DTC 27 (Federal Emissions) Sub-O2 Sensor (Sub-O2S), Open Or Shorted Circuit: 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). PCM monitors voltage and determines concentration of gases in exhaust after catalytic converter. PCM 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 PCM 0.45 volt or more, and sub-O2S input at PCM 0.45 volt or less.

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