploughing for around an hour. Sometimes sooner, sometimes later. Some days the warning light and alarm beep won't appear until the evening, even though the tractor was started and running from afternoon. Also, it is only blinking when the plough is raised up and the engine is running at idle. When you lower the plough into the soil and the engine is running idle, the warning light still flashes and the alarm beeps. But if you rev it up, the warning light disappears for as long as you hold the revs higher. My friend can actually plough as long as he holds the revs high enough. When it's time to raise the plow, and the RPMs drop to the idle, the alarm and warning light comes back.

    Other than that, the tractor seems to be working as normal. All the ranges, gears seem to work as intended, there is no loss on power, 3 point hitch raises/lowers the implements just fine.

    When my friend bought this tractor, there was some oil leakage through Auxiliary Steering Pump seals, but there were no warning lights flashing whatsoever. We have replaced those seals last week, and it seems that there still is some minor oil leakage, but nothing excessive – something like an oil sweat after a whole day of working in the fields. The leakage was definitely bigger when the tractor was bought.

    We have already changed transmission and hydraulic oil filters, we have also cleaned the suction screen in the differential housing. The hydraulic oil has been changed last year, if I recall correctly.

    The guy from local John Deere dealer checked the transmission pressure and he said that is is close to ideal. If I remember correctly, the oil wasn't hot when the pressure was checked. Would it be better to check the pressure when the oil is hot?

    When we put back the hydraulic oil after changing the filters and cleaning the suction screen, we have filled it to the upper mark with a 3 point hitch in the lowest position, just as the manual says. Few days ago somehow the oil level was a bit higher than the upper mark. Could we have somehow put too much oil?

    Diagnostic mode shows only one code: CCU 026.
    I've also checked the hydraulic oil temperature via CCU when the tractor was hot, and the hydraulics temperature was 77-78 Celsius.

    The dash shows a bit more than 10,000 hours on this tractor. We live in Eastern Europe.

    Is the sensor the next step we should look at?
    Last edited by Yamahahonda; 09-05-2019 at 03:52 PM.

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    johnH123's Avatar
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    If the actual pressure is good, then I would just go ahead and replace the sensor. it should be cheap enough.
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    The original sensors have a history of failing. If yours is original, I am surprised it lasted this long. The original sensor used 30 mm wrench to remove, the replacement uses 9/16" wrench or 14mm. New part number is RE212870. Sensor is located above transmission filter. First above filter is filter restriction sensor, next above that is pressure sensor. Also, it is best to check pressure when oil is hot.
    Last edited by jd110; 09-05-2019 at 08:45 PM.

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    Quote Originally Posted by johnH123 View Post
    If the actual pressure is good, then I would just go ahead and replace the sensor. it should be cheap enough.
    We'll probably check the pressure again, only this time when the oil is hot. If all is good, then we will replace the sensor.


    Quote Originally Posted by jd110 View Post
    The original sensors have a history of failing. If yours is original, I am surprised it lasted this long. The original sensor used 30 mm wrench to remove, the replacement uses 9/16" wrench or 14mm. New part number is RE212870. Sensor is located above transmission filter. First above filter is filter restriction sensor, next above that is pressure sensor. Also, it is best to check pressure when oil is hot.
    Thank you for your help, this information is really useful. We'll try to replace the sensor and hopefully this will fix the problem.

    Also, do you by any chance know what the pressure readings of the transmission should be?
    johnH123 likes this.

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    Pressure spec is 245 - 265 psi.
    DRobinson likes this.

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    Quote Originally Posted by jd110 View Post
    Pressure spec is 245 - 265 psi.
    Thank you.

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