DTC P0420 [YF (2.0L Zetec)]

DTC P0420	Catalyst system efficiency below threshold
DETECTION CONDITION	• The PCM monitors catalyst converter efficiency using HO2S-11 and HO2S-12 switch rate. If the PCM detects that HO2S-12 signal begins to switch more rapidly with increase amplitude, approaching the switching rate and amplitude of HO2S-11, the PCM determines the catalyst converter efficiency below threshold.
POSSIBLE CAUSE	• Leaded fuel is used • Damaged HO2S-11 and/or HO2S-12 • Damaged cylinder head temperature sensor • Excessive fuel pressure • Damaged exhaust manifold • Damaged catalyst converter • Oil contamination • Misfire is occurring at cylinder • HO2S-12 wiring harness connection improper • Damaged exhaust system pipe • Damaged muffler/tail pipe assembly • Ignition timing retarded


STEP	INSPECTION		ACTION
1	VERIFY FREEZE FRAME DATA HAS BEEN RECORDED • Has FREEZE FRAME DATA been recorded?	Yes	Go to the next step.
1		No	Record the FREEZE FRAME DATA on the repair order, then go to the next step.
2	VERIFY REPAIR INFORMATION AVAILABILITY • Verify related service repair information availability. • Is any related repair information available?	Yes	Perform repair or diagnosis according to the available repair information. If the vehicle is not repaired, go to the next step.
2		No	Go to the next step.
3	CHECK FOR MISFIRE DETECTION MONITOR DTCS Note • Be sure customer has not: - Refueled vehicle with leaded gasoline. - Noticed high vehicle oil consumption. • If entering this Pinpoint Test for symptoms only, immediately go to Step 7. • Internal deterioration of catalytic converter usually caused by abnormal engine operation upstream of catalyst. • Events that can produce higher than normal temperature in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst opening temperatures. • Retrieve any of the following Misfire Detection Monitor DTCs (MIL and non-MIL). • Were any of the Misfire Detection Monitor DTCs (P0300, P0301, P0302, P0303 or P0304) detected?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
3		No	Go to the next step.
4	CHECK FOR HO2S MONITOR DTCS Note • Incorrect HO2S signal input (such as rich/lean input signal when the engine is operating under lean/rich conditions) can cause an abnormal temperature increase in the catalyst. • Were any of the following HO2S monitor DTCs recorded in Step 3: P0136, P0138 and P0141?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
4		No	Go to the next step.
5	CHECK FOR CYLINDER HEAD TEMPERATURE OR CHT SENSOR DTCS Note • The cylinder head temperature sensor DTCs can indicate that the thermostat is not operating correctly or that the engine coolant level is no-filled to specification, producing above normal operating temperatures. • Were any of the following cylinder head temperature sensor DTCs recorded in Step 3: P0117, P0118, P0125, P1117 and P1299?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
5		No	Go to the next step.
6	INDETIFY TRIGGER DTC FOR FREEZE FRAME DATA • Is DTC P0420 on FREEZE FRAME DATA?	Yes	Go to the next step.
6		No	Go to FREEZE FRAME DATA DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
7	CHECK HO2S-12 WIRING AND PCM CONNECTIONS Note • If the electrical connections of the HO2S are integrated/crossed, the Catalyst Efficiency Monitor Test will fall. • Inspect the wiring of HO2S-12 for proper routing and connection. • Disconnect the PCM, inspect for damaged pushed out pins, corrosion and loose wires. • Are there any concerns with the HO2S-12 wiring or the PCM connection?	Yes	Repair or replace malfunctioning part. If PCM connector terminal concerns, replace the PCM. Then go to Step 15.
7		No	Go to the next step.
8	CHECK FUEL PRESSURE Note • Fuel pressures above specification can produce an abnormally rich air/fuel mixture. The rich air/fuel mixture can cause higher than normal catalyst operating temperatures. • If applicable, inspect the vacuum hose going to the fuel rail pulsation damper for proper installation and cracks. Repair as necessary. • Install the pressure gauge. • Start and run the engine at idle. Record the fuel pressure. • Measure the fuel pressure, after increase the engine speed to 2,500 rpm and maintain for 1 minute. • Was the fuel pressure within the specifications?	Yes	Go to the next step.
8		No	Repair or replace malfunctioning part according to inspection results, then go to Step 15.
9	CHECK FOR OBVIOUS LEAK SOURCES IN EXHAUST SYSTEM Note • If a catalyst is in series with a leaking exhaust system, It can fail the Catalyst Efficiency Monitor test. • Inspect the following in 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 the next step.
9		No	Repair the leak sources. Then go to Step 15.
10	CHECK FOR OBVIOUS RESTRICTIONS IN EXHAUST SYSTEM • Inspect the following in 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 the next step.
10		No	Repair or replace the restricted component (s), then go to Step 15.
11	CHECK MANIFOLD VACUUM FOR INDICATION OF EXCESSIVE EXHAUST SYSTEM RESTRICTION • Attach a vacuum gauge to the intake manifold vacuum source. • Connect the WDS or equivalent to DLC-2. • Turn the ignition switch to ON. • Access RPM PID. Note • The vacuum gauge reading may be normal when the engine is first started and idling. However, excessive restriction in the exhaust system will cause intake manifold vacuum to decrease with the engine at a steady/constant idle speed. • Observe the vacuum gauge needle while completing the following: - Start the engine and gradually increase the engine speed to 2,000 rpm with the transaxle in NEUTRAL. • Decrease engine speed to base idle speed. • Turn the ignition switch to OFF. • Did manifold vacuum rise above 54 kPa {16 inHg} with the engine speed at 2,000 rpm?	Yes	Go to the next step.
11		No	Go to Step 13 to check for excessive restriction in the exhaust system.
12	CHECK MANIFOLD VACUUM OR INDICATION OF MODERATE EXHAUST SYSTEM RESTRICTION • Start the engine run it at idle. • Increase the engine speed gradually from base engine rpm to 2,000 rpm with the transaxle in NEUTRAL. • Observe the 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 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. • Turn the ignition switch to OFF. • Is the rate of speed that the vacuum gauge needle rise back to the normal range (above 54 kPa {16 inHg}) much slower than that of a non-restricted system?	Yes	Go to the next step.
12		No	No indications of restrictions or leak have been detected in the exhaust system. Replace catalytic converter, then go to Step 15.
13	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 maintain well below the normal range. • Disconnect exhaust system immediately after the exhaust manifold. • Go to Step 12 and repeat the vacuum measurement. • Did the vacuum needle quickly rise above 54 kPa {16 inHg} with the engine speed at 2,000 rpm?	Yes	The exhaust system restriction is downstream of the exhaust manifold. Go to the next step.
13		No	Replace the exhaust manifold, then go to Step 15.
14	CHECK MANIFOLD VACUUM WITH MUFFLER/TAIL PIPE ASSEMBLY DISCONNECTED FOR INDICATION OF A RESTRICTION • Disconnect muffler/tailpipe assembly from the catalytic converter. • Go to Step 12 and repeat the vacuum measurement. • Did the vacuum needle quickly rise above 54 kPa {16 inHg} with the engine speed at 2,000 rpm?	Yes	Replace muffler/tailpipe assembly, then go to the next step.
14		No	Replace catalytic converter, then go to the next step.
15	VERIFY TROUBLESHOOTING OF DTC P0420 COMPLETED • Make sure to reconnect all disconnected connectors. • Clear the DTC from the PCM memory using the WDS or equivalent. • Drive the vehicle in stop-and-go traffic conditions. Include five different constant cruise speeds, ranging 40-72 km/h {25-45 MPH} over a 10 minutes period. • Is the PENDING CODE same DTC present?	Yes	Replace PCM, then go to the next step. (See PCM REMOVAL/INSTALLATION [YF (2.0L Zetec)].)
15		No	Go to the next step.
16	VERIFY AFTER REPAIR PROCEDURE • Perform "After Repair Procedure". (See AFTER REPAIR PROCEDURE [YF (2.0L Zetec)].) • Is there any DTC present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [YF (2.0L Zetec)].)
16		No	Troubleshooting completed.