Diagnosis & Repair

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

NOTE: After confirming DTC P0125, use Toyota hand-held tester or scan tool to access CURRENT DATA to read heated oxygen sensor (B1 S1) output voltage. If output voltage is always less than 0.1 volt, heated oxygen sensor (B1 S1) circuit may be open or shorted. Using hand-held tester or scan tool, read FREEZE FRAME data. Freeze frame data records engine conditions when malfunction is detected.

For diagnosis and repair procedure, see Fig 2-Fig 4 . For confirmation driving pattern, see TEST DRIVE CONFIRMATION .

For HO2S circuit wiring diagram, see Fig 1. For ECM location, see Figure. For ECM connector terminal view, see Figure.

To identify circuits referenced in testing, see ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. For vacuum or EVAP hose routing, see VACUUM DIAGRAMS article. For testing of systems or components, see BASIC DIAGNOSTIC PROCEDURES - 4-CYLINDER article or SYSTEM & COMPONENT TESTING - 4-CYLINDER article. For removal and installation of components, see REMOVAL & INSTALLATION - 4-CYLINDER article.

Fig 1: HO2S Circuit Wiring Diagram

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Fig 2: DTC P0125 Diagnostic Procedure (Steps 1-3)

Fig 3: DTC P0125 Diagnostic Procedure (Steps 4-8)

Fig 4: DTC P0125 Diagnostic Procedure (Steps 9-12)