Main Heated Oxygen Sensor (California Models)

Data Trouble Code No. 28 - Main Heated Oxygen Sensor Signal

Detecting Condition
(A) Open or short in heater circuit of main heated oxygen sensor (rear) for 0.5 seconds or more.
or
(B) Main heated oxygen sensor (rear) signal 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 (ex. A/T in overdrive or M/T in 5th gear, A/C on, flat road, 50 mph)
- Main heated oxygen sensor (rear) signal voltage: alternating above and below 0.45 volts.

Trouble Area
(A) ^ Open or short in heater circuit of main heated oxygen sensor (rear).
^ Main heated oxygen sensor (rear) heater.
^ Engine Control Module.
or
(B) ^ Main heated oxygen sensor (rear) circuit.
^ Main Heated Oxygen Sensor (rear).

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