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Test Hf: Catalyst Efficiency Monitor & Exhaust Systems: Testing

NOTE: Proceed to DTC testing steps listed in FAULT CODE SETTING CONDITION  table of fault code setting condition.
FAULT CODE SETTING CONDITION

Fault Code KOEO KOER Continuous Memory
P0420      HF1
P0430      HF1
    NOTE: For additional testing information, see DIAGNOSTIC AIDS .
    NOTE: Ensure vehicle has not been re-fueled with leaded gasoline and that engine oil consumption has not increased. Engines that consume oil at a high rate will deposit high levels of phosphorus on catalyst and reduce catalyst efficiency.

  1. 1) For Continuous Memory Only DTC P0420 Or P0430: Check For Misfire Detection Monitor DTCs
    If directed to this test for symptoms only, go directly to step  5). DTC P0420 indicates Bank No. 1 catalyst system efficiency is below acceptable threshold. DTC P0430 indicates Bank No. 2 catalyst system efficiency is below acceptable threshold. Possible causes are:
    • Use Of Leaded Fuel
    • Faulty HO2S
    • Faulty ECT Sensor
    • High Fuel Pressure
    • Damaged Exhaust System Component
    • Oil Contamination
    • Cylinder Misfire
    • Downstream HO2S Sensor Improperly Connected
    • Retarded Spark Timing

    Retrieve all Continuous Memory DTCs (MIL or non-MIL). Check for misfire detection monitor DTCs P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0309, P0310, P0315, P0316 & P1309. If any misfire codes are present, diagnose those codes first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no misfire codes are present, go to next step.

  2. 2) Check For HO2S Monitor DTCs

    Incorrect HO2S signal input (such as a rich or a lean input signal when engine is operating under a lean or a rich condition) can cause an abnormal temperature increase in catalyst. For possible HO2S monitor DTCs, see HEATED OXYGEN SENSOR MONITOR under DIAGNOSTIC MONITORS. If any of these DTCs are present, perform appropriate system test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If none of these DTCs were present, go to next step.
    3. NOTE: ECT or CHT sensor DTCs can indicate thermostat is not operating correctly or engine coolant level is not filled to specification, possibly causing higher than normal operating temperatures.

  3. 3) Check For ECT Or CHT Sensor DTCs
    If DTC P0117, P0118, P0125, P0128, P1117, P1285, P1288, P1289, P1290 or P1299 was present in step 1)  , perform appropriate system test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If none of these DTCs are present in step 1)  , go to next step.

  4. 4) Check For Any Other DTCs

    If any other DTCs are present in step 1)  (not including initial DTC P0420 and P0430), perform appropriate system test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If only DTC P0420 and/or P0430 are present in step 1)  , go to next step.
    5. NOTE: If electrical connections of rear HO2S are interchanged or crossed, Catalyst Efficiency Monitor Test will fail.

  5. 5) Check Rear HO2S Wiring & PCM Connections
    Turn ignition switch to OFF position. Ensure HO2S wiring harness is correctly routed, wires are not crossed and connectors are tight. Repair as necessary. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Check PCM terminals. If PCM terminals are damaged, replace PCM. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If wiring harness, connectors and terminals are okay, go to next step.
    6. WARNING: Always refer to safety procedures to reduce possibility of injury. See FUEL SYSTEM SAFETY PRECAUTIONS .
    NOTE: Fuel pressures above specification can produce an abnormally rich air/fuel mixture, causing higher than normal catalyst operating temperatures.

  6. 6) Check Fuel Pressure
    Turn ignition switch to OFF position. Release fuel pressure. See FUEL SYSTEM PRESSURE RELEASE procedure under FUEL SYSTEMS in appropriate REMOVAL & INSTALLATION article. Perform the following checks for appropriate fuel system:

    • Returnable Fuel Systems

      Inspect vacuum hose going to fuel pressure regulator for proper installation and cracks. Repair as necessary. Verify vacuum source to fuel pressure regulator is okay.

    • Mechanical Returnless Fuel Systems (MRFS)

      If applicable, inspect vacuum hose going to fuel rail pulse damper for proper installation and cracks. Repair as necessary.

    Connect scan tool to Data Link Connector (DLC). On vehicles with Electronic Returnless Fuel Systems (ERFS), monitor fuel pressure by selecting FRP PID from PID/DATA MONITOR & RECORD menu. On all others, install fuel pressure gauge to Schrader valve on fuel rail. On all models, start engine and allow to idle. Record FRP PID value or fuel pressure gauge reading at idle. Increase engine speed and hold at 2500 RPM for one minute. Record FRP PID value or fuel pressure gauge reading with engine speed increased. Compare fuel pressure readings with fuel system pressure specifications. See FUEL PRESSURE SPECIFICATIONS . If fuel pressure is within specification, remove fuel pressure gauge (if applicable) and go to next step. If fuel pressure is not within specification, go to TEST HC, step  4).

    7. NOTE: If a catalyst is in series with a leaking exhaust system, it can fail Catalyst Efficiency Monitor test.

  7. 7) Check For Obvious Leak Sources In Exhaust System
    Inspect complete exhaust system from exhaust manifold to tailpipe for leaks, cracks, loose connections or punctures. Repair as necessary. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If exhaust system is okay, go to next step.
    8. NOTE: A slight pressure in exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation. Causes of high exhaust back pressure are dents or obstructions in exhaust pipe, or a plugged catalytic converter or muffler.

  8. 8) Check For Obvious Restrictions In Exhaust System
    Inspect complete exhaust system for collapsed areas, dents or excessive bends. Repair or replace as necessary. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If exhaust system is okay, go to next step.
    9. NOTE: If an exhaust back pressure tester is not available, go to step  10).

  9. 9) Check For Excessive Exhaust Back Pressure
    Install an exhaust back pressure tester and follow tool manufacturer's installation and testing instructions (if available). Exhaust back pressure when measured near exhaust manifold and at normal engine operating temperature should not exceed 3 psi (20.7 kPa) at idle, and 8 psi (55.2 kPa) at wide open throttle under load. If exhaust back pressure test indicates a restriction, repair restricted component(s) as necessary. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. For further diagnosis of LACK OF POWER, LOSS OF POWER, or NO START symptom, return to SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article. If exhaust back pressure test does not indicate a restriction and you were directed here for DTCs P0420 or P0430, catalytic converter is chemically inactive. Replace catalytic converter. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If directed here for LACK OF POWER, LOSS OF POWER, or NO START symptom, return to SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article for further testing.
    10. NOTE: Vacuum gauge reading may be normal when engine is first started and idling. However, excessive restriction in exhaust system will cause intake manifold vacuum to decrease with engine at a steady or constant idle speed.

  10. 10) Check Manifold Vacuum For Indication Of Excessive Exhaust System Restriction
    Install tachometer. Connect vacuum gauge to intake manifold vacuum source. Place transmission in Neutral. Start engine and gradually raise engine speed to 2000 RPM. Manifold vacuum reading should increase to more than 16 in. Hg (54 kPa). Allow engine speed to return to idle. Turn ignition switch to OFF position. If manifold vacuum reading was as specified, go to next step. If manifold vacuum reading did not reach specified level, go to step  12) to check for excessive exhaust system restriction.

  11. 11) Check Manifold Vacuum For Indication Of Moderate Exhaust System Restriction

    Leave transmission in Neutral and tachometer and vacuum gauge connected. With engine still idling, gradually raise engine speed to 2000 RPM. Observe vacuum gauge reading response while maintaining increased engine RPM. If an exhaust system is free of restrictions, manifold vacuum increases quickly to 16 in. Hg (54 kPa) as increased RPM is maintained. If exhaust system is restricted, manifold vacuum increases slowly to 16 in. Hg (54 kPa) as increased RPM is maintained. If manifold vacuum is slow to raise to 16 in. Hg (54 kPa), go to next step to check for a moderate restriction. If manifold vacuum is okay, no indication of exhaust leak or restriction has been detected. If directed here for DTCs P0420 or P0430, catalytic converter is chemically inactive. Replace catalytic converter. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If directed here for LACK OF POWER, LOSS OF POWER, or NO START symptom, return to SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article for further testing.
    12. NOTE: An intake manifold gasket leak can cause vacuum gauge reading to remain below normal range.

  12. 12) Check Manifold Vacuum With Exhaust System Disconnected From Exhaust Manifold
    Leave tachometer and vacuum gauge connected. Disconnect exhaust pipe from exhaust manifold. Start engine and gradually raise engine speed to 2000 RPM. Observe vacuum gauge reading response while maintaining increased engine RPM. If manifold vacuum is okay, exhaust restriction is downstream of exhaust manifold. Reconnect exhaust system to exhaust manifold and go to next step. If manifold vacuum is low or slow to respond, restriction is present in exhaust manifold. Check exhaust manifold for restrictions. If restrictions are present and are unable to be removed, replace exhaust manifold. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair.

  13. 13) Check Manifold Vacuum With Muffler & Tailpipe Assembly Disconnected

    Leave tachometer and vacuum gauge connected. Disconnect muffler and tailpipe assembly from rear of catalytic converter. Start engine and gradually raise engine speed to 2000 RPM. Observe vacuum gauge reading response while maintaining increased engine RPM. If manifold vacuum is now okay, fault is in muffler and tailpipe assembly. Repair as necessary. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair. If manifold vacuum is still not okay, fault is in catalytic converter. Replace catalytic converter. After replacing catalytic converter, check muffler and tailpipe assembly for debris from faulty catalytic converter. Perform DRIVE CYCLES . Ensure CATALYST MONITOR PROCEDURE is performed to verify repair.
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