Diagnosis & Repair
- Using Toyota hand-held tester or scan tool, check for any other DTCs. If only DTC P0420 exists, go to next step. If other DTCs exist, diagnose and repair those DTCs first and then retest.
- Check exhaust system for leaks. If no exhaust leak exists, go to next step. If exhaust leak exists, repair exhaust system as necessary.
- Disconnect electrical connector for A/F sensor (bank No. 1, sensor No. 1) located on exhaust manifold above catalytic converter. See Figure. Using ohmmeter, check resistance for heater on A/F sensor between +B and HT terminals on electrical connector for A/F sensor. See Figure. Resistance should be .8-1.4 ohms at 68°F (20°C) and 1.8-3.2 ohms at 1472°F (800°C). If resistance is within specification, go to next step. If resistance is not within specification, replace A/F sensor (bank No. 1, sensor No. 1).
- Disconnect electrical connector for heated oxygen sensor (bank No. 1, sensor No. 2) located on exhaust manifold below catalytic converter. See Figure. Using ohmmeter, check resistance between +B and HT terminals on electrical connector for heater on heated oxygen sensor (bank No. 1, sensor No. 2). See Figure. Resistance should be 11-16 ohms at 68°F (20°C) and 23-32 ohms at 1472°F (800°C). If resistance is within specification, replace catalytic converters along with exhaust manifold. If resistance is not within specification, replace heated oxygen sensor (bank No. 1, sensor No. 2).
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