DTC 13

DTC 13 Circuit Diagram:

DTC 13 Diagnostic Chart Open Or Grounded O2 Sensor Circuit:

CIRCUIT DESCRIPTION:

The ECM supplies a voltage of about of 0.45 volt between terminal D7 and D6. (If measured with a 10 megohm digital voltmeter, this may read as low as 0.32 volts). The oxygen sensor varies the voltage within a range of about 1 volt, if the exhaust is rich, down through about 0.10 volt, if exhaust is lean. the O2 sensor has a heater incorporated as part of the sensor. The heater is used to heat the sensor, thus causing the sensor to create voltage sooner so the ECM can monitor the exhaust gasses. This allows the system to go into closed loop sooner. The heater portion of the sensor will not affect code 13. The sensor is like an open circuit and produces no voltage, when it is below 360°C (600°F). An open sensor circuit, or cold sensor, causes "OPEN LOOP" operation.

TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Code 13 will set if:

a. Engine at normal operating temperature above 70°C.
b. At least 120 seconds engine run time after start.
c. Oxygen sensor signal voltage steady between 0.42 and 0.55 volts.
d. Throttle angle above 10%.
f. All conditions must be met for about 4 seconds. If the conditions for a Code 13 exist, the system will not go into "CLOSED LOOP."

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

3. Use only a high impedance (10 megohm) digital volt ohmmeter when performing this test. This test checks the continuity of CKT's D7 and D6. If D6 is open, the ECM voltage on D7 will be over 0.6 volt (600 mV).

DIAGNOSTIC AIDS:

Normal voltage on CKT D7 varies between 100 mV and 999 mV (0.1 and 1.0 volt), while in "CLOSED LOOP." Code 13 sets within one minute, if voltage remains between 0 and 0.347 volt, but the system will go "OPEN LOOP" in about 15 seconds. Verify a clean, tight ground connection for CKT D6. Open CKT(s) D6 or D7 will result in a Code 13. If Code 13 is intermittent,
Intermittant Check Procedure