Yes. I have a problem child L3301 in the shop.
First, the dealer should re-flash the ECU. 99.9% of the time, this will solve the issue. The original program would set a PO336 code if the engine RPM was to drop below I think 700 RPM without shutting off the key. The new program has addressed this and dropped that threshold to a much lower RPM, so that if you're, say, running the tractor into a tree to push it over and the engine RPM drops because of loading, it is much less likely to set the code.
PO336 is a crankshaft abnormality code. It can be set by a number of different things, ranging from the actual sensor having a problem to a simple wire harness or connector problem to foreign material on the sensor itself. And each of those issues need to be addressed as part of diagnosis. The sensor cannot be tested by Kubota special tools. Perhaps the automotive industry would be able to do it, but most Kubota dealers don't have that type of tooling. Kubota is currently using Diagmaster to do all of the diagnostic stuff on the CRS and Tier 4 tractors.
There is a DIY way of clearing the code from the dash panel, but it does not clear it from the ECU. And you want to have it cleared from both the ECU and the panel. When the code is set, the tractor's horsepower is de-rated. Also, you'll notice a rougher running engine and some slight injector knock at a slow idle. The code, if stored and continued to run, can also affect the DPF negatively, so ideally you'll want to get it fixed as soon as possible to avoid problems relating to the DPF and DOC.
IF it's been re-flashed with the new programming, and you're still seeing the code....then there are several possibilities. One, the sensor itself is dirty. IF you have a front end loader, the loader has to come off (if it's an LA525, it comes off in 30 seconds if you're quick), then the right side loader frame needs to be removed, and the valve. The sensor is right behind the loader frame, has a harness going to it and a plug. 6mm (10mm socket) holds it on the bell housing. Remove it, and check carefully for metal shavings. Sometimes the manufacturer didn't get them clean enough and because the sensor is magnetic, it will attract any loose steel or iron particles-which will "fool" the sensor's pulse going to the ECU.
If that's been done (the re-flash and cleaning of the sensor), ask the dealer to inspect the flywheel.