Powertrain Controls - ECM/PCM

Diagnostic Trouble Code 63:

Oxygen Sensor Circuit:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) supplies a voltage of about 450 mV between terminals "C8" and "C7" (If measured with a 10 megohm digital voltmeter, this may read as low as 320 mV.). The Heated Oxygen Sensor (HO2S) varies the voltage within a range of about 1000 mV if the exhaust is rich, down through about 10 mV if exhaust is lean.

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. Whenever the ignition is "ON" voltage is supplied to the HO2S heaters on CKT 439. Even with the engine not running, the HO2S will reach operating temperature and indicate the oxygen content of the exhaust gas at the sensor. Typically the signal voltage will be near 450 mV at key-up. The signal voltage will then rise or drop as the sensor becomes active, depending on the oxygen content of the air near the sensor.

DIAGNOSTIC TROUBLE CODE (DTC) 63 WILL SET WHEN
Engine is at normal operating temperature above 70°C (158°F), engine operating more than 2 minutes, oxygen signal voltage steady between 350 mV to 550 mV, throttle position angle above 5% and DTCs 21 and 22 not set. All conditions met for about 60 seconds.

ACTION TAKEN (PCM DEFAULT)
The Malfunction Indicator Lamp (MIL) will illuminate and the fuel control system will go into "Open Loop."

DIAGNOSTIC AIDS
DTC Chart Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. 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 (622°F). An inoperative HO2S heater could cause a DTC 13 to set.

2. This will determine if the oxygen sensor is at fault, or if the cause of the DTC 63 is elsewhere in the circuit.

3. For this test use only a high impedance digital volt ohmmeter (JD 39200). This test checks the continuity of CKT 1666.

DIAGNOSTIC AIDS
Normal Tech 1 scan tool voltage readings vary between 10 mV to 1000 mV (0.010 and 1.0 volt), while in "Closed Loop." The system will go into "Open Loop" operation when DTC 63 sets.

Refer to Diagnosis by Symptom/Intermittents. - Intermittent Malfunctions

An oxygen supply inside the HO2S is necessary for proper operation. This supply of oxygen is supplied through a hole in the HO2S wiring loom grommet. All HO2S connectors should be inspected for contamination that could prevent oxygen from reaching the HO2S.