DTC 27 (CALIF Emissions) Sub-Heated O2 Sensor (Sub-Ho2S), Open Or Shorted Circuit: Notes
WARNING: This page is about a different variant/trim than selected.
NOTE:
PCM activates HO2S heater to promote quick operation of O2S during engine warm-up to improve fuel control. See SYSTEM/COMPONENT TESTS - 1.8L
article.
When Sub-Heated Oxygen Sensor (sub-HO2S) 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-HO2S input at PCM 0.45 volt or less.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Checks for faulty sub-HO2S.
- Checks for an open in Black wire between PCM and sub-HO2S.
- Checks for an open in Brown wire between PCM and G106.
- Checks for short to ground in Black wire between PCM and sub-HO2S, open in Brown wire to sub-HO2S, and a faulty PCM.