Avehicle fails an hc emission test at idle and 2,500 rpm, and the engine has an acceleration stumble. the heated oxygen sensor (ho2s) voltage is 0.1–0.3 volts on a scan tool, and the injector pulse width is high. no diagnostic trouble codes (dtcs) are found. when propane is directed into the air intake, ho2s voltage immediately increases and the injector pulse width decreases. the most likely cause of this problem is? a. a defective powertrain control module (pcm). b. a defective o2 sensor. c. an opening in the o2 sensor signal wire. d. low fuel-pump pressure.