DTC 21

Fig. 15 Diagnostic Code 21 & 28 (Main Oxygen Sensor & Heater Signal, Part 1 Of 5):

Fig. 15 Diagnostic Code 21 & 28 (Main Oxygen Sensor & Heater Signal, Part 2 Of 5):

Fig. 15 Diagnostic Code 21 & 28 (Main Oxygen Sensor & Heater Signal, Part 3 Of 5):