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Home >> Mazda >> 2003 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 26 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0138: Ho2S (Rear) Circuit, High Input >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

WARNING: This page is about a different car, the 2002 Mazda Protege5 and 2002 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
  1. Turn ignition off. Connect scan tool to DLC-2. Turn ignition on, engine off. Monitor for FREEZE FRAME DATA and ensure data has been recorded. Check service bulletins for repair information related to this DTC. If repair information is not available, go to next step. If repair information is available, perform diagnosis and repair as necessary. After repair, go to step  6.
  2. Turn ignition switch off and then start engine. Using scan tool, check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If any other DTCs are present, go to appropriate test. If no other DTCs are present, go to next step.
  3. Check if DTC P0138 is present in FREEZE FRAME DATA. If DTC is present, go to next step. If DTC is not present, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - NO CODES article.
  4. Turn ignition switch off. Disconnect rear HO2S connector. Turn ignition switch on. Measure voltage between HO2S harness connector terminal "A" (Yellow/Blue wire) and ground. If voltage is not present, go to next step. If voltage is present, repair short to power on Yellow/Blue wire between rear HO2S harness connector terminal "A" and PCM 104-pin harness connector terminal No. 35. See Figure and Fig 1 . See WIRING DIAGRAMS article. Go to step  6.
    Fig 1: Identifying Rear HO2S Harness Connector Heater Terminals
    G00143768Courtesy of MAZDA MOTORS CORP.
  5. Start engine. Using scan tool, access O2S12 PID data. Race engine at least 10 times in neutral. If O2S12 PID stays at more than .45 volt, replace rear HO2S. If O2S12 PID does not stay at .45 volt, go to next step.
  6. Reconnect all connectors. Turn ignition switch on. Clear DTCs. See CLEARING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. Perform DRIVE MODE 1 - PCM ADAPTIVE MEMORY  and DRIVE MODE 3 - HO2S, HO2S HEATER & TWC REPAIR VERIFICATION  . Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If DTC P0138 is present, replace PCM and go to next step. If DTC P0138 is not present, go to next step.
  7. Cycle ignition switch from off to on. Check for DTCs. See RETRIEVING DIAGNOSTIC TROUBLE CODES  under SELF-DIAGNOSTIC SYSTEM. If no other DTCs are present, testing is complete. If any other DTC is present, go to applicable test and repair.
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