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Home >> Mazda >> 2000 >> Protege ES, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 1.8L >> Diagnostic Trouble Code Tests >> DTC P0138: Rear Heated Oxygen Sensor Circuit High Input >> Diagnosis & Repair Procedure

Diagnosis & Repair Procedure

  1. Ensure FREEZE FRAME PID data has been recorded. Check service bulletins. Go to next step.
  2. Turn ignition on. Using scan tool, verify stored DTCs. If any other DTC is present, repair other DTC first. If no other DTCs are present, go to next step.
  3. Verify if DTC P0138 is present in FREEZE FRAME PID data. If DTC is present, go to next step. If DTC is not present, see TROUBLE SHOOTING in BASIC DIAGNOSTIC PROCEDURES article.
  4. Turn ignition off. Disconnect RHO2S connector. Turn ignition on. Check voltage between 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. After repair, go to step  6 .
  5. Reconnect all connectors. Start engine. Using scan tool, monitor RHO2S PID. Accelerate engine at least 10 times. If PID is always more than .45 volts, replace rear heated O2 sensor. If PID is more and less than .45 volts when revving engine, go to next step.
  6. Turn ignition on. Clear DTC from memory. Perform drive modes 1 and 3. See SELF-DIAGNOSTICS - INTRODUCTION - MIATA, MILLENIA, MPV & PROTEGE article. Recheck for DTCs. If same DTC is not pending, go to next step. If same DTC is pending, replace PCM. Go to next step.
  7. Clear DTC from memory. Recheck for DTCs. If any DTC is present, diagnose and repair DTC. If no DTCs are present, test is complete.
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