Powertrain Controls - ECM/PCM

Trouble Code 13 Chart:

Heated Oxygen Sensor Schematic:

CIRCUIT DESCRIPTION
The heated oxygen sensor has 450 millivolts applied to it by the PCM on CKT 412. This voltage may vary slightly when measured with a 10 megohm (minimum) impedance DVM. As the HO2S warms and becomes active, it also produces a voltage which will vary from 100 to 1000 millivolts. The PCM then detects whichever voltage is greater at the HO2S signal input. If the HO2S voltage is less than the 450 millivolts reference, the sensor acts as a ground and functionally reduces the voltage level at the input. This effect causes the Tech 1 scan tool to display a 100 to 1000 millivolt operating range.

The heater in the HO2S allows for faster sensor warm-up and better temperature stabilization during engine operation.

DTC 13 Will Set When: The engine is in "Closed Loop," ECT is greater than 65°C (149°F), no current DTC 21 or 22, HO2S voltage is between 350 and 550 millivolts, throttle angle is greater than 3% with all conditions met for 30 seconds.

Action Taken (PCM will default to): The PCM will default to "Open Loop" operation and the MIL will become illuminated.

DTC 13 Will Clear When: A current DTC 13 will clear when the HO2S voltage begins to vary outside of the 350 to 550 millivolt window. A History DTC 13 will clear after 50 ignition key cycles without a current DTC 13 being stored.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. If the conditions for a DTC 13 exist, the system will not go "Closed Loop."
2. This will determine if the sensor is at fault, or the wiring or PCM is the cause of the DTC 13.
3. In doing this test use only a high impedance digital volt ohmmeter. This test checks the continuity of CKT 412 and CKT 413 because if CKT 413 is open, the PCM voltage on CKT 412 will be over .6 volt (600 mV).

DIAGNOSTIC AIDS:
Normal Tech 1 scan voltage varies between 100 mV to 999 mV (.1 and 1.0 volt) while in "Closed Loop." DTC 13 sets if voltage remains between .35 and .55 volt, but the system will go "Open Loop" in about 15 seconds. Refer to "Diagnosis by Symptoms". Testing and Inspection