Main Oxygen Sensor (Federal Models)

Data Trouble Code No. 28 - Main Oxygen Sensor Signal

Detecting Condition

Open or Short in heater circuit of Main Oxygen Sensor (rear) for 0.5 seconds or more.
or
Main 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 Oxygen sensor (rear) signal voltage: alternating above and below 0.45 volts.

Trouble Area

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

Malfunction Indicator Lamp

Normal Mode On
Test Mode On