Heated Oxygen Sensor (HO2S) #21 Connector end view (C172)

Fig 1: Heated Oxygen Sensor (Ho2S) #21 Connector End View (C172)

Courtesy of FORD MOTOR CO.

Pin	Circuit	Circuit function
1	391 (RD/YE)	Voltage supplied in Start and Run (overload protected)
	361 (RD)	Voltage supplied in Start and Run (overload protected)... Natural Gas Vehicle (NGV)
2	388 (YE/LB)	Heated Oxygen Sensor (HO2S) #21 (9F472), heater
3	359 (GY/RD)	signal, return
4	94 (RD/BK)	Heated Oxygen Sensor (HO2S) #21 (9F472), input