Inspection Procedure

DTC 21 Main Heated Oxygen Sensor Circuit

INSPECTION PROCEDURE
Are there any other codes (besides DTC 21) being output?
- If YES go to relevant diagnostic trouble code chart.
- If NO Replace main oxygen sensor.

INSPECTION USING OSCILLOSCOPE

A Good Oxygen Sensor Waveform:

- With the engine racing (2,500 rpm) measure waveform between terminals OX1 and E1 of engine control module.
HINT: The correct waveform appears as shown in the illustration , oscillating between approx. 0.1 volt and 0.9 volt.

A Lazy Oxygen Sensor Waveform:

- If the oxygen sensor has deteriorated, the amplitude of the voltage will be reduced as illustrated.

NOTICE: A set driving pattern is necessary for detection this trouble code. Be sure to follow that pattern when performing a test drive to confirm repair. For a description of the prescribed driving pattern, refer to DTC 21: Description.