DTC 13

Code Chart 13:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The ECM supplies a voltage of about .45 volt between terminals "GE14" and "GE15." (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.) The Oxygen Sensor (02S) varies the voltage within a range of about 1 volt if the exhaust is rich, down through about .10 volt if exhaust is lean.

The sensor is like an open circuit and produces no voltage when it is below 316°C (600°F). An open sensor circuit or cold sensor causes "OPEN LOOP" operation.

TEST DESCRIPTION: Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 13 will set:

^ Engine at normal operating temperature.
^ At least 2 minutes engine time after start.
^ 02S signal voltage steady between .35 and .55 volt.
^ Throttle position sensor signal above 4%.
^ All conditions must be met for about 60 seconds.

If the conditions for a DTC 13 exist, the system will not go "CLOSED LOOP."

2. This will determine if the sensor is at fault or the wiring or ECM is the cause of the DTC 13.

3. In doing this test use only a high impedance digital volt ohm meter. This test checks the continuity of CKTs 412 and 413 because if CKT 413 is open the ECM voltage on CKT 412 will be over .6 volt (600 mV).

DIAGNOSTIC AIDS:
Normal Tech 1 scan tool voltage varies between 100 mV to 999 mV (.1 and 1.0 volt) while in "CLOSED LOOP." DTC 13 sets in one minute if voltage remains between .35 and .55 volt, but the system will go "OPEN LOOP" in about 15 seconds. - Intermittent Malfunctions