LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Toyota >> 2003 >> Matrix Base, FWD, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 110 (Engine Control System Self Diagnostics (2UZ-FE)) >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1) & DTC P0430: Catalyst System Efficiency Below Threshold (Bank 2) >> Diagnosis & Repair
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Toyota 4Runner. However, it is still accessible from the selected car via links, so may be relevant.
  1. Using Toyota hand-held tester or scan tool, check for any other DTCs. If only DTCs P0420 and/or P0430 exists, go to next step. If other DTCs exist, diagnose and repair those DTCs first and then retest.
  2. Check exhaust system for leaks. If no exhaust leak exists, go to next step. If exhaust leak exists, repair exhaust system as necessary.
  3. Turn ignition off. Disconnect HO2S 4-pin connector. See Figure. Measure resistance between HO2S 4-pin connector terminals No. 2 (+B) and No. 1 (HT). Make note of measurement. Then, measure resistance between HO2S 4-pin connector terminals No. 1 (HT) No. 4 (E1). See HO2S HEATER RESISTANCE SPECIFICATIONS . If resistance is within specification, replace TWC (in exhaust manifold LH or RH). If resistance is not within specification, replace HO2S. See HEATED OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - V6 & V8 article.
    HO2S HEATER RESISTANCE SPECIFICATIONS

    Terminals No. Resistance in Ohms @ 68F (20C)
    1 (HT) & 2 (B+) 11-16
    1 (HT) & 4 (E1) No Continuity
scientia non olet · About LEMON Manuals