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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 69 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0420 Or DTC P0430 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Mazda Tribute. However, it is still accessible from the selected car via links, so may be relevant.
  1. If entering this test from Symptom Trouble Shooting, go to next step. IF QUICK TEST was not performed, go to QUICK TEST  under SELF-DIAGNOSTIC SYSTEM. If QUICK TEST was performed and any other DTCs are present, go to applicable procedure for other DTCs first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If only DTC P0420 and/or P0430 are present, go to next step.
    2. NOTE: If electrical connections of rear HO2S are interchanged/crossed, Catalyst Efficiency Monitor Test will fail.
  2. Check Rear HO2S Wiring & PCM Connections -  Inspect wiring of rear HO2S for proper routing and connection. Disconnect PCM 104-pin harness connector, inspect for damaged or pushed out pins, corrosion and loose wires. If any wiring or connection problems are present, repair as necessary. After repair, go to step  10. If faulty terminals at PCM are present, replace PCM. After repair, go to step  10. If no faults are present related to DTCs, go to next step.
    3. WARNING: Fuel system will remain pressurized when engine is not running. To prevent injury or fire, use caution when working on fuel system.
    NOTE: Fuel pressures above specification can produce abnormally rich air/fuel mixture. Rich air/fuel mixture can cause higher than normal catalyst operating temperatures.
  3. Check Fuel Pressure -  Turn ignition off. Install fuel pressure gauge. Start and run engine at idle. Record fuel pressure. Increase engine speed to 2500 RPM and maintain for one minute. Record fuel pressure. If fuel pressure is 55-70 psi (380-482 kPa), go to next step. If fuel pressure is not as specified, refer to FUEL DELIVERY SYSTEM  testing under SYSTEM TESTS.
    4. NOTE: If a catalyst is in series with a leaking exhaust system, it can fail Catalyst Efficiency Monitor test.
  4. Check For Obvious Leak Sources In Exhaust System -  Turn ignition off. Inspect following for leaks, cracks, loose connections or punctures:
    • Exhaust manifold.
    • Front exhaust pipe.
    • Rear exhaust pipe.
    • Muffler/tailpipe assembly.

    If components are free of cracks and punctures, etc., go to next step. If components are not free of cracks or punctures, repair source of fault as necessary. After repair, go to step  10.

  5. Check For Obvious Restrictions In The Exhaust System -  Inspect following for dents, areas of collapsed material and unusual bending:
    • Front exhaust pipe.
    • Rear exhaust pipe.
    • Muffler/tailpipe assembly.
    If components are free of dents and areas of collapsed material or unusual bending, etc., go to next step. If components are not free of dents and areas of collapsed material or unusual bending, etc., repair or replace restricted components as necessary. After repair, go to step  10.
    6. NOTE: Vacuum gauge reading may be normal when engine is first started and idled. However, excessive restriction in exhaust system will cause vacuum gauge needle to drop to a low point even while engine is idled.
  6. Check Manifold Vacuum For Indication Of Excessive Exhaust System Restriction -  Attach vacuum gauge to intake manifold vacuum source. Monitor RPM with scan tool or tachometer. Observe vacuum gauge needle while performing following:
    • Start engine and gradually increase engine speed to 2000 RPM with transaxle in neutral.
    • Decrease engine speed to base idle RPM.
    Turn ignition off. If manifold vacuum increased to more than 16 in. Hg (54 kPa) with engine at 2000 RPM, go to next step. If manifold vacuum did not increase as specified, go to step  8.
    7. NOTE: On a non-restricted exhaust system, vacuum gauge needle will rise quickly to more than 16 in. Hg (54 kPa) (normal range) as increased RPM is maintained. On a restricted exhaust system, vacuum gauge needle will rise slowly to normal range as increased RPM is maintained.
  7. Check Manifold Vacuum For Indication Of Moderate Exhaust System Restriction -  Start engine. Increase engine speed gradually from base idle RPM to 2000 RPM with transaxle in neutral. Observe rate of speed vacuum gauge needle rises, while maintaining increased engine RPM. Decrease engine speed to base idle RPM. Turn ignition off. If rate of speed that vacuum gauge needle returned back to normal range was much slower than that of a non-restricted system, go to next step. If rate of speed that vacuum gauge needle returned back to normal range was same as that of a non-restricted system, no fault is present. If here because of DTCs P0420 or P0430, catalytic converter is chemically inactive. Replace catalytic converter. After repair, go to step  10.
    8. NOTE: An intake manifold gasket leak can also cause vacuum gauge needle to remain well below normal range.
    NOTE: In following step, do not use a wire or lamp to check ports. Restriction may be small enough for both to pass through, but large enough to cause excessive back-pressure at high engine RPM.
  8. Check Manifold Vacuum With Exhaust Manifold Disconnected For Indication Of A Restriction -  Turn ignition off. Disconnect exhaust system immediately after exhaust manifold. Repeat vacuum measurement performed in step  7. If vacuum needle quickly rose to more than 16 in. Hg (54 kPa) with engine speed at 2000 RPM, exhaust restriction is down stream of exhaust manifold. Reconnect exhaust system. Go to next step. If vacuum needle did not rise quickly to more than 16 in. Hg (54 kPa) with engine speed at 2000 RPM, a restriction is present in exhaust manifold. Remove vacuum gauge and tachometer. Inspect exhaust manifold for casting flash/restrictions by dropping length of chain into it. Replace exhaust manifold if unable to remove casting flash/restriction. After repair, go to step  10.
  9. Check Manifold Vacuum With Muffler/Tailpipe Assembly Disconnected For Indication Of A Restriction -  Turn ignition off. Disconnect muffler/tailpipe assembly located after catalytic converter. Repeat vacuum measurement performed in step  7. If vacuum needle quickly rose to more than 16 in. Hg (54 kPa) with engine speed at 2000 RPM, restriction is in muffler and tailpipe. Replace muffler and tail pipe. After repair, go to next step. If vacuum needle did not rise quickly to more than 16 in. Hg (54 kPa) with engine speed at 2000 RPM, restriction is in catalytic converter. Remove vacuum gauge and tachometer. Replace catalytic converter. Ensure converter debris did not enter muffler. After repair, go to next step.
  10. Drive Cycle -  Reconnect all disconnected connectors. Clear DTCs from PCM memory using scan tool generic OBD-II function. Perform Catalyst Monitor Repair Verification Drive Cycle. Refer to MONITOR REPAIR VERIFICATION DRIVE CYCLES  under DRIVE CYCLE PROCEDURES. Retrieve pending code. If same DTC is present, replace PCM. After repair, go to next step. If same DTC is not set, go to next step.
  11. Verify Trouble Shooting Of DTCs Completed -  Perform PCM Quick Test. If any DTC is present, go to applicable procedure for other DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are set, trouble shooting is complete.
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