Code 13, Open Oxygen Sensor Circuit: Notes

The ECM supplies a voltage of about .45 volt between terminals D7 and D6. If measured with 10-megohm voltmeter, voltage reading may be as low as .32 volt.

Oxygen sensor varies voltage within range of approximately .1 volt (lean exhaust) to 1 volt (rich exhaust). The sensor is like an open circuit and produces no voltage when sensor temperature is less than 600°F (316°C). An open sensor circuit or cold sensor causes open loop operation.

1. Code 13 will set if the following conditions occur:
   • Code 21 or 22 is not being detected.
   • Engine is at normal operating temperature.
   • There is at least 40 seconds of engine run time.
   • Oxygen signal is steady between .35-.55 volt.
   • Throttle angle is more than 7 percent.
   • All conditions are met for one minute.

If conditions for Code 13 exist, system will not go to closed loop operation.

1. This test determines whether the oxygen sensor is the problem, or the ECM and wiring are at fault.
2. When performing this test, use only a high impedance digital volt-ohmmeter. This test checks the continuity of circuits No. 412 and No. 413. If circuit No. 413 is open, ECM voltage on circuit No. 412 will measure greater than .6 volt.