The Diesel Exhaust Fluid (DEF) tank may appear to be empty shortly after beginning a towing trip or it may be difficult to properly fill the DEF tank on some 2020-2025 Silverado 1500, Silverado 2500HD/3500HD, Tahoe, Suburban, Sierra 1500, Sierra 2500HD/3500HD, Yukon; and 2021-2025 Escalade models equipped with a diesel engine (RPO LM2, LZ0, L5P). Under high load towing conditions, the amount of DEF used may engage the DEF warning system before the DEF system can read the tank has been filled. If the tank is filled under these conditions, the DEF system will not see the fill and may not see subsequent fill attempts. (Fig. 5)
Fig. 5
The vehicle should be driven to allow the DEF warning system to progress until a specific speed limitation warning is displayed on the Driver Information Center before adding DEF to the tank. In the U.S., the speed limitation will be 65 mph (105 km/h).
TIP: Refer to Bulletin #22-NA-150 to verify the Reductant Control Module is has the latest update available and that the Reductant Fluid Tank Level has been reset.
The DEF level also can be exacerbated by vehicle loading that exceeds the Gross Combined Weight Rating (GCWR) when towing. Reference the towing label inside the driver’s door and, using a commercial scale, confirm that the total weight of the vehicle, trailer and cargo does not exceed the GCWR.
DEF Warning Strategy
When the DEF warning strategy is implemented, it is based on an estimated range to speed limitation of 1,000 miles (1,609 km). When the gauge is reviewed during the warning strategy, the gauge will show very little DEF or no DEF at all. This is a normal condition. The DEF system needs to complete the warning strategy (Fig. 6) and inducement is not shown on the gauge. Only the reserve level is displayed in some cases. With large trailers, there may not be a reserve and there will not be any gauge bars displayed.
Fig. 6
Do not immediately add DEF when there is a DEF system message and a low gauge reading in order to drive the gauge back up or to remove the DIC message. The following chart (Fig. 7) shows the DIC messages that may appear while towing and the messages in red where it is not appropriate to add DEF to the tank. Areas in green indicate that at these warning levels and when these messages are displayed it is OK to add DEF to the tank.
Fig. 7
Customers should be encouraged to not fill the DEF tank under these conditions until the warning strategy indicates a specific speed limitation will be reached (65mph/105 km/h). When the system message changes from “Speed Limited Soon” to “Speed Limited to 65mph in xx Miles” it is safe to add DEF and the fill will be detected. The messages may stop for a short period, but they will begin again shortly if the vehicle is still towing. The vehicle can continue to be operated until the DIC message is displayed that inducement and speed reduction are imminent. This is technically the best time to fill the DEF tank, and the system will register a fill at the inducement level if DEF has not been added during the warning strategy and there are not any functional issues with the DEF system.
TIP: When adding DEF to an empty or very low tank, always add at least 2 gallons (7.2 L) of DEF to release the vehicle from speed limitation.
Check out Bulletin #24-NA-196 for more information.
– Thanks to Dave MacGillis, Kevin Minor and Mike Waszczenko
