Main Oxygen Sensor (Federal Models)

Data Trouble Code No. 21 - Main Oxygen Sensor (front) Signal

Detecting Condition

Main Oxygen Sensor (front) voltage is reduced to between 0.35 volts and 0.70 volts for 90 seconds under the following conditions (2 trip detection):

- Engine Coolant Temperature between 80°C (176°F) and 95°C (203°F).
- Engine Speed 1,500 rpm or more.
- Load driving i.e., transmission in overdrive, air conditioning on, 80 km/h (50 mph).
- Main Oxygen Sensor (front) voltage alternating above and below 0.45 volts.

Trouble Area

- Main Oxygen Sensor (front) circuit.
- Main Oxygen Sensor (front).

Malfunction Indicator Lamp

Normal Mode On
Test Mode On