Code 13, Open Oxygen Sensor Circuit: Notes

The ECM supplies a voltage of about .45 volts between terminals No. E14 and E15 (No. B2 and B23). If measured with a 10-megaohm digital voltmeter, this may read as low as .32 volts.

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 below 600°F (360°C). An open sensor circuit, or cold sensor causes "open loop" operation.

1. Code 13 will set if the following conditions occur:
   • Engine at normal operating temperature.
   • At least one minute engine time after start.
   • Oxygen signal voltage steady between .35-.55 volts.
   • Throttle angle more than 7 percent.
   • All conditions must be met for about 20 seconds.

If conditions for a Code 13 exist, the system will not go into "closed loop".

1. This test determines if the oxygen sensor is the problem, or if the ECM and wiring are at fault.
2. When doing 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 be greater than .6 volts (600 mV).