Powertrain Controls - ECM/PCM

DTC 13 Chart (PCM):

HO2S Circuit (PCM):

Circuit Description:
The control module applies a bias voltage of approximately 450 millivolts (350-550 mV is normal bias voltage) between terminals "A10" and "A12". The Oxygen (02) sensor varies the voltage within a range of about 1 volt if the exhaust is rich, and down through about 0.010 volt if exhaust is lean. Code 13 is set when the voltage does not vary on CKT 412 within a predetermined amount of time. The sensor is like an open circuit and produces no voltage when it is below 315°C (600°F). An open sensor circuit, or a cold sensor causes "Open Loop" operation.

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.

1. Code 13 will set:

^ Engine has been running longer than 2 minutes.

^ Engine coolant temperature greater than 70°C (158°F).

^ Throttle position sensor signal has been above 5% for 60 seconds or longer.

^ O2 signal voltage steady between 0.35 and 0.55 volt. If the conditions for a Code 13 or Code 63 exist, the system will not go into "Closed Loop."

2. This test checks the oxygen sensor's heating element. The heating element resistance should be 3.5 ohms at 20°C (68°F) or 14 ohms at 350°C (662°F).

3. This will determine if the sensor is at fault.

4. For this test use only a high impedance Digital Volt Ohmmeter (DVM). This test cheeks the continuity of CKT 412 and CKT 413. If CKT 413 is open, the control module voltage on CKT 412 will be over 0.6 volt (600 mV).

5. If the fuse was open, cheek the control module wiring diagram for complete wiring circuit.


Diagnostic Aids:
If the oxygen sensor heaters are not operating properly, system may go into "Open Loop" after extended idle.

Normal Tech 1 "Scan" tool voltage varies between 100 mV to 1000 mV (0.1 and 1.0 volt), while in "Closed Loop." Code 13 sets in one minute if voltage remains between 0.35 and 0.55 volt, however the system will go "Open Loop" in about 15 seconds.- Intermittent Malfunctions


An oxygen supply inside the 02 sensor is necessary for proper 02 sensor operation. This supply of oxygen is supplied through the 02 sensor wires. All 02 sensor wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the 02 sensor.