I'm betting that on the tier iv final machines the engine module will shut down and you need to refill before starting up again because what's the point of a dpf and all that trouble if the machine will run without it? Now bypassing the dpf is another topic. I don't have any tier iv final machines and will avoid it as long as I can. Tractors are getting very complicated and expensive and no longer can you plan on keeping a machine for 30 years and maintaining it yourself for long term cost traction. The mfgs want you to be paying them for the rest of time and not just for parts anymore. Service is their big business now.