Code 13 - Open Oxygen Sensor Circuit: Notes

The ECM supplies a voltage of about .45 volt between circuits No. 412 and 413. If measured with a 10-megohm digital voltmeter, this may read as low as .32 volt. The oxygen sensor varies the voltage within a range of about one volt if the exhaust is rich, down to about .10 volt if exhaust is lean. The sensor is like an open circuit and produces no voltage when it is less than 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

1. Code 13 will set when the following conditions occur:
   • Engine at normal operating on temperature.
   • At least 2 minutes elapsed since start-up.
   • Oxygen signal voltage steady between .35 and .55 volt.
   • Throttle angle greater than 5 percent (about .3 volt greater than closed throttle voltage).
   • All conditions must be met for about 60 seconds. If conditions for a Code 13 exist, the system will not go "closed loop".
2. This test will determine if the sensor, wiring or ECM is the cause of Code 13.
3. When conducting this test, use only a high impedance (10-megohm) digital volt/ohmmeter. This test checks the continuity of circuits No. 412 and 413. If circuit No. 413 is open the ECM voltage on circuit No. 412 will be greater than .6 volt.