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EPA desk statement on DEF sensor problems

Recently, fleets across the country, including some MTAC members, have experienced problems with malfunctioning Diesel Exhaust Fluid (DEF) sensors. Sensors in the DEF tanks are indicating that the truck is out of DEF, or that the quality of DEF in the tank is poor, even though neither of those things are true. The sensors are simply broken. When this happens, the trucks are physically incapable of being driven. In theory, the solution to this problem is to have new DEF sensors installed to replace the malfunctioning devices. However, due to the global chip shortage, that is not possible right now. Accordingly, the US EPA has issued a “Desk Statement” in which they state that truck manufacturers and their dealers are allowed to implement a “software solution” as a workaround, so that the trucks can be driven until the chip shortage situation is resolved. The desk statement from EPA is below:

EPA and the California Air Resources Board (CARB) have been working with the manufacturers of diesel vehicles and engines to address an issue related to the ongoing shortage of computer chips and the impact that has had on the availability of certain replacement parts. One part in particular, a sensor that monitors the quality of diesel emissions fluid (DEF), has been of concern because the failure of the part can lead to the vehicle being unable to operate. The Engine Manufacturers Association (EMA) on behalf of its member companies has proposed an industry wide approach that would provide a software solution for vehicles with failed parts to enable them to operate temporarily while the industry works to produce more replacement parts and that, long term, would provide replacement parts through a recall program. EPA and CARB have reviewed the proposed approach and believe it is appropriate for the companies to implement the proposed solution going forward as quickly as possible.

The manufacturers must still develop new software code and test it to ensure the software can be installed on vehicles in the field. The companies expect that they will be able to begin fixing some vehicles with failed sensors as soon as this week. The companies will also make available a similar software update for vehicles whose sensors have not failed but are among a group of vehicles where such a failure could be expected to occur to prevent a sensor failure from disabling the vehicle. This updated software is likewise expected to be available to service centers in the coming weeks.


Communications Team
Office of Transportation and Air Quality
U.S. Environmental Protection Agency