DTC 27 (CALIF Emissions), Sub-O2 Sensor (Sub-O2S), Open Or Shorted CKT: Notes

When sub-oxygen sensor (sub-O2S) reaches operating temperature, it produces a varying voltage. Voltage will vary from 0.1 volt (exhaust is lean) to 1.0 volt (exhaust is rich). ECM monitors voltage and determines concentration of gases in exhaust after catalytic converter. ECM uses this input along with Oxygen sensor (O2S) input to adjust fuel to maintain optimum air/fuel ratio. DTC 27 will set when engine is at operating temperature and engine is off idle for 2 seconds or more with O2S input at ECM 0.45 volt or more, and sub-O2S input at ECM 0.45 volt or less.

1. Checks for a faulty sub-O2S.
2. Checks for an open in Black wire between ECM and sub-O2S.
3. Checks for an open in Brown wire between ECM and G106.
4. Checks for a short to ground in Black wire between ECM and sub-O2S, an open in Brown wire to sub-O2S, and a faulty ECM.