YES, I have had the check engine light come on which turned out to be the DEF temp indicator. Here's how I found out.
We were traveling through Michigan in June, having a wonderful time. The check engine light came on. I called Tiffin and they walked me through checking various codes on the dash LED instruments. They tentatively diagnosed the problem as the DEF temp indicator. Here's the scary part - they told me that the engine would continue to operate routinely for "about 80 miles" then I would experience a loss of power and, eventually would be slowed to a crawl at which point I would need a tow. We were about 45 miles from the nearest Freightliner dealer in Traverse City, MI. I called them and explained the problem and they told me to head their way. We made it OK after a bit of a nervous ride.
They had not seen that problem before but contacted Freightliner. They sent the part overnight and we were on the road late the next day. The repair took so long because they had to drop the DEF tank to replace the sensor, which is located at the top of the tank. The part was under warranty (2013 Allegro RED) so there was no cost to us. We stayed in the Traverse City lot overnight using their 50 amp hook up.
Just another day enjoying the RV life