Powertrain Controls - ECM/PCM

CIRCUIT DESCRIPTION
The ECM applies a bias voltage of approximately 450 millivolts (350-550 mV is normal bias voltage) between terminals "GE14" and "GE15." The oxygen (O2) 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. 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 36°C (68°F). An open sensor circuit causes "Open Loop" operation.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Code 13 will set:
^ Engine coolant temperature greater than 70°C (168°F).
^ At least 2 minutes engine run time after start.
^ O2 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.
If the condition for a Code 13 exist, the system will not go "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 (562°F).
3. This will determine if the sensor is at fault or the wiring or ECM is the cause of the Code 13.
4. For this test use only a high impedance digital volt ohmmeter (DVM). 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 0.6 volt (600 mV).
5. If the A/C fuse was blown check the A/C control circuit or generator for short circuits.

DIAGNOSTIC AIDS
Both oxygen sensors and heaters must be working properly to enable "Closed Loop" operation.

Normal "Scan" voltage varies between 100 mV to 999 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, but the system will go "Open Loop" in about 15 seconds.

Refer to "Intermittents" in Symptoms. - Intermittent Malfunctions