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, 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 the exhaust is lean. 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.

Test Number 1)  Code 13 will set if the following conditions occur:

• Code 21 or 22 is not being detected.
• Engine at normal operating temperature.
• At least 40 seconds engine run time.
• Oxygen signal steady between .35-.55 volt.
• Throttle angle more than 7 percent.
• All conditions must be met for 3 seconds.
• If conditions for Code 13 exist, system will not go to closed loop operation.

Test Number 2)  This test determines if the oxygen sensor is the problem, or if the ECM or wiring is at fault.

Test Number 3)  When performing this test, use only a high impedance 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 measure greater than .6 volt.