DTC 13

Code Chart 13:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION:
The Engine Control Module (ECM) supplies a voltage of about .45 volt between terminals "D10" and "D11" (If measured with a 10 megohm digital voltmeter, this may read as low as .32 volt.)

When the Oxygen Sensor (O2S) reaches operating temperature, it varies this voltage from about .1 volt (exhaust is lean) to about .9 volt (exhaust is rich).

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 under the following conditions:

^ Engine at normal operating temperature.
^ At least 40 seconds has elapsed since engine start-up.
^ O2S signal voltage is steady between .35 and .55 volt.
^ Throttle angle is above 5%.
^ All above conditions are met for about 40.3 seconds or more.

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

2. This test determines if the O2S is the problem or if the ECM and wiring are at fault.

3. In doing this test, use only a 10 megohm digital voltmeter. This test checks the continuity of CKT 412 and CKT 413. If CKT 413 is open, the ECM voltage on CKT 412 will be over .6 volt (600 mV).

DIAGNOSTIC AIDS:
Normal Oxygen Sensor (O2S) voltage varies between 100 mV to 999 mV (.1 and 1.0 volt) while in "CLOSED LOOP." DTC 13 sets in one minute if sensor signal voltage remains between .35 and .55 volt, but the system will go to "OPEN LOOP" in about 15 seconds.

Verify a clean, tight ground connection for CKT 413. Open CKT 412 or CKT 413 will result in a DTC 13. If DTC 13 is intermittent, Testing and Inspection