Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 13:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The Engine Control Module (ECM) supplies a voltage of about 0.45 volt between terminals "C13" and "C14." (If measured with a 10 megohm digital voltmeter, this may indicate as low as 0.32 volt). The Oxygen Sensor (O2S) outputs about 1 volt if a rich O2S signal is indicated, down through about 0.10 volt if a lean O2S signal is indicated.

The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit or cold sensor causes "Open Loop" operation.

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

1. Diagnostic Test Code (DTC) 13 will set:

^ Coolant temperature above 70°C (158°F)
^ At least 2 minutes engine run time after start
^ O2S signal voltage steady between 0.35 and 0.55 volt
^ Throttle position sensor signal above 5% (about 0.3 volt above closed throttle voltage)
^ All conditions must be met for about 60 seconds

NOTE: If the conditions for a DTC 13 exist, the system will not go into "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. To perform this test, use only a high impedance digital volt ohmmeter. 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 0.60 volt (600 mV).

DIAGNOSTIC AIDS
Normal scan tool voltage readings vary between 100 mV to 1000 mV (0.1 to 1.0 volt), while in "Closed Loop." DTC 13 sets in one minute if voltage remains between 0.35 and 0.55 volt, the system will go "Open Loop" in about 15 seconds.

Refer to Intermittents in Diagnosis by Symptom. Testing and Inspection