Sub-Oxygen Sensor - California

Sub-Oxygen Sensor Circuit:

Sub-Oxygen Sensor Testing:

CIRCUIT DESCRIPTION:

The oxygen sensor (02S), produces a voltage that varies between .1 volt and .9 volt under normal operating conditions. The ECM monitors this voltage and determines if the exhaust is lean or rich. If the voltage input at the ECM is about .1 volt, the exhaust is lean, and if the voltage input is about .9 volt, the exhaust is rich. If the (O2S) is below 360°C (600°F) it is like an open circuit and will not produce a voltage. This will cause "OPEN LOOP" operation.

Code 21 will set if:

^ Engine is warmed up.
^ Engine is off idle for 2 seconds or more.
^ O2S voltage is .45 V or more.
^ Sub-O2S voltage is .45 V or less.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This checks to see if the sub-O2S is faulty.

2. This checks for an open in BLK wire between sub-O2S and ECM.

3. This checks for an open in BRN wire between sub-O2S and G106.

4. This checks for a short to ground in BLK wire between sub-O2S and ECM, an open in BRN wire to the sub-O2S on federal emissions vehicles and for a faulty ECM.


DIAGNOSTIC AIDS:

Normal voltage on the (02S) input wire varies between 100 mV and 1000 mV (0.1 and 1.0 volt), while in "CLOSED LOOP."