Powertrain Controls - ECM/PCM

*** UPDATED BY TSB 416511, DATED MAY, 1994

DTC 63.:

Right Heated 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 oxygen sensor 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 541. 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.

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

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

1. This test checks the oxygen sensor 5 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 (J 39200). This test checks the continuity of CKT 1666.

DIAGNOSTIC AIDS
Normal Tech 1 (or equivalent) Scanner voltage readings vary between 10 mV to 1000 mV (0.01 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. Testing and Inspection

An oxygen supply inside the H02S is necessary for proper H02S operation. This supply of oxygen is supplied through the HO2S wires. All H02S wires and connections should be inspected for breaks or contamination that could prevent reference oxygen from reaching the HO2S.