Diagnosis & Repair

NOTE: Using Toyota hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.

To aid in diagnosis of deteriorated catalyst, it is recommended to perform Confirmation Engine Racing Pattern while observing HO2S waveform pattern. See CONFIRMATION ENGINE RACING PATTERN .

For diagnosis and repair procedure, see Fig 1. For A/F sensor heater test, see Fig 2. For HO2S heater test, see Fig 3.

For access to, or replacement of ECM, Engine Control Module (ECM) is located behind glove box. See Figure. For ECM connector view, see Figure. For testing of systems or components, see SYSTEM & COMPONENT TESTING - V6 & V8 article. For removal and installation of components, see REMOVAL & INSTALLATION - V6 & V8 article.

Fig 1: DTC P0420 Diagnostic Procedure

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Fig 2: Testing A/F Sensor & Heated Oxygen Sensor (Banks 1 & 2 Sensor 1)

Fig 3: Testing Heated Oxygen Sensor (Bank 1 Sensor 2) Heater