Oxygen Sensor Testing

HO2S Heater Wiring:

HO2S Heater (Open Circuit) Diagnostic Chart:

CIRCUIT DESCRIPTION:

The heated oxygen sensor (H02S), 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, when the exhaust is lean, and if the voltage input is about .9 volt, when the exhaust is rich. The (H02S) has a built-in heater that keeps the (H02S) at normal operating temperature while the engine is running. If the (H02S) is below 360°C (600°F) it is like an open circuit and will not produce a voltage. This will cause "OPEN LOOP" operation.

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

1. Code 13 will set if:

^ Engine operating temperature greater than 69.5°C (183°F).
^ At least 2 minutes engine run time after start.
^ HO2S voltage steady between .347 V and .547 V.
^ Throttle angle above 5%.
^ Vehicle speed > 3 mph.
^ All conditions met for 40 seconds.

2. This test determines if the HO2S is the problem or if the ECM and wiring are at fault.

3. This checks the continuity of "D7" and "D6". If "D6" is open, the ECM voltage on "D7" will be over .6 volt (600 mV)


DIAGNOSTIC AIDS:

Normal voltage on the (H02S) input wire varies between 100 mV and 999 mV (0.1 and 1.0 volt), while in "CLOSED LOOP."