What's built not to be repaired, is bad value for money.
What I don't understand is, if this sensor fails so often, why doesn't the farmer keep one in stock. That he's willing to have the machine idle for 2 days to get it suggests this isn't a really big problem for him.
Probably because it's impossible as JD as only vendor only sells the part to authorized service shops, with contracts forbidding sale to individual customers (edit: and the sensor is likely patented too, to prevent clones, like Apple did with Magsafe).
Or worse, each sensor/component has a UUID and registers with the ECU over the communication bus... and to allow the sensor to be used with the ECU, it has to be authorized with a key provided only to authorized service shops.
The issue is that the OBD standards have a mode for restricting access (0x27) until the test equipment has passed a challenge-response phase. The exact method varies but it is often a fairly simple scheme such as multiplying a secret key by a random value and returning part of the product for the ECU to confirm. The keys can be discovered by reverse engineering firmware or capturing enough initialization packets to work out the system. One of my ECUs from a defunct manufacturer has the ever original 0x6789 as its key.
For starters, even the text of the article shows that he's reliant on the technician to replace the part, and it doesn't break down what of the 2 days is ordering the part vs scheduling the technician's time. It may be that even with the part in hand it's 2 days for an opening in the tech's schedule.
Further, while the article makes it sound as if there is one part repeatedly failing, the reality is that there are dozens of different sensors, and maybe only one fails per year. Your proposed solution might require the farmer to have thousands of dollars in spare parts sitting around at all times so he has replacements ready for all of them. Modern ag is already a capital intensive operation without forcing every family farm to double as a parts warehouse.
Going to the text I was working off:
"It takes a technician at least two days to order the part, get out to the farm, and swap out the sensor."
"Order the part" sure doesn't sound like a same day thing. Maybe this only shaves off one day on average. But I can't see how it doesn't shave off some time.
I grant you your last point; if this isn't a single lemon(ny) part prone to failure he's getting unacceptable service. And I predict this gambit will not end well for John Deere.
This is just a guess since that passage is vague, but it sounds to me like he isn't able to order the part himself. It might be a proprietary thing that only a (John Deere approved) tech can order. Either that, or maybe he isn't able to overcome some kind of anti-tampering hardware to install it himself.
"But the crops are so ugly, and it took me 3 months to setup"
"but it was free!"
As part of:
http://opensourceecology.org/wiki/Global_Village_Constructio...
(I have no idea whether the stuff they are making is practical or not)