Diesel Engine Fluid (DEF) Sensor Simulator - Background Information and Assembly Instructions
DEF systems in modern diesel engines are crucial to reducing Nitrous Oxide (NOx) emissions and protecting the environment. The DEF system combines software, hardware, and DEF fluid that enable this critical task. Unfortunately, a flood of failures has recently affected one of the elements of the DEF system called the DEF sensor. The origins of this “DEF pandemic” are unknown, but the failures may be related to heat, poor design, or a high failure rate of the internal semiconductor.
The reason doesn’t matter, as the consequences of DEF sensor failure to the driver and passengers are significant. First, this failure causes an instant and progressive slowing of the engine function called “derate,” even though the primary process of the emissions systems continues to operate. Derate strands of vehicles and their occupants on the side of the road, or worse, force them to go slower than traffic, which is equally dangerous.
Replacement parts are not readily available. Covid-19 disruptions in the supply chain for semiconductors have exacerbated the availability problem. As of the fall of 2020, industry analysts forecast this chip shortage to last into 2022. As a result, many diesel equipment users are sidelined for days, weeks, or months while waiting for replacement parts. The irony is that despite the danger and the inconvenience, the affected emissions system is not broken. Instead, the DEF sensor stops reporting accurate information, so the ECM (Electronic Control Module) makes an incorrect assumption that the emissions system is broken and begins to derate the user. The classic symptom of the failed sensors is a Check Engine light (and possibly other indicators) with three fault codes followed by derate. Click here for details on the fault codes. Being unnecessarily derated in a diesel-powered vehicle is dangerous to its occupants.
DEF Head Alternatives Are Coming
Federally mandated DEF (Diesel Exhaust Fluid) monitoring systems have been stranding RVers. It’s a problem with plenty of dynamics, including why the sensors fail, a shortage of microchips, and rounding out with recalcitrant industry and government officials. In any event, we have stacks of emails from upset RVers who cannot or are afraid to use their rigs because of the issue. But thanks to persistent and innovative RVers, two DEF head alternatives are on the horizon. Read more...
DEF Sensor Workaround
If you’ve been following the saga of stranded RVers, it reads like a Shakespeare tragedy. But unlike the outcomes for Cleopatra or Macbeth, some of you may find light at the end of the story. In two months, a group of intrepid, like-minded, never-say-die RVers has devised a solution that may get their RVs on the road again. From all appearances, it’s a great DEF sensor workaround. Read more...
About the DEF Sensor Simulator
The DEF System Simulator (DSS) is a hardware/software solution a user can build. It is made of inexpensive, readily available parts to assist derated users in being able to perform a temporary fix as soon as a DEF sensor failure occurs and safely operate their vehicle until a repair can be obtained. Upon installation, the DSS removes (and follows a set of procedures contained in the documentation) the derate condition and will permit its users to reach a repair facility safely with full engine power. Read more...
DEF Sensor Simulator - Quick Build
Since the original DSS solution was published in September of 2021, the team has been looking at alternative hardware and software options. This page briefly describes and links to the build instructions for all the variants developed to date. The team has deemed the solution in the Recommended section to be the most viable current option considering factors such as price, size, parts availability, ease of programming, etc. Any build options are still possible solutions and provide opportunities during supply chain shortages. Read more...
DEF Sensor Emulator Firmware and Assembly Manual
This repository contains the compiled Arduino Due sketch for emulating a Diesel Exhaust Fluid (DEF) head and instructions for assembling an emulator. This code is compiled for the Arduino DUE, UNO and ATMega2560. Read more...
Arduino Due with Dual CAN Bus Interface (Original Build)
The original project uses an Arduino DUE board with a separate CAN board add-on. Programming the board is not difficult but somewhat more complex than the RP2040 and requires a Windows system. However, it does not require any soldering.