Oxygen Sensor Testing

H02S Test Chart:

H02S Oxygen Sensor Circuit:

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, the exhaust is lean, and if the voltage input is about .9 volt, 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. Code 13 will set if the following conditions are met for about 30 seconds:

^ Engine operating temperature greater than 70°C (158°F).
^ At least 2 minutes engine run time after start.
^ Engine speed greater than or equal to 260 rpm.
^ Oxygen sensor temperature below 360°C (600°F).
^ MAP greater than 350 mm (Hg).

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

1. This checks for a short to voltage in YEL/BLU wire or for a faulty ECM.

2. This checks for a short to ground in YEL/BLU wire, a faulty ECM or for a faulty (H02S).

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."