Oxygen Sensor Circuit (Open Circuit)

Circuit Description

The ECM supplies a voltage of about 0.45 volt between terminals "D7" and "D6". (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts.) The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down through about 0.10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below 360 degrees Celsius (600 F). An open sensor circuit or cold sensor causes "Open Loop" operation.

Problem Description:

Code 13 will set:

Engine at normal operating temperature.
At least 2 minutes engine time after start.
O2 signal voltage steady between 0.35 and 0.55 volts.
RPM above 1600
Throttle position sensor signal above 12% (about 0.5 volts above closed throttle voltage).

All conditions must be met for about 20 seconds. If the conditions for a Code 13 exist the system will not go "Closed Loop".

Diagnostic Aids:

Normal "Scan" voltage varies between 100 mV to 999mV (0.1 and 1.0 vols) while in "Closed Loop". Code 13 sets in 1 minute if voltage remains between 0.35 and 0.55 volts, but the system will go "Open Loop" in about 15 seconds.

"Scan" Diagnostics:

Engine at normal operating temperature (above 80 degrees C).

Run engine above 1200 rpm for two minutes.

Does scantool indicate "Closed Loop"?

YES