Post Bill C-2 we were able to use this "defence", really a negation of the presumption, if we were able to connect that malfunction with the reliability of the measurement result. That "defence" is gone now. Malfunctioning instruments result in conclusive proof, unless we can mount a constitutional challenge. Under Bill C-2, defence lawyers and judges had a lot of trouble with the concept of "malfunction". What is it? It is not just an error message. It should relate to the "function" of an approved instrument, namely to give a reliable QUANTIFICATION of the measurand, blood alcohol concentration, at time of use. Take a close look at the analysis in St-Onge Lamoureux and attempt to understand what "reliability" means in that judgment. I think poor calibration or lack of evidence of good calibration or re-calibration will result in a malfunction. I think poor use of standard operating procedures (individual or systemic) result in malfunction or operator error. Unique body or ambient presentations can result in malfunction (see body temperature in case referred to in St-Onge).