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Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
  1. If QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed and Continuous Memory DTCs P0350-P0354 or DTCs P0300-P0306 are present, repair them first. For other DTCs, go to next step.
  2. Check For HO2S KOER -  If DTCs P1137 or P1138 are present during QUICK TEST, go to next step. If DTCs P1137 or P1138 are not present during QUICK TEST, fault that produced DTC P0136 is intermittent. See INTERMITTENT  testing under SYSTEM TESTS.
  3. Visual Inspection -  Inspect wiring harness for stretched, pinched or corroded wires. DTCs P0136 or P0156 with P1137 and/or P1138 may be caused by exhaust leaks between engine and end of catalyst. Inspect exhaust for holes and cracks. Check exhaust flanges for leaks. Check HO2S torque. If none of these conditions are present, go to next step. If any of these conditions are present, repair as necessary. After repair, go to step  10 .
  4. Check HO2S Harness For Short To VPWR & Ground -  Disconnect scan tool from DLC. Disconnect PCM 104-pin harness connector. Connect breakout box to PCM harness connector only. See Figure . Disconnect rear HO2S connector. Measure resistance between breakout box terminal No. 35 and terminals No. 71 or 97 (short to VPWR). Record reading. Measure resistance between breakout box terminal No. 35 and terminal No. 91 (short to SIG RTN circuit). Record reading. Measure resistance between breakout box terminal No. 35 and terminal No. 90 (short to VREF circuit). Record reading. Measure resistance between breakout box terminal No. 35 and terminal No. 103 (short to PWR GND circuit). Record reading. If each resistance reading is more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, repair short in appropriate wiring harness. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  10 .
  5. Check Resistance Of HO2S SIG & Ground Circuits For Open In Harness -  Measure resistance of HO2S SIG circuit between breakout box terminal No. 35 and HO2S harness connector (White/Black wire). See Fig 1 . Record reading. Measure resistance of HO2S SIG RTN circuit between breakout box terminal No. 91 and HO2S harness connector (Orange wire). Record reading. Measure resistance of HO2S VPWR circuit between breakout box terminal No. 71 or 97 and HO2S 4-pin harness connector (Light Blue/Orange wire). Record reading. If each resistance reading is less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open in appropriate circuit. After repair, go to step  10 .
    Fig 1: HO2S Harness Connector Circuit Identification
    G95E35968Courtesy of MAZDA MOTORS CORP.
  6. Check HO2S Circuit Voltage -  Remove breakout box. Reconnect PCM 104-pin harness connector and rear HO2S 4-pin harness connector. Connect scan tool to DLC. With KOEO, access O2S12 PID. Observe voltage. If voltage reading is more than 1.5 volts, go to step  9 . If voltage reading is 1.5 volts or less, go to next step.
  7. Check Resistance Of HO2S Ground Circuit In PCM -  Turn ignition off. Disconnect PCM 104-pin harness connector. Connect breakout box to PCM. See Figure . Leave vehicle harness disconnected from breakout box. Measure resistance between breakout box terminals No. 91 (SIG RTN circuit) and No. 103 (PWR GND circuit). If resistance reading is less than 5 ohms, go to next step. If resistance reading is 5 ohms or more, replace faulty PCM. After repair, go to step  10 .
  8. Apply 12 Volts To Suspect HO2S Circuit -  Remove breakout box. Connect PCM 104-pin harness connector. Disconnect rear HO2S 4-pin harness connector. Install fused jumper wire between VPWR circuit (Light Blue/Orange wire) and HO2S SIG circuit (White/Black wire) at HO2S 4-pin harness connector. See Fig 1 . With KOEO, access O2S12 PID. Observe voltage reading. If voltage reading is more than 1.5 volts, replace faulty rear HO2S. After repair, go to step  10 . If voltage reading is 1.5 volts or less, replace faulty PCM. After repair, go to step  10 .
  9. Check For Over Voltage On HO2S Circuit In PCM -  Disconnect rear HO2S 4-pin harness connector. With KOEO, measure voltage between SIG RTN circuit (Orange wire) at HO2S 4-pin harness connector and negative battery terminal. See Fig 1 . Record reading. With KOEO, measure voltage between SIG circuit (Orange wire) at HO2S 4-pin harness connector and negative battery terminal. Record reading. If either voltage reading is more than 1.5 volts, replace faulty PCM. After repair, go to next step. If either voltage reading is 1.5 volts or less, replace faulty rear HO2S. After repair, go to next step.
  10. Verify Trouble Shooting Of DTCs Completed -  Make sure all electrical connectors are reconnected. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If the same DTC is present, replace faulty PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTCs are present, test is complete.
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