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John Deere dozer 850J code TCU620.4

Crooked Lakes · 2025-02-21 17:13

dozer just sitting idling to warm up and engine revved to 1925 rpm. Then seen code TCU 620.4 came up. Wher the heck do I start?

Replies22
  1. #1Simon C2025-02-21 18:54

    I see that you have 1 code. Your operators manual may tell you how to retrieve Active and Logged codes, in case there is more. Someone may chime in for where to start troubleshooting. Might be an idea to post your serial number. Simon C

  2. #2Crooked Lakes2025-02-21 19:04

    other codes Tank bypass sol no response TCU 522439.5 Fan drive sol short circuit TCU 1071.6 Ser#T0850JX117104 Talked to JD and they said should have 5 volts at blue wire T01. I tested with key on and 0 volts . Took off a cap for wiring harness near TCU in dash and did get 5 volts on T01 when cap was off.

  3. #3Simon C2025-02-21 19:08

    You probably need an electrical schematic to be able to see more clearly what is involved. Simon C

  4. #4Crooked Lakes2025-02-21 19:17

    Ok, he did say this code can go to numerous sensors. Can I guy get a schematic off the internet?

  5. #5Simon C2025-02-21 19:20

    Maybe mg2361 will see your post. He has helped out lots of people. Maybe on weekend he will see it. Simon C

  6. #6Crooked Lakes2025-02-21 19:24

    Ok and thank you for your help

  7. #7mg23612025-02-22 12:07

    @Crooked Lakes Check your messages.

  8. #8Crooked Lakes2025-02-22 12:57

    OMG, there looks like 20 possibilities! Thank you very much! Now the fun begins!

  9. #9Crooked Lakes2025-02-25 08:45

    Thanks you guys! The very bottom of one connection was in some frozen dirt. That’s all it took, cleaned it up a bit and good as new!

  10. #10Simon C2025-02-25 10:35

    Thanks for answering back, and thanks to mg2361 for the schematics. Simon C

  11. #11Crooked Lakes2025-02-25 10:38

    Absolutely!!

  12. #12Gus Mueller2025-09-01 00:22

    Crooked Lakes. My Dozer has no accelerator as of today on a job and I am getting the TCU 620.4 code. Could it be a bad connection on a sensor ?

  13. #13Gus Mueller2025-09-01 01:01

    Crooked Lakes, Do you have that test procedure that mg had sent you ...Gus

  14. #14Crooked Lakes2025-09-01 13:44

    I do, bare with me while I figure out how to bring it up

  15. #15Crooked Lakes2025-09-01 14:00
  16. #16Crooked Lakes2025-09-01 14:05

    Schematic

  17. #17Crooked Lakes2025-09-01 14:09

    One more

  18. #18Crooked Lakes2025-09-01 14:11

    Last one

  19. #19Gus Mueller2025-09-01 23:44

    Thank you Crooked Lakes, your help is greatly appreciated

  20. #20Crooked Lakes2025-09-02 08:47

    Hope it helps

  21. #21Gus Mueller2025-09-03 07:17

    Crooked Lakes, Yes you were a big help and greatly appreciated, we chased all the sensors, connectors and did find one wire rubbing going to the HIC block however the code disappeared before that . When we went to do a Calibration it failed and showed max threshold on R/S track, it never showed a speed sensor code and I carry a extra one and installed it and we are back in business. I wonder if the speed sensor was the culprit the whole time? Thank you for going out of your way to give me some help...Gus

  22. #22Crooked Lakes2025-09-03 08:56

    This forum is a great thing