Code 13, Oxygen Sensor Circuit Open Circuit

ECM supplies a voltage of approximately .45 volt between terminal "Y19" and ground. If reading is taken with a 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor varies the voltage within a range of approximately one volt, if exhaust is rich, to approximately .10 volt, if exhaust is lean. The O2 sensor is similar to an open circuit and produces no voltage when sensor temperature is less than 600°F (316°C). An open circuit or cold sensor causes an "Open Loop" condition.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Before using trouble shooting chart to diagnose this code, ensure the following components are in good condition; air cleaner, spark plugs, high tension wires, distributor cap and rotor. Also check for vacuum leaks, ignition timing and engine compression. If Code 13 and another code are given together, the later code has priority.

If the following conditions are met, this will set a Code 13:
- Engine at normal operating temperature.
- Engine running at least 2 minutes after engine start.
- O2 signal voltage steady between .35-.55 volts.
- All conditions must be present for at least 30 seconds.
This checks if O2 sensor is the problem or if ECM and wiring are faulty. When doing this test, use only a high impedance DVOM. This test checks the continuity of circuits No. 412 and 413. If circuit No. 413 is open, ECM voltage on circuit No. 412 will be over .5 volts.