From the 2013 owner's manual, diesel supplement:
The condition of the air cleaner filter is monitored by the
Engine Control Module. The “SERVICE AIR FILTER” message
will display in the Electronic Vehicle Information
Center (EVIC) when service is required. Refer to “Electronic
Vehicle Information Center (EVIC)” in “Understanding
Your Instrument Panel” for further information.
The “SERVICE AIR FILTER” message could be displayed
periodically. This is because engine air flow requirements
change based on driving conditions. As the filter becomes
more restrictive and air flow requirements increase the
“SERVICE AIR FILTER” message will be displayed. The
message may not be displayed in subsequent drive cycles
if the same conditions are not met. The air filter element
should be replaced within 250 miles (402 km) from the
first time this message is displayed to ensure proper
engine operation during all driving conditions.
Meanwhile, don't forget to lube the centering bearing of the double cardan (constant velocity) joint in the front axle driveshaft of a 4x4 every 7500 miles. It can be accessed with a hand greasse gun fitted with a needle attachment, without removing the shaft, skid plate, or anything else. While the manual says to grease the tie rod ends, my Ram doesn't have grease fittings there.