Code 13, Open Oxygen Sensor Circuit: Notes

The ECM supplies a voltage of about .45 volt between terminals D7 and D6. If measured with 10-megohm voltmeter, this may read as low as .32 volt.

The oxygen sensor varies the voltage within a range of about one volt, if the exhaust is rich, down to about .10 volt if the exhaust is lean. The sensor is like an open circuit and produces no voltage when below 600°F (316°C). An open sensor circuit or cold sensor causes "open loop" operation.

1. Code 13 will set if the following conditions occur:
   • Fuel volume okay but pressure too low. System will run lean and may set a Code 44. Hard starting and poor performance.
   • Check for restriction in fuel flow. Normally a vehicle with less than 9 psi fuel pressure at idle will not be driveable. However, if the pressure drop occurs only when driving, the engine will surge and then stop as pressure drops to zero.
   • Code 21 or 22 is not being detected.
   • Engine at normal operating temperature.
   • At least 40 seconds engine run time.
   • Oxygen signal steady between .35-.55 volt.
   • Throttle angle more than 7 percent.
   • All conditions must be met for 3 seconds.
2. This test determines if the oxygen sensor is the problem, or if the ECM or wiring is at fault.
3. When performing 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 measure over .6 volt.