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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Mazda Tribute. 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. See POSITIVE CRANKCASE VENTILATION SYSTEM  in SYSTEM TESTS . Check for vacuum leaks. If any concerns are present, repair as necessary. After repair, go to step  21. If concerns are not present, go to next step.

  3. Perform KOER Self-Test

    Disconnect fuel vapor hose from intake manifold and plug fitting at intake manifold. Start engine and run at 2000 RPM for 5 minutes and return to idle. Perform KOER self-test. If DTC P1131 and/or P1151 is present, go to next step. If DTC P1131 and/or P1151 are not present, perform EVAP Emissions System Leak Test to locate leak. Refer to EVAPORATIVE EMISSIONS SYSTEM LEAK TEST under SYSTEM TESTS (EVAPORATIVE EMISSION) in SYSTEM & COMPONENT TESTING - B2300, B3000, B4000 & TRIBUTE article.

  4. HO2S Circuit Test (With Lean DTCs)

    Turn ignition off. Disconnect suspect HO2S 4-pin harness connector related to DTC.
    • P1131 = HO2S11 (Front Bank 1)
    • P1151 = HO2S21 (Front Bank 2)

    Turn ignition on, engine off. Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PIN/DATA MONITOR AND RECORD. Access O2S11 (Front Bank 1) or O2S21 (Front Bank 2) PID. Connect fused jumper wire between HO2S SIG and HO2S VPWR at HO2S 4-pin harness connector. If voltage reading is 1.3 volts or more, go to next step. If voltage reading is not as specified, go to step  7.

    NOTE: If a spark occurs, indicating a short, remove fused jumper wire and check for short to ground (check fuse in heater circuit).

  5. Check Signal Return Circuit For Shorts And Opens

    Measure resistance of HO2S SIG RTN circuit (Orange wire) between HO2S 4-pin harness connector and battery ground terminal. If resistance reading is less than 5 ohms, reconnect all connectors and go to step  10. If resistance reading is not as specified, repair Orange wire for open or short to ground between PCM 104-pin harness connector terminal No. 91 and HO2S 4-pin harness connector. After repair, go to next step.

  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 (Orange wire). If resistance reading is less than 5 ohms, replace PCM. After repair, go to step  21. If resistance reading is not as specified, repair open circuit in Orange wire between PCM 104-pin harness connector terminal No. 91 and HO2S 4-pin harness connector. 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 HO2S SIG circuit between breakout box terminal and HO2S 4-pin harness connector (Red/Black wire). Use following terminal assignment and record reading:
    • HO2S-11 SIG = Terminal No. 60
    • HO2S-21 SIG = Terminal No. 87

    If resistance reading is less than 5 ohms, go to next step. If resistance reading is not as specified, repair open circuit. See WIRING DIAGRAMS article. After repair, go to step  21.

  8. Check HO2S Circuit Wiring Harness For Short To Ground

    Measure resistance of HO2S SIG circuit between breakout box terminal No. 60 or 87 and terminal No. 103 (PWR GND). Measure resistance of HO2S SIG circuit between breakout box terminal No. 60 or 87 and terminal No. 91 (SIG RTN). If each resistance reading is more than 10,000 ohms, go to next step. If each resistance reading is not as specified, repair short circuit. 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 breakout box terminal No. 60 or 87 and terminal No. 103 (PWR GND). Measure resistance of HO2S SIG circuit between breakout box terminal No. 60 or 87 and terminal No. 91 (SIG RTN). If resistance reading is more than 10,000 ohms, go to next step. If resistance reading is not as specified, repair short circuit. See WIRING DIAGRAMS article. After repair, go to step  21.

  10. Check HO2S Ability To Generate A Voltage Greater Than 0.5 Volt

    Inspect HO2S harness for chafing, burned wiring or other damage and repair as necessary. Disconnect suspect HO2S from vehicle harness. Connect DVOM to HO2S SIG RTN or HO2S GND at HO2S sensor 4-pin connector. See Figure. Run engine at 2000 RPM for 3 minutes. Run KOER self-test and monitor HO2S voltage. Turn ignition off. If voltage reading was more than 0.5 volt during or at end of Self-Test, go to next step. If voltage reading was not as specified, replace HO2S. After repair, go to step  21.

  11. Monitor HO2S (PID) For Proper Switching

    Start engine. Warm up engine to operating temperature. Using scan, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITOR AND RECORD. Access O2S11 (Front Bank 1) or O2S21 (Front Bank 2) PID and monitor while wiggling, bending and shaking small sections of engine harness from HO2S to PCM. Turn ignition off. If HO2S voltage reading did not stay high (more than 0.45 volt) or low (less than 0.45 volt), go to next step. If HO2S voltage reading stayed high or low, isolate cause for lack of switching and repair as necessary. After repair, go to step  21.
    WARNING: Fuel system is pressurized when engine is not running. To prevent injury or fire, use caution when working on fuel system.
    NOTE: During next step, fuel pump will only operate for approximately 8 seconds when Output Test Mode is selected and activated.

  12. Check Fuel Pressure

    Install fuel pressure gauge. Turn ignition on, engine off. 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. If fuel pressure is 55-70 psi, go to next step. If fuel pressure is not as specified, refer to FUEL DELIVERY SYSTEM  testing under SYSTEM TESTS .

  13. Check Injector Fault PIDs

    Access INJ1F-INJ6F PIDs. If an injector(s) fault is present, go to next step. If an injector fault is not present, go to step  17.
    NOTE: Performing following procedure erases Continuous Memory DTCs.
    NOTE: Use injector fault PID to determine fuel injector circuit(s) requiring testing.

  14. Check Fuel Injector(s) & Harness Resistance

    Disconnect PCM 104-pin harness connector. Connect Breakout Box (49-UN01-130) to PCM harness connector only. See Figure. Measure resistance of suspect fuel injector between suspect INJ circuit breakout box terminal and breakout box terminal No. 71 (VPWR). If resistance reading is 11-18 ohms, replace PCM. After repair, go to step  21. If resistance reading is not within specification, go to next step.

  15. Check Fuel Injector Harness Resistance

    Disconnect fuel injector harness connector at suspect fuel injector. Measure resistance of VPWR circuit (Red wire) between breakout box terminal No. 71 and fuel injector harness connector. Measure resistance of INJ circuit between appropriate breakout box terminal and fuel injector harness connector. See Figure. If each resistance reading is less than 5 ohms, go to next step. If each resistance reading is not as specified, repair open circuit. See WIRING DIAGRAMS article. After repair, go to step  21.

  16. Check Fuel Injector Harness Circuit For Short To Power & Ground

    Measure resistance between suspect INJ circuit breakout box terminal and breakout box terminal No. 71 (VPWR). Measure resistance between suspect INJ circuit breakout box terminal and breakout box terminal No. 103 (PWR GND). If each resistance reading is more than 10,000 ohms, go to next step. If each resistance reading is not as specified, repair short circuit. After repair, go to step  21.

  17. Flow Test Fuel Injector(s)

    Use a fuel injector tester to flow test fuel injectors according to instructions for tester. Flow rate specification is 17 lb/hr (7.8 kg/hr) for 2.0L engines and 22 lb/hr (10.1 kg/hr) for 3.0L engines. If leakage and flow are within specification, go to next step. If leakage and flow are not within specification, replace fuel injector(s). After repair, go to step  21.

  18. Inspect Induction System For Air Leaks

    Inspect following areas for signs of air leaks:
    • Inlet tube(s) from air cleaner to throttle body.
    • Gaskets which seal upper and lower intake manifold.
    • Vacuum hoses and lines for cracks and proper connections.
    • PCV system.

    If there are no signs of leakage or damage, go to next step. If there are any signs of leaks or damage, repair as necessary. After repair, go to step  21.

    NOTE: Use Misfire DTCs (if present) to determine which cylinder's compression to check. Otherwise check all cylinders.

  19. Check Cylinder Compression

    Check cylinder compression. Refer to MECHANICAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS in BASIC DIAGNOSTIC PROCEDURES article. If cylinder compression readings are within specification, go to next step. If cylinder compression readings are not within specification, repair as necessary. After repair, go to step  21.

  20. Test Drive While Monitoring HO2S PID For Proper Switching

    Using scan tool, select DIAGNOSTIC DATA LINK. Select PCM. Select PID/DATA MONITTOR AND RECORD. Access O2S11 (Front Bank 1) or O2S21 (Front Bank 2) PID. While observer views PID, test drive vehicle under different road conditions in an attempt to simulate original fault. If HO2S appears to switch properly, unable to duplicate problem. Go to next step. If HO2S does not appear to switch properly, replace HO2S. After repair, go to next step.

  21. Verify Trouble Shooting Of DTCs Completed

    Reconnect all disconnected 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 same DTC is not present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are present, trouble shooting is complete.
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