How do I handle DEF system issues in my diesel Tiffin (e.g. “Check Engine” derate due to DEF sensor failures)?

Fill the DEF tank completely full of diesel exhaust fluid in order to correct any fault conditions.

A flashing DEF lamp combined with an illuminated WARNING or CHECK ENGINE lamp indicates that the DEF level has fallen below the initial derate level.

The engine power will be limited automatically.

This can be corrected by filling the DEF tank with diesel exhaust fluid.

If the engine has been shut down, idled for 1 hour, or if fuel has been added after the DEF tank has been emptied, the STOP ENGINE lamp will also be illuminated along with the flashing DEF lamp and illuminated CHECK ENGINE lamp.

The engine vehicle speed will also be limited to 5 mph.

In order to remove the 5 mph speed limit, the diesel exhaust fluid tank must be filled to at least 10 percent volume of the tank.