Catalyst Efficiency Monitor Malfunction

DTC P0420, P0430 DETECTION CONDITION AND POSSIBLE CAUSE

DTC P0420, P0430	CATALYST EFFICIENCY MONITOR MALFUNCTION
DETECTION CONDITION	P0420 indicates Bank 1 catalyst system efficiency is below acceptable threshold. P0430 indicates Bank 2 catalyst system efficiency is below acceptable threshold.
POSSIBLE CAUSE	Use of leaded fuel. Oil contamination. Cylinder misfiring. Damaged HO2S. Malfunctioning ECT sensor. Downstream HO2S wires improperly connected. High fuel pressure. Damaged exhaust system pipe. Damaged exhaust manifold. Damaged muffler/tailpipe assembly. Damaged catalytic converter. Retarded spark timing. NOTE: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that can produce higher than normal temperatures in the catalyst are particularly suspect, such as misfiring. Incorrect HO2S signal input (e. g., rich/lean signal when engine is operating under rich/lean conditions) can cause an abnormal temperature increase in the catalyst. ECT sensor DTCs can indicate that the thermostat is not operating correctly or that the engine coolant level is not filled to specification, producing above normal operating temperatures.
HINT	Refer to Catalyst Efficiency Monitor. See ENGINE OBD II MONITORS .
Courtesy of MAZDA MOTORS CORP.

DTC P0420, P0430 INSPECTION

STEP	INSPECTION		ACTION
1	NOTE: If entering this test from the symptom troubleshooting, go to next step. Was PCM Quick Test performed?	Yes	If any other DTC is recorded, go to appropriate DTC troubleshooting first. If only DTC P0420 and/or P0430 are recorded, go to next step.
1		No	Perform PCM Quick Test.
2	CHECK REAR HO2S WIRING AND PCM CONNECTIONS NOTE: If the electrical connections of the rear HO2S are interchanged/crossed, the Catalyst Efficiency Monitor Test will fail. Inspect the wiring of the rear HO2S for proper routing and connection. Disconnect the PCM and inspect for damaged/pushed out pins, corrosion and loose wires. Are there any concerns with the HO2S wiring or the PCM connection?	Yes	Repair any wiring or connection concerns. For PCM pin concerns, replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to step 10.
2		No	No Engine Control System related to DTCs or symptoms. Go to next step.
3	CHECK FUEL PRESSURE WARNING: The fuel system will remain pressurized when the engine is not running. To prevent injury or fire, use caution when working on the fuel system. NOTE: Fuel pressure above specification can produce abnormally rich air/fuel mixture. The rich air/fuel mixture can cause higher than normal catalyst operating temperatures. Key OFF. Install fuel pressure gauge. Start and run engine at idle. Record the fuel pressure. Increase engine speed to 2500 rpm and maintain for one minute. Record the fuel pressure. Is the fuel pressure 30-65 psi (207-448 kPa)?	Yes	Fuel pressure is OK. Remove fuel pressure gauge. Go to next step.
3		No	Fuel pressure is out of specification. See TEST 5: FUEL DELIVERY SYSTEM for diagnosis.
4	CHECK FOR OBVIOUS LEAK SOURCES IN THE EXHAUST SYSTEM NOTE: If a catalyst is in series with a leaking exhaust system, it can fail the Catalyst Efficiency Monitor test. Key OFF. Inspect the following for leaks, cracks, loose connections or punctures: Exhaust manifold. Front exhaust pipe. Rear exhaust pipe. Muffler/tailpipe assembly. Are the above components free of cracks and punctures, etc.?	Yes	Go to next step.
4		No	Repair the leak source(s). Go to step 10.
5	CHECK FOR OBVIOUS RESTRICTIONS IN THE EXHAUST SYSTEM Inspect the following for dents, areas of collapsed material and unusual bending: Front exhaust pipe. Rear exhaust pipe. Muffler/tailpipe assembly. Are the components free of dents and areas of collapsed material or unusual bending, etc.?	Yes	Go to next step.
5		No	Repair the restricted component(s) as necessary. Go to step 10.
6	CHECK MANIFOLD VACUUM FOR INDICATION OF EXCESSIVE EXHAUST SYSTEM RESTRICTION Attach a vacuum gauge to intake manifold vacuum source. Monitor RPM with NGS Tester or tachometer. Observe vacuum gauge needle while performing the following: NOTE: The vacuum gauge reading may be normal when the engine is first started and idled. However, excessive restriction in the exhaust system will cause the vacuum gauge needle to drop to a low point even while the engine is idled. Start the engine and gradually increase engine speed to 2, 000 RPM with the transmission in NEUTRAL. Decrease the engine to base idle rpm. Key OFF. Did manifold vacuum rise above 54 kPa (16 in-Hg) with the engine at 2000 rpm?	Yes	Go to next step.
6		No	Manifold vacuum did not reach an acceptable level. Go to step 8 to check for excessive restriction in the exhaust system.
7	CHECK MANIFOLD VACUUM FOR INDICATION OF MODERATE EXHAUST SYSTEM RESTRICTION Key ON, Engine Running (KOER). Increase engine speed gradually from base idle RPM to 2000 RPM with the transmission in NEUTRAL. Observe the rate of speed the vacuum gauge needle rises, while maintaining the increased engine rpm. NOTE: On a non-restricted exhaust system, the vacuum gauge needle will rise quickly to the normal range as the increased rpm is maintained. On a restricted exhaust system, the vacuum gauge needle will rise slowly to the normal range as the increased rpm is maintained. The rate of speed the vacuum gauge needle rises to the normal range is slower on a restricted system than on a non-restricted system as the increased rpm is maintained. Decrease engine speed to base idle rpm. Key OFF. Is the rate of speed that the vacuum gauge needle rises back to the normal range (above 54 kPa (16 in-Hg)) much slower than that of a non-restricted system?	Yes	A moderate restriction may be present. Go to next step.
7		No	No indications of restrictions or leaks have been detected in the exhaust system. If here because of DTCs P0420 or P0430, the catalytic converter is chemically inactive. Replace catalytic converter. Go to step 10.
8	CHECK MANIFOLD VACUUM WITH EXHAUST MANIFOLD DISCONNECTED FOR INDICATION OF A RESTRICTION NOTE: An intake manifold gasket leak can also cause the vacuum gauge needle to remain well below the normal range. Key OFF. Disconnect exhaust system immediately after the exhaust manifold. Repeat the vacuum measurement found in previous step. Did the vacuum needle QUICKLY rise above 54 kPa (16 in-Hg) with the engine rpm at 2000?	Yes	The exhaust system restriction is downstream of the exhaust manifold. Reconnect exhaust system at exhaust manifold. Go to next step.
8		No	A restriction is present in the exhaust manifold. Remove the vacuum gauge and tachometer. Inspect each exhaust port for casting flash/restrictions by dropping a length of chain into it. NOTE: Do not use a wire or lamp to check the ports. The restriction may be small enough for both to pass through, but large enough to cause excessive back-pressure at high engine rpm. Replace the exhaust manifold if unable to remove the casting flash/restriction. See EXHAUST MANIFOLD in 2.5L 4-Cylinder article in Engine for 2.5L engine. See EXHAUST MANIFOLD in 3.0L V6 article in Engine for 3.0L engine. See EXHAUST MANIFOLDS in 3.0L V6 article in Engine for 4.0L engine. Go to step 10.
9	CHECK MANIFOLD VACUUM WITH MUFFLER/TAILPIPE ASSEMBLY DISCONNECTED FOR INDICATION OF A RESTRICTION Key OFF. Disconnect muffler/tailpipe assembly located after catalytic converter. Repeat vacuum measurement found in step 7. Did the vacuum needle QUICKLY rise above 54 kPa (16 in-Hg) with the engine rpm at 2000?	Yes	There is a restriction in the muffler/tailpipe assembly. Replace the muffler/tailpipe assembly. Go to step 10.
9		No	There is a restriction in the catalytic converter. Remove the vacuum gauge and tachometer. Replace catalytic converter. Inspect the muffler to be certain converter debris has not entered. Go to step 10.
10	DRIVE CYCLE Make sure to reconnect all disconnected connectors. Clear DTCs from PCM memory using NGS tester generic OBD-II function. Perform Catalyst Monitor Drive Cycle. DRIVE CYCLES . Retrieve pending code. Is same DTC present?	Yes	Replace PCM. See COMPUTERIZED ENGINE CONTROLS . Go to next step.
10		No	Go to next step.
11	VERIFY TROUBLESHOOTING OF DTCs COMPLETED Perform PCM Quick Test. Is any DTC present?	Yes	Go to applicable DTC inspection.
11		No	Troubleshooting complete.