DTC 21 (CALIF Emissions) O2 Sensor Circuit, Open Or Shorted Circuit: Notes
WARNING: This page is about a different variant/trim than selected.
NOTE:
For DTC 21 (Federal Emissions) see DTC 21 (FEDERAL EMISSIONS) chart.
When Oxygen Sensor (O2S) reaches operating temperature, it produces a varying voltage between 0.1 volt (exhaust is lean) to 1.0 volt (exhaust is rich). PCM monitors voltage and determines concentration of gases in exhaust and adjusts fuel to maintain optimum air/fuel ratio. DTC 21 will set if O2S input voltage at PCM is 0.35-0.70 volt for 60 seconds or more with engine speed greater than 1500 RPM, and engine coolant temperature is greater than 176°F (80°C).
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Checks for faulty O2S.
- Checks for an open in Black wire between PCM and O2S.
- Checks for an open in Brown wire between PCM and G106.
- Checks for a short to ground in Black wire between PCM and O2S, an open in Brown wire to O2S, and a faulty PCM.