Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Toyota Tacoma. However, it is still accessible from the selected car via links, so may be relevant.

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

For preliminary inspection with Toyota Hand-held tester or Enhanced OBD II scan tool, see Fig 2. The preliminary inspection procedure of A/F CONTROL enables an output voltage check of A/F sensor and heated oxygen sensor. Use these HINTS during preliminary inspection:

A low A/F sensor voltage could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.
A high A/F sensor voltage could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.

For diagnosis and repair procedure, see Fig 3-Fig 8 . When instructed to "Perform Confirmation Driving Pattern", go to TEST DRIVE CONFIRMATION .

For A/F sensor circuit wiring diagram, see Fig 1. When access to, or replacement of ECM is necessary, Engine Control Module (ECM) is located behind glove box. See Figure. For ECM connector terminal view, see Figure. For testing of systems or components, see SYSTEM & COMPONENT TESTING - 4-CYLINDER article. For removal and installation of components, see REMOVAL, OVERHAUL & INSTALLATION - 4-CYLINDER article.

Fig 1: Oxygen Sensor & A/F Sensor Circuit Wiring Diagram