Code 13 - Open Oxygen (O2) Sensor Circuit
The ECM supplies voltage of about .45 volt between terminals D7 and D6. (If measured with a 10-megohm digital voltmeter, this may read as low as .32 volts.) The oxygen sensor varies the voltage within a range of about one volt (rich exhaust) to .1 volt (lean exhaust). The oxygen sensor is like an open circuit and produces no voltage when it is below about 600°F (316°C). An open sensor circuit or cold sensor causes open loop operation.
This engine is equipped with an electrically heated oxygen sensor. The sensor is energized by the fuel pump relay, and remains on as long as the engine is running. Failure of the heating element, battery feed or ground circuits may cause Code 13 to be set at idle or low RPM.
Code 13 will set at least 2 minutes after engine start if oxygen sensor signal voltage is steady and between .35 and .55 volts for more than one minute or if throttle position is off idle about 1200 RPM.
- Grounding diagnostic terminal with engine running activates "Field Service Mode". This allows the ECM to confirm either open or closed loop operation using the "SERVICE ENGINE SOON" light.
- This step verifies that no additional codes are stored, and that Code 13 is intermittent.
- This step simulates a lean exhaust. If ECM and wiring are okay, the ECM will see the lean condition and turn the "SERVICE ENGINE SOON" light off for at least 30 seconds after engine start, and then flash "open loop". It is considered normal if light remains off for a longer period of time before flashing open loop.