Code 27 (Calif.)

Condition is one of the following:

• Open or short in heater circuit of sub-heated oxygen sensor for more than 0.5 second. Probable cause: open or short in heater circuit of sub-heated oxygen sensor, defective sub -heated oxygen sensor or defective oxygen sensor.
• Main oxygen sensor signal is more than 0.5 volt and sub -oxygen sensor signal is less than 0.5 volt with engine temperature more than 176°F (80°C), engine speed more than 1500 RPM and accelerator pedal fully depressed for 2 seconds. Probable cause: open or short in heater circuit of sub-heated oxygen sensor, defective sub-heated oxygen sensor or defective ECM.