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Test TC-112A - Catalyst 1/1 Efficiency Failure

NOTE: For connector terminal ID, see CONNECTOR IDENTIFICATION DIRECTORY. For component location see wiring diagram in the WIRING DIAGRAMS article.
NOTE: 1/1 Heated Oxygen Sensor (HO2S) is located in upstream position. On models equipped with 2 upstream HO2S, 1/1 HO2S is located in left upstream position. 1/2 HO2S is located in downstream position. On models equipped with 4 HO2S, 1/2 HO2S is located in left downstream position.
  1. Using scan tool, read DTCs. If scan tool displays any HO2S related DTCs, see DTC MESSAGES & CODES table in DTC TEST and perform appropriate test(s). If no HO2S related DTCs are displayed, go to next step.
  2. Check if any Technical Service Bulletins (TSBs) apply to vehicle. If a TSB exists, perform corrective action and perform TEST VER-5A. If no TSBs exist, go to next step.
  3. CATALYTIC CONVERTER EFFICIENCY FAILURE DTC sets in Powertrain Control Module (PCM) as catalytic converter loses ability to store oxygen and concentration of oxygen becomes the same downstream (after catalytic converter) as upstream (before catalytic converter). Output voltage of downstream O2S becomes the same as upstream O2S with a time lag seen by PCM between switching of O2S. Go to next step.
  4. Malfunction Indicator Light (MIL) on instrument panel will illuminate after 2 trips and remain on, but goes off if conditions required to set DTC are not found on subsequent trips. Possible causes are: defective catalytic converter, exhaust leaks before catalytic converter, contaminated fuel or engine mechanical problem. Go to next step.
  5. Start engine. Check for exhaust leaks between engine and 1/2 HO2S. Repair exhaust leaks as necessary and perform TEST VER-5A. If no exhaust leaks exist, go to next step.
  6. Check for excessive smoke caused by high oil or coolant consumption. Repair engine mechanical condition as necessary, replace catalytic converter and HO2Ss, and perform TEST VER-5A. If engine is okay, go to next step.
    NOTE: A newly installed 1/2 HO2S with an existing, aging 1/1 HO2S may cause this DTC to be set.
  7. If 1/2 HO2S has been not been replaced within last 5000 miles, replace catalytic converter and perform TEST VER-5A. If 1/2 HO2S has been replaced within last 5000 miles, go to next step.
  8. If 1/1 HO2S has been replaced within last 5000 miles, replace catalytic converter and perform TEST VER-5A. If 1/1 HO2S has not been replaced within last 5000 miles, replace 1/1 HO2S and perform TEST VER-5A.
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