Code 21 - Main Oxygen Sensor Signal

Data Trouble Code No. 21 - (Main)[1] Oxygen Sensor Signal

Detecting Condition
(Main)[1] oxygen sensor voltage is reduced to between 0.35 volts and 0.70 volts for 60 seconds under the following conditions:

NOTE: (2 trip detection logic)
See Description of 2 Trip Detection Logic under "Trouble Code Descriptions".
Diagnostic Trouble Code Descriptions

^ Engine coolant temperature 80°C (176°F) or more.
^ Engine speed 1,500 rpm or more.
^ Load driving i.e., transmission in overdrive or fifth gear, air conditioning on, 50 mph (80 km/h).
^ (Main)[1] oxygen sensor voltage alternating above and below 0.45 volts.

Trouble Area
^ (Main)[1] oxygen sensor circuit.
^ (Main)[1] oxygen sensor.

Malfunction Indicator Lamp
Normal Mode ON
Test Mode ON

[1] "Main" is for California specification vehicles ONLY.
(non-California models have only 1 oxygen sensor)