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Home >> Toyota >> 2004 >> Matrix Base, FWD, Standard >> Repair and Diagnosis (Single Page) >> External Pages >> Different car >> Section 128 (Engine Control System Self Diagnostics) >> Diagnostic Tests >> DTC P0420: Catalyst System Efficiency Below Threshold (Bank No. 1) >> Diagnosis & Repair
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Diagnosis & Repair

WARNING: This page is about a different car, the 2003 Toyota Matrix and 2003 Toyota Corolla. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: Read freeze frame data using hand-held tester or OBD II scan tool, as freeze frame data records engine conditions when malfunction is detected. When trouble shooting, it is useful for determining whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.
  1. Read DTC output (besides P0420) with hand-held tester or OBD II scan tool. If DTC P0420 is output, go to next step. If DTC P0420 and other codes are output, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Check for an exhaust gas leak. If results are OK, go to next step. If results are not good, repair or replace.
  3. Check oxygen sensor (bank No. 1 sensor No. 1). See SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If results are OK, go to next step. If results are not good, repair or replace oxygen sensor. See REMOVAL & INSTALLATION - 4-CYLINDER article.
  4. Check oxygen sensor (bank No. 1 sensor No. 2). See SYSTEM & COMPONENT TESTING - 4-CYLINDER article. If results are OK, replace front exhaust pipe assembly. If results are not good, repair or replace oxygen sensor. See REMOVAL & INSTALLATION - 4-CYLINDER article.
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