Main Heated Oxygen Sensor (California Models)

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

Detecting Condition

Open or Short in heater circuit of Main Heated Oxygen Sensor (rear) for 0.5 seconds or more.
or
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 (Trans in over drive, A/C on, flat road, 50 mph)
- Main Heated Oxygen sensor (rear) signal voltage: alternating above and below 0.45 volts.

Trouble Area

- Open or short in heater circuit of Main Heated Oxygen Sensor (rear).
- Main Heated Oxygen Sensor (rear) heater.
- Engine Control Module.
or
- Main Heated Oxygen Sensor (rear) circuit.
- Main Heated Oxygen Sensor (rear).

Malfunction Indicator Lamp

Normal Mode On
Test Mode On