The code eliminaters are basically "dummy" modules that plug-in in place of sensors to eliminate getting fault codes/ SES lights.
The two generally available that I'm aware of, are for the exhaust back pressure sensor and fit the exhaust back pressure vale (EBPV) in the turbo pedestal.
Usually sooner or later, the exhaust back pressure sensor tube will plug up with carbon/soot or will develope a hole in the tube. By unplugging the wire connector from the sensor and installing the code eliminator, you will prevent false fault codes if the tube gets plugged. I removed the tube altogether, plugged the hole in the exhaust manifold with a steel pipe thread plug and installed a code eliminator.
The code elimator for the EBPV comes in handy if you want to do away with the EBPV or need to replace your turbo pedestal and want to replace it with a cheaper pedestal without the EBPV actuator.