Code 13, O2 Sensor CKT/Open CKT

ECM supplies a voltage of approximately .45 volt between ECM terminal Y19 and ground. If voltage is measured with a high-impedance, 10-megohm DVOM, reading may be as low as .32 volt. The O2 sensor varies the voltage within a range of approximately .1 volt (lean exhaust) to 1 volt (rich exhaust). The O2 sensor is similar to an open circuit and produces no voltage when sensor temperature is less than 600°F (316°C). A cold sensor, or open circuit, causes open loop condition.

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

Before using 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 ignition timing and engine compression. Check for vacuum leaks. If Code 13 is present with another code, the later code has priority.

If the following conditions are present for at least 30 seconds, Code 13 will be set.
- Engine is at normal operating temperature.
- Engine has been running for at least 2 minutes after engine start.
- O2 signal voltage is steady between .35-.45 volts.
Checks if problem is a faulty O2 sensor, or faulty ECM and wiring. Perform this test using a high-impedance, 10-megohm DVOM.