ECM offers three NOx Module Kits. The NOxCANt and NOxCANf Kits are recommended for spark ignition and diesel engine applications. The NOxCANg Kit has a more stable zero point and is therefore recommended for diesel and lean-burn combustion processes where the NOx level is less than 10 ppm.
The NOxCANt and the NOxCANg Kits have a cross-sensitivity to NH3. For the NOxCANt, the cross-sensitivity is 1:0 (1 ppm NH3 looks like 1 ppm NOx to the sensor). For the NOxCANg, the cross-sensitivity is approximately 1:0.67 (1 ppm NH3 looks like 0.67 ppm NOx).
The NOxCANf has a built-in and replaceable NH3 absorption filter. The NOxCANf has zero cross-sensitivity to NH3, however the exhaust gas temperature cannot exceed 210℃ and the filter will require replacement at intervals as short as 20 minutes.
An understanding of NH3 cross-sensitivity is important for tailpipe installations (as opposed to engine-out installations), since three-way catalytic converters produce NH3 when running stoichiometric and richer and diesel engines will inject urea into the exhaust which turns into NH3.