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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, go to next step.
  2. DTCs P1131 & P1151: Upstream HO2S(s) Not Switching -  Check air intake system for leaks and damage. Verify integrity of PCV system. Refer to POSITIVE CRANKCASE VENTILATION under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - B2300, B3000, B4000 & TRIBUTE article. Check for vacuum leaks. If any problems are found, repair as necessary. After repair, go to step  21 . If no problems are found, go to next step.
  3. Perform KOER Self-Test -  Disconnect fuel vapor hose from intake manifold. Plug fitting at intake manifold. Start engine and run at 2000 RPM for 5 minutes, then return to idle. Perform KOER Self-Test. If DTC P1131 and/or P1151 are set, go to next step. If DTC P1131 and/or P1151 are not set, perform EVAP Leak Test to locate EVAP system leak. See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM & COMPONENT TESTING - B2300, B3000, B4000 & TRIBUTE article.
    CAUTION: During next test step, when connecting a jumper wire, if a spark occurs (indicating a short circuit), remove fused jumper wire. Check for a short to ground. Also check heater fuse.
  4. HO2S Circuit Test (With Lean DTCs) -  Turn ignition off. Disconnect suspect HO2S 4-pin harness connector related to DTC:
    • P1131, HO2S11 (Front Right)
    • P1151, HO2S21 (Front Left)
    With KOEO, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access and observe O2S11 (Front Right) or O2S21 (Front Left) PID. Connect fused jumper wire between appropriate HO2S SIG circuit and HO2S VPWR circuit at HO2S 4-pin harness connector. If voltage reading is 1.3 volts or more, go to next step. If voltage reading is less than 1.3 volts, an open or short circuit to ground is present in vehicle wiring harness or PCM. Go to step  7 .
  5. Check Signal Return Circuit For Shorts & Opens -  Turn ignition off. Measure resistance of HO2S SIG RTN circuit between HO2S 4-pin harness connector and negative battery terminal. See Fig 1 . If resistance reading is less than 5 ohms, reconnect all components. Go to step  10 . If resistance reading is 5 ohms or more, check wiring for an open or short circuit to ground. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to next step.
    Fig 1: HO2S Harness Connector Circuit Identification
    G95E35968Courtesy of MAZDA MOTORS CORP.
  6. Check HO2S Signal Return Circuit In Vehicle Harness -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance of HO2S SIG RTN circuit between breakout box terminal No. 91 and HO2S 4-pin harness connector. If resistance reading is less than 5 ohms, replace faulty PCM. After repair, go to step  21 . If resistance reading is 5 ohms or more, repair open circuit. After repair, go to step  21 .
  7. Check Resistance Of HO2S Ground Circuits -  Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Measure resistance of appropriate HO2S SIG circuit between breakout box terminal No. 60 (HO2S11 circuit) or No. 87 (HO2S21 circuit) and HO2S 4-pin harness connector. See Fig 1 . If resistance reading is less than 5 ohms, go to next step. If resistance reading is 5 ohms or more, repair open circuit. After repair, go to step  21 .
  8. Check HO2S Circuit Wiring Harness For Short To Ground -  Measure resistance of appropriate HO2S SIG circuit between breakout box terminal No. 60 (HO2S11 circuit) or No. 87 (HO2S21 circuit) and breakout box terminal No. 103 (PWR GND circuit). Record reading. Measure resistance of appropriate HO2S SIG circuit between breakout box terminal No. 60 (HO2S11 circuit) or No. 87 (HO2S21 circuit) and breakout box terminal No. 91 (SIG RTN circuit). Record reading. If each resistance reading is more than 10,000 ohms, go to next step. If each resistance reading is 10,000 ohms or less, repair short circuit. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  21 .
  9. Check HO2S For Short To Ground -  Reconnect HO2S 4-pin harness connector. Measure resistance of HO2S SIG circuit between appropriate breakout box terminal No. 60 (HO2S11 circuit) or No. 87 (HO2S21 circuit) and breakout box terminal No. 103 (PWR GND circuit). Record reading. Measure resistance of appropriate HO2S SIG circuit between breakout box terminal No. 60 (HO2S11 circuit) or No. 87 (HO2S21 circuit) and breakout box terminal No. 91 (SIG RTN circuit). Record reading. If each resistance reading is more than 10,000 ohms, replace faulty PCM. After repair, go to step  21 . If either resistance reading is 10,000 ohms or less, replace faulty HO2S. After repair, go to step  21 .
  10. Check HO2S Ability To Generate A Voltage Of More Than 0.5 Volt -  Inspect HO2S harness for chafing, burned wiring or other damage. Repair as necessary. Disconnect suspect HO2S 4-pin harness connector. Connect a DVOM between HO2S 4-pin connector (component side) SIG circuit and SIG RTN circuit or GND circuit. See Fig 1 . Run engine at 2000 RPM for 3 minutes. Run KOER Self-Test and monitor HO2S voltage. Turn ignition off. If voltage reading is more than 0.5 volt during test or at end of self-test, go to next step. If voltage reading is 0.5 volt or less during test or at end of self-test, replace faulty HO2S. After repair, go to step  21 .
  11. Monitor HO2S (PID) For Proper Switching -  Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access O2S11 (Front Right) or O2S21 (Front Left) PID while wiggling, bending and shaking small sections of engine wiring harness from HO2S to PCM. Turn ignition off. If HO2S voltage reading stays high (more than 0.45 volt) or stays low (less then 0.45 volt), isolate cause of HO2S not switching. Repair as necessary. After repair, go to step  21 . If HO2S voltage reading does not stay high (more than 0.45 volt) or stay low (less then 0.45 volt), go to next step.
    WARNING: Fuel system retains fuel pressure with engine not running. Use caution when working on fuel system.
  12. Check Fuel Pressure -  Install fuel pressure gauge. With KOEO, using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select ACTIVE COMMAND MODES. Access OUTPUT TEST MODE and run fuel pump to obtain maximum fuel pressure. Fuel pump will run for approximately 8 seconds when OUTPUT TEST MODE is activated. See FUEL PRESSURE SPECIFICATIONS  table. If fuel pressure is within specification, fuel system is okay. Go to next step. If fuel pressure is not within specification, see FUEL DELIVERY SYSTEM  testing under SYSTEM TESTS.
    FUEL PRESSURE SPECIFICATIONS

    Engine psi (kPa)
    2.3L 35-55 (240-380)
    3.0L & 4.0L 30-65 (207-448)
  13. Check Injector Fault PIDs -  Using scan tool, access INJ1F-INJ6F PIDs. If an injector fault is present, go to next step. If an injector fault is not present, go to step  17 .
    14. NOTE: Next test step erases Continuous Memory DTCs.
    Fig 2: Fuel Injector Harness Connector Circuit Identification
    G00155536Courtesy of MAZDA MOTORS CORP.
  14. Check Fuel Injector(s) & Harness Resistance -  Turn ignition off. Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure . Use injector fault PID to determine which fuel injector(s) to test. Measure resistance of suspect fuel injector between INJ circuit and breakout box terminal No. 71 (VPWR circuit). See Fig 2 . See FUEL INJECTOR RESISTANCE SPECIFICATIONS  table. If resistance reading is within specification, replace faulty PCM. After repair, go to step  21 . If resistance reading is not within specification, go to next step.
    FUEL INJECTOR RESISTANCE SPECIFICATIONS

    Engine Ohms
    2.3L 11-13
    3.0L 8.5-15.5
    4.0L 11-18
  15. Check Fuel Injector Harness Resistance -  Disconnect fuel injector 2-pin harness connector at suspect fuel injector. Measure resistance of VPWR circuit between breakout box terminal No. 71 and fuel injector harness connector. See Fig 2 . Record reading. Measure resistance of INJ circuit between appropriate breakout box terminal and fuel injector harness connector. See Fig 2 . Record reading. If each resistance reading is less than 5 ohms, go to next step. If each resistance reading is 5 ohms or more, repair open circuit in suspect wiring harness. See appropriate WIRING DIAGRAM under ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS. After repair, go to step  21 .
  16. Check Fuel Injector Harness Circuit For Short To Power & Ground -  Measure resistance between suspect INJ circuit harness connector and breakout box terminals No. 71 or 97. See Fig 2 . Record reading. Measure resistance between suspect INJ circuit harness connector and breakout box terminals No. 51 or 103. See Fig 2 . Record reading. If each resistance reading is more than 10,000 ohms, go to next step. If either resistance reading is 10,000 ohms or less, repair short circuit. After repair, go to step  21 .
  17. Flow Test Fuel Injector(s) -  Using a fuel injector tester, flow test fuel injectors following equipment manufacturers instructions. See FUEL INJECTOR FLOW RATE SPECIFICATIONS  table. If flow rate values are within specification, go to next step. If flow rate values are not within specification, replace faulty fuel injector(s). After repair, go to step  21 .
    FUEL INJECTOR FLOW RATE SPECIFICATIONS

    Engine Lbs. Hr. (kg/hr)
    2.3L 21 (9.6)
    3.0L 12 (5.5)
    4.0L 19 (8.7)
  18. Inspect Induction System For Air Leaks -  Inspect following areas for signs of air leaks:
    • Inlet tube(s) from air cleaner to throttle body assembly.
    • Gaskets between upper and lower intake manifold assemblies.
    • Vacuum hoses and lines for cracks and proper connections.
    • PCV system integrity.
    If any leak is found, repair as necessary. After repair, go to step  21 . If no leak is found, go to next step.
  19. Check Cylinder Compression -  Check cylinder compression. See MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If cylinder compression is within specification, go to next step. If cylinder compression is not within specification, repair as necessary. After repair, go to step  21 .
    20. NOTE: Next test step requires a helper to monitor PID.
  20. Test Drive While Monitoring HO2S PID For Proper Switching -  Using scan tool, access O2S11 (Front Right) or O2S21 (Front Left) PID. While observer monitors PID, test drive vehicle under different road conditions in an attempt to simulate original fault. If HO2S appears to switch properly, unable to duplicate fault at this time. Go to next step. If HO2S does not appear to switch properly, replace faulty HO2S. After repair, go to next step.
  21. Verify Trouble Shooting Of DTCs Completed -  Reconnect all electrical connectors. Clear DTCs from PCM memory using scan tool. Perform QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If same DTC is present, replace faulty PCM. Repeat QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If any other DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no DTC is present, trouble shooting is complete.
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