Diagnostic Procedure

DTC 21 Main Heated Oxygen Sensor Circuit

CIRCUIT DIAGRAM





PROCEDURE
1. ARE THERE ANY OTHER CODES (BESIDES DTC 21) BEING OUTPUT?
- If YES go to relevant "Trouble Code Chart".
- If NO replace main oxygen sensor.

INSPECTION USING OSCILLOSCOPE




- With the engine racing (4,000 rpm) measure wave form between terminals OX1 and E1 of Engine Control Module.

- The correct waveform appears as shown in the illustration, oscillating between approximately 0.1 volts and 0.9 volts.

- If the oxygen sensor is deteriorated, the amplitude of the voltage is reduced as shown on the left.