Code 13 - Open Oxygen (O2) Sensor Circuit

Code 13 will set with the engine operating temperature at least 2 minutes after engine start. The ECM must see: O2 signal voltage steady between .35 and .55 volts for more than 1 minute, or see TPS signal indicating not at idle. The ECM supplies a voltage of about .45 volt between terminals "D7" and "D8". (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volts). The O2 sensor varies the voltage within a range of about 1 volt if the exhaust is rich, down to about .10 volt if the exhaust is lean.

1. Grounding the diagnostic terminal with the engine running enables the "Field Service Mode", allowing the ECM to confirm either open or closed loop operation using the "SERVICE ENGINE SOON" light.
2. This step verifies no additional codes stored, and that Code 13 is intermittent. SEE TROUBLE SHOOTING charts in the CEC TESTS W/O CODES article in this section.
3. This step simulates a lean exhaust. If the ECM and wiring are okay, the ECM will see the lean condition and turn the "SERVICE ENGINE SOON" light off at least 30 seconds after engine start and then flash open loop. It is normal for the light to remain off for a longer period of time before flashing open loop.