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Discussion Starter #1
I have a 1983 318 that runs very good, the other day while I was cutting the grass the PTO stoped working. Long story short, I’ve checked all the wiring and it’s good, the PTO switch is good and I ohmed out the coil on the pto and checked the air gap and all is right. The only other thing I think it could be is the TDCM but I’m not sure if the PTO function runs through that box.

So does the TDCM directly control the PTO?

Ive read it could be a diode inside that box that goes bad but I’d rather replace the box if possible. I’ve looked at one of the popular online sites at used replacements but I need to know if the TDCM directly runs the PTO.

Also can’t seem to find any new box’s on the interwebs. Do any of you gentlemen know where a fella could pick up a new box?
 

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Joe,

Yes, the TDCM does control the PTO functions, and often an open diode is the root cause of failures inside the TDCM. Deere can supply the TDCM but it is very expensive. I am not sure I would trust a used one that I did not take out of a working tractor myself and would question why it was removed...

You can buy a new module from a Deere parts dealer on-line for about $350, so be sure that your issue is really in the TDCM before springing for that much money...

Read through the many threads here on how to troubleshoot your issue to be sure. Here is a guide of what the functions of the TDCM are as viewed as a black box by external voltage measurements, etc.
TDCM voltage measurements.jpg


Chuck
 

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Discussion Starter #3
Thank you for all the great info chuck. I forgot to mention in my original post that with the tractor running im only getting about 1.5 to 2 volts at the PTO wiring harness connection at the front of the tractor.
 

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Could be a poor connection or it could still be in the TDCM, so do the diagnostics and address the less costly potential issues with the wiring first and only consider the expensive TDCM if all measurements point to it being the culprit. If it is an internal diode failure, then we can get more specific on how to find and replace.

Chuck
 
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