15.4 Heater noise couplings
Heater noise couplings into the rear oxygen sensor's signal are detectable only when the heater is being switched off (falling edge). A heater-off-counter is incremented every time the rear oxygen sensor's heater is switched off. Likewise a coupling-detection-counter is incremented when the switching off of the heater is accompanied by a rear oxygen sensor voltage gradient that exceeds a calibrated threshold for a calibrated period of time. If the heater-off-counter reaches a calibrated threshold and at the same time the coupling-detection-counter exceeds a calibrated threshold, a LSHnpl fault will be set.