Catalyst Efficiency Monitor Malfunction

DTC DETECTION CONDITION POSSIBLE COUSES CHART

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 CAUSES	Use of leaded fuel Oil contamination Cylinder misfiring Damaged HO2S Malfunctioning ECT/CHT sensor Downstream HO2S wires incorrectly connected Fuel pressure too high 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/CHT 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	See catalyst efficiency monitor. See DOWNSTREAM HEATED OXYGEN SENSOR (HO2S) .

DTC DETECTION CONDITION POSSIBLE COUSES CHART

STEP	INSPECTION		ACTION
1	PCM QUICK TEST NOTE: If entering this test from the symptom troubleshooting, GO to the next step. 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. For example, misfiring can cause higher than normal catalyst operating temperatures. NOTE: Make sure the customer has not: refueled the vehicle with leaded gasoline. noticed a high vehicle oil consumption. An engine that consumes oil at a high rate deposits high levels of phosphorus on the catalyst and reduces the catalyst efficiency. Was the PCM Quick Test carried out?	Yes	If any other DTC is recorded, go to appropriate DTC troubleshooting information first. If only DTC P0420 and/or P0430 are recorded, GO to the next step.
1		No	CARRY OUT the PCM Quick Test. See PCM QUICK TEST .
2	CHECK THE ELECTRONIC ENGINE CONTROL (EEC) WIRING HARNESS NOTE: Check the HO2S electrical connectors to make sure the correct HO2S is connected to the correct electrical connector. The electrical connectors are color coded to make sure the correct connection is made. NOTE: If the electrical connections of the rear HO2S are interchanged/crossed, the Catalyst Efficiency Monitor Test will fail. Visually inspect the HO2S harness connectors for any indication of crossed wiring. Visually inspect the harness for exposed wiring, corrosion and correct routing. Visually inspect the PCM connectors for damaged, or pushed out pins, corrosion and loose wires. Are there any concerns with the wiring or the PCM connection?	Yes	REPAIR as necessary. CLEAR the DTCs. CARRY OUT the catalyst monitor drive cycle to verify the repairs.
2		No	GO to the next step.
3	CHECK FUEL PRESSURE WARNING: The fuel system remains pressurized when the engine is not running. To prevent injury or fire, use caution when working on the fuel system. Refer to the fuel system WARNING information at the beginning of Test 4. See TEST 4: FUEL DELIVERY SYSTEM . Failure to follow these instructions may result in personal injury. NOTE: Fuel pressures above specification can produce abnormally rich air/fuel mixture. The rich air/fuel mixture can cause higher than normal catalyst operating temperatures. NOTE: Fuel pressure for MRFS (2) system should read between 262-448 (kPa) and 38-65 (psi). Mechanical returnless fuel systems (MRFS): If applicable, inspect the vacuum hose going to the fuel rail pulse damper for correct installation and cracks. Repair as necessary. Install fuel pressure gauge. Start and run engine at idle. Record the fuel pressure. Compare the recorded fuel pressure reading to the fuel system specification found at the beginning of this pinpoint test step. Key OFF. Is the fuel pressure within specifications?	Yes	Fuel pressure is OK. REMOVE fuel pressure gauge. GO to the next step.
3		No	Fuel pressure is out of specification. See TEST 4: FUEL DELIVERY SYSTEM for diagnosis.
4	CHECK FOR LEAKS IN THE EXHAUST SYSTEM NOTE: If a catalyst is in series with a leaking exhaust system, it can fail the Catalyst Efficiency Monitor Test. Inspect the exhaust system for leaks, cracks, loose connections, punctures, or non-factory modifications. Is a concern present?	Yes	REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test. CARRY OUT the catalyst monitor drive cycle to verify the repairs.
4		No	REPAIR as necessary. GO to step 9.
5	CHECK FOR RESTRICTIONS IN THE EXHAUST SYSTEM NOTE: A slight pressure in the exhaust system is normal, but excessive exhaust back pressure seriously affects engine operation. Inspect the following for damage or restrictions: Front and rear exhaust pipes Catalytic converter Muffler/tailpipe assembly Is a concern present?	Yes	REPAIR as necessary. CLEAR the DTCs. REPEAT the self-test.
5		No	GO to the next step.
6	CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE The internal condition of an exhaust system and its ability to flow can be checked within an exhaust back pressure tool. Is an exhaust back pressure tester available?	Yes	GO to the next step.
6		No	GO to step 8.
7	CHECK FOR EXCESSIVE EXHAUST BACK PRESSURE WITH EXHAUST BACK PRESSURE TOOL NOTE: Typical exhaust back pressure, when measured near the exhaust manifold and at normal engine operating temperature, should not exceed 20.7 kPa (3 psi) at idle and 55.2 kPa (8 psi) at wide open throttle (WOT) under load. Install an exhaust back pressure tester and follow the tool manufacturers installation and testing instructions. Does the exhaust back pressure test indicate a restriction?	Yes	REPAIR the restricted component(s) as necessary. To continue diagnosis of a symptom (lack of power, loss of power or no start), see DIAGNOSTIC INDEX . GO to step 9.
7		No	No indication of restrictions or leaks has been detected in the exhaust system. To continue diagnosis of a symptom (lack of power, loss of power or no start), see DIAGNOSTIC INDEX to check for excessive restriction in the exhaust system.
8	CHECK MANIFOLD VACUUM FOR AN INDICATION OF EXCESSIVE EXHAUST SYSTEM RESTRICTION NOTE: When the engine is first started and is idled, the reading may be normal 51-74 kPa (15-22 in-Hg), but as the engine RPM is increased, the back pressure caused by a clogged exhaust system caused the needle to slowly drop to 0 kPa (0 in-Hg). The needle then may slowly rise. Excessive exhaust restriction causes the needle to drop to a low point even if the engine is only idling. Attach a vacuum gage to the intake manifold vacuum source. Observe the vacuum gauge while increasing the engine RPM. Does the vacuum gauge indicate an exhaust restriction concern?	Yes	REPAIR the restricted component(s) as necessary. To continue diagnosis of a symptom (lack of power, loss of power or no start), see DIAGNOSTIC INDEX . GO to step 9.
8		No	No indication of restrictions or leaks has been detected in the exhaust system. To continue diagnosis of a symptom (lack of power, loss of power or no start), see DIAGNOSTIC INDEX to CHECK for excessive restriction in the exhaust system.
9	CARRY OUT THE CATALYST MONITOR DRIVE CYCLE Carry out the Catalyst Monitor Drive Cycle. See ON BOARD DIAGNOSTIC (OBD) DRIVE CYCLE . Retrieve pending code. Is DTC P0420 or P0430 present?	Yes	INSTALL a new catalyst between the monitored HO2S sensors, only for the bank referenced, (P0420 Bank 1), (P0430 Bank 2). Do not install a new unmonitored catalyst unless it is repaired as an assembly. See EXHAUST SYSTEM - 2.5L or EXHAUST SYSTEM - 3.0L . CLEAR the DTCs. REPEAT the self-test.
9		No	The test is complete and no concerns are present.