Code 13, Open Oxygen Sensor Circuit (4.3L Turbo): Notes

When exhaust temperature is less than 600°F (316°C), the O2 sensor is open and produces no voltage. An open sensor circuit or cold sensor will not all system to entire closed loop.

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

Code 13 will set at normal operating temperature if at least 2 minutes have passed since engine start, O2 signal voltage is steady between .35-.55 volt and throttle position sensor signal is above idle. All conditions must be met for at least 1 minute.
This checks the oxygen sensor heating element. Resistance should be 3.5-14 ohms at 662°F (350°C).
This determines if fault is in O2 sensor, ECM or wiring.
Use only a high-impedance Digital Volt-Ohmmeter (DVOM) while checking for continuity in signal and ground circuits. If ground circuit is open, voltage on signal circuit will be greater than .6 volt.
If the A/C fuse is blown, check the A/C control circuit or generator for short circuits.