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

Sub-oxygen (O2) sensor produces a varying voltage as engine reaches normal operating temperature. Voltage will vary from .1 (lean) to 1.0 (rich) volt. ECM monitors voltage and determines concentration of gases in exhaust after converter. ECM uses this input and Oxygen (O2) sensor input, and adjusts fuel to maintain air/fuel ratio. Code 27 will set when engine is at operating temperature and engine is off idle for 2 seconds or more with sensor input at ECM .45 volt or more, and sub-O2 sensor input at ECM .45 volt or less.

1. Checks for faulty sub-O2 sensor.
2. Checks for open in Black wire between ECM and sub-O2 sensor.
3. Checks for open in Brown wire between ECM and G106.
4. Checks for short to ground in Black wire between ECM and sub-O2 sensor, open in Brown wire to sub-O2 sensor, and a faulty ECM.