It wasn’t even a week after the truck went in for service that I started getting the “Exhaust Fluid Range” notifications. At first, they were fairly friendly. When I started the truck, I saw “Exhaust Fluid Range 298 Miles” where the trip odometer and regular odometer usually were. I could push the check-mark button in the driver information center and get the trip info again, but the DEF range would automatically be displayed every time I restarted the truck. That was OK with me, as it was more important to know that than the fuel range — there’s a regular gauge for that, of course, and there isn’t one for the diesel exhaust fluid. We’ve heard that there may be some sort of gauge update for the DEF in the near future.

So, as the range went down (in case you’re wondering, it seems to go down faster than the number of miles traveled) it became more important that I buy DEF. The tank holds 5.3 gallons or so, so I bought two 2.5-gallon containers of the stuff at O’Reilly. Less than 20 bucks for something you’ll refill every 7500 or so miles? That’s not bad. (However, the local Chevy dealer charges about $15 for just one gallon, so if you’re okay with filling the tank yourself and buying it at an auto parts store, you’ll save lots of money.) I left the containers at work, expecting I had a little time before I’d have to add the fluid. It also turns out that the range gauge is either very conservative or wildly inaccurate. As I was exiting the freeway on an off-ramp that angled downhill, the exhaust fluid range went from a reasonable 190 miles to a display that read “Exhaust Fluid Low” and “Speed Limited Soon.” Well, that’s when I got curious. What would happen next? It didn’t take too long for the display to change to “55 MPH Max Speed Upon Restart,” alternating between that and “Exhaust Fluid Empty Refill Now,” with a flashing light on the display and an occasional chime. For those who were concerned that there wouldn’t be enough warning before the truck ran low on fluid, there’s nothing to worry about. It lets you know what’s going on and does it often.

Sure enough, when I stopped the truck and restarted it, the speed was limited to 55 mph. According to the guide that GM sent us, the speed limiter will kick in at lower speeds as time goes on, and I suppose I could’ve gone further to see how slow the truck would make me drive, but I’d had enough fun not being able to go faster than 55 mph, so it was time to refill the tank.

Of the two trucks on the market to have DEF fillers, this was the less convenient of the two. Ford’s is located next to the fuel filler on the side of the truck, behind the same fuel door. In the Silverado, it’s on the passenger side in the engine bay, near the firewall. And, as I am 5’8″, I needed an extra boost to reach it. If you own a Silverado HD and have to refill the DEF tank, I’d recommend that if you aren’t 6’3″ or so, use a stepstool or park near a curb that you can stand on. It isn’t hard to fill, but the filler location makes it a little awkward. Once the tank was full and I was back on the road, it took longer than I thought for everything to return to normal. But after about 20 minutes, the truck was no longer speed-limited and the flashing light and chime stopped.