Code 27, Sub-Oxygen Sensor Open Or Shorted Circuit VIN 5-CALIF. Only): Notes

The ECM supplies a voltage of .45 volt between terminals OX2 and OX1. If reading is taken with a 10-megohm DVOM, reading may be as low as .32 volt. When the sub-oxygen sensor reaches operating temperature, it produces a varying voltage from about .1-.9 volt.

The sub-oxygen sensor produces no voltage when it is less than 600°F (316°F). An open sensor circuit, or cold sensor, causes Open Loop operation.

1. A Code 27 will set when engine is at normal operating temperature, running for at least 2 minutes, O2 sensor voltage is not varying and above conditions are met for about 60 seconds.
2. This determines if sub-O2 sensor is the problem or if the ECM and wiring are the problem.
3. This checks continuity of White and Black wires from ECM. If Black wire is open, the ECM voltage on the White wire will be greater than .6 volt (600 mV).