Patent ID: 8607625

Claim:
A service device operable to test the SCR device of an exhaust gas treatment system of an internal combustion engine comprising: a controller that includes sub modules containing logic that receive various inputs from the engine, the exhaust system and an engine controller; a first sub module that determines an operational status of a NOx sensor that is upstream and a NOx sensor that is downstream of the SCR device, wherein the operational status comprises at least one of an on/off operational status and a hi/low operational status, a second sub module that determines the on/off status a NH 3 injector upstream of the SCR device, such that when the first sub module indicates at that both upstream and downstream NOx sensors are on and simultaneously that NH 3 injector is on the second sub module is configured to issue a signal to the NH 3 injector to turn off; a validation module that monitors the engine until enough upstream NOx mass has been generated by the engine, based on engine operating parameters (combustion air in, fuel, temperature,) to deplete and NH 3 load remaining in the SCR device and once the appropriate NOx mass has passed through the SCR device to deplete the NH 3 load, the validation module is configured to determine the operational status of the NOx sensors as follows: if 1−downstream NOx ppm/upstream NOx ppm=approx. 0; then the downstream NOx sensor is reading the same as the upstream NOx sensor and the downstream NOx sensor is determined to be good and the SCR device may have to be investigated for possible failure and replacement; and if 1−downstream NOx ppm/upstream NOx ppm>approx. 0; then the downstream NOx sensor is reading high and the downstream NOx sensor is determined to be bad and NOx sensor may have to be investigated for possible failure and replacement.