Code 27, Sub-Oxygen Sensor CKT, Open Or Shorted CKT (CALIF.): Notes

When sub-oxygen sensor reaches operating temperature, it varies a voltage between .1-.9 volt.

The O2 sensor will not produce voltage until sensor reaches 600°F (316°C). When sensor is less than this temperature, an open loop condition exists.

1. This step checks for a poor connection or for a faulty ECM. Code 27 will set under the following conditions:
   • Engine at normal operating temperature.
   • At least 2 minutes have elapsed since engine start-up.
   • O2 signal voltage is steady between zero or one volt.
   • All the above conditions are met for about 60 seconds.
2. This checks for an open circuit in White, Black or Brown wire to ECM.
3. This determines if sub-oxygen sensor is the problem, or if ECM and wiring is at fault.