Code 21 - Main Oxygen Sensor Signal - Front

Data Trouble Code No.21 - Main Heated Oxygen Sensor Signal

Detecting Condition
(A) Open or short in heater circuit for the main heated oxygen sensor (front) for 0.5 seconds or more
or
(B) Main heated oxygen sensor (front) voltage is reduced to between 0.35 volts and 0.70 volts for 60 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 (A/T) or 5th gear (M/T), air conditioning on, flat road, 80 km/h (50 mph)].
- Main heated oxygen sensor (front) voltage alternating above and below 0.45 volts.

Trouble Area
(A) ^ Open or short in heater circuit of main heated oxygen sensor (front).
^ Main heated oxygen sensor (front).
^ ECM
or
(B) ^ Main heated oxygen sensor (front), or it's circuit.

Malfunction Indicator Lamp
(A) Normal Mode On
Test Mode N.A.
or
(B) Normal Mode On
Test Mode On

Recorded in memory?
Yes