Diagnostic Procedure

DIAGNOSTIC PROCEDURE FOR DTC 21

1. CHECK VOLTAGE OF TERMINALS HT1, HT2.
- If OK proceed to step 3.
- If not OK proceed to step 2.
2. CHECK RESISTANCE OF MAIN OXYGEN SENSOR.
- If OK check and repair main oxygen sensor heater circuit.
- If not OK replace main heated oxygen sensor.
3. CHECK OPERATION OF MAIN HEATED OXYGEN SENSOR HEATER.
- If OK replace main heated oxygen sensor.
- If not OK check and replace ECM [1].

[1] It is probable the oxygen sensor has deteriorated.