P0420 Catalyst system efficiency below threshold (Bank #1)
Catalyst Efficiency Monitor Steady StateThe Steady State Catalyst Efficiency Monitor is an on-board strategy designed to monitor and determine when a catalytic converter has fallen below the minimum level of effectiveness in its ability to control exhaust emissions. The monitor relies mainly on Heated Oxygen Sensors (HO2S) located downstream of the catalytic converter to infer catalyst efficiency based on oxygen storage capacity. The oxygen storage capacity of a high efficiency catalyst will have a slower downstream HO2S(s) switching frequency compared to the switching frequency of the upstream HO2S(s). As catalyst efficiency deteriorates, its ability to store oxygen declines causing the downstream HO2S(s) to switch more rapidly approaching the switching frequency of the upstream HO2S(s). The monitor uses this HO2S switching characteristic to evaluate the catalyst when the monitor is enabled. Input from the ECT, IAT, TP, CKP, and VSS sensors is required to enable the Catalyst Monitor. Also, a calibratable time must have elapsed since engine start up and operation in closed-loop fuel control. Once activated, closed-loop fuel control is temporarily transferred from the upstream HO2S(s) to the downstream HO2S(s). The monitor then analyzes the downstream HO2S signal switching frequency to determine if the catalytic converter has failed.
1. In the Steady State Catalyst Efficiency Monitor test, closed loop fuel control is transferred from the upstream HO2S(s) to the downstream HO2S(s). The switching frequency of the downstream HO2S(s) output is measured. This actual measured output frequency is called the test frequency. The test frequency is an indication of the oxygen storage capacity of the catalytic converter. The slower the test frequency, the higher the efficiency of the catalytic converter.
A second frequency called the calibrated frequency is calculated based on engine rpm and load. The calibrated frequency serves as a high limit threshold for the test frequency. If the test frequency is less than the calibrated frequency, the catalytic converter passes the Catalyst Efficiency Monitor test. If not, the catalytic converter or system is considered to have failed and a Diagnostic Trouble Code (DTC) is stored.
The DTCs associated with this test are DTCs P0420 and P0430.
2. The MIL is activated after a fault is detected on two consecutive drive cycles.
Catalyst Efficiency Monitor Federal Test Procedure - (All Except Probe)The Federal Test Procedure Catalyst Efficiency Monitor is an on-board strategy designed to monitor and determine when a catalytic converter has fallen below the minimum level of effectiveness in its ability to control exhaust emissions. It relies mainly on the front and rear Heated Oxygen Sensors (HO2S) to infer catalyst efficiency based upon oxygen storage capacity. The front and rear HO2S switches are counted under specified conditions for the purpose of calculating a rear to front HO2S switch ratio. After the switch ratio is calculated, it is compared against an emission threshold value. If the switch ratio is greater than the emission threshold, the catalyst has failed. The oxygen storage capacity of a high efficiency catalyst will have a low switch ratio and high HC efficiencies. As catalyst efficiency deteriorates, its ability to store oxygen declines and it will begin to have a higher switch ratio and low HC efficiencies. In general, as catalyst efficiency decreases, the switch ratio increases. Inputs from the ECT, IAT and TP sensors are required to enable the Federal Test Procedure Catalyst Monitor.
1. In the Federal Test Procedure Catalyst Efficiency Monitor test, only switches during steady state cruise conditions of a drive cycle are counted. Switches at idle or other drive modes are not counted. The counting of front and rear HO2S switches continues until a drive cycle is completed. At that time, the ratio of total rear switches to total front HO2S switches is calculated. If the switch ratio is greater than the emission threshold, the catalyst has failed and a Diagnostic Trouble Code (DTC) is stored.
The DTCs associated with this test are DTCs P0420 and P0430.
2. The MIL is activated after a fault is detected up to six consecutive drive cycles.
Catalyst Efficiency Monitor (Probe)The Catalyst Efficiency Monitor is an on-board strategy designed to monitor and determine when a catalytic converter has fallen below the minimum level of effectiveness in its ability to control exhaust emissions. It relies mainly on the front and rear Heated Oxygen Sensors (HO2S) to infer catalyst efficiency based upon oxygen storage capacity. The front and rear HO2S voltages are integrated under specified conditions for the purpose of calculating a rear to front HO2S voltage ratio. After the integrated voltage ratio is calculated, it is compared against a minimum emission threshold value for a "healthy" catalyst. If the rear to front integrated voltage ratio is less than the emission threshold, the catalyst has failed. As catalyst efficiency deteriorates, its ability to store oxygen declines and it will begin to have a lower rear to front integrated voltage ratio and low HC efficiencies. In general, as catalyst efficiency decreases, the integrated rear to front voltage ratio decreases. Inputs from the ECT, IAT and TP sensors are required to enable the Catalyst Monitor.
1. When the rear to front HO2S integrated voltage ratio is too low when compared to the emission threshold value for a deteriorated catalyst; the catalyst test fails.
The DTC associated with this test is DTC P0421.
2. The MIL is activated after three sequential failures of the catalyst efficiency test has been detected.
HF1 DTCs P0420, P0421, P0430 or P0431: CHECK FOR MISFIRE MONITOR DTCSDiagnostic Trouble Codes (DTC) P0420 and P0421 indicate that bank 1 catalyst system efficiency is below the acceptable threshold.
Diagnostic Trouble Codes (DTC) P0430 and P0431 indicate that bank 2 catalyst system efficiency is below the acceptable threshold.
NOTE 1: Complete the spark timing check in �«Quick Test�» before proceeding with this test step. Spark timing retarded below specification may increase exhaust gas temperature and decrease catalyst efficiency over time.
NOTE 2: Be sure customer has not:
(1) Refueled vehicle with leaded gasoline.
(2) Experienced high vehicle oil consumption.
NOTE 3: If entering this Pinpoint Test for symptoms only, go immediately to �«HF5�».
NOTE 4: Internal deterioration of a catalytic converter is usually caused by abnormal engine operation upstream of the catalyst. Events that may produce higher than normal temperatures in the catalyst are particularly suspect. For example, misfiring can cause higher than normal catalyst operating temperatures.
Possible causes:
-- Use of leaded fuel.
-- Oil contamination.
-- Cylinder misfiring.
-- Damaged HO2S.
-- Damaged ECT sensor.
-- Downstream HO2S wires improperly connected.
-- Fuel pressure too high.
-- Damaged exhaust system pipe.
-- Damaged exhaust manifold.
-- Damaged muffler/tail-pipe assembly.
-- Damaged catalytic converter.
l Key on, engine off.
l Retrieve and record all Continuous Memory DTCs (MIL and non-MIL).
l Were any of the following misfire monitor DTCs recorded: P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307 and P0308?
Yes
GO to Section 5A, �«Powertrain Diagnostic Trouble Code (DTC) Charts�», to address the misfire monitor DTCs.
No
GO to �«HF2�».
As your only CEL is a P420 the next step isWARNING:
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 pressures above specification may produce an abnormally rich air/fuel mixture. The rich air/fuel mixture may cause higher than normal catalyst operating temperatures.
l Key off.
l Inspect the vacuum hose going to the fuel pressure regulator for proper installation, cracks, etc. Service as necessary.
l Install fuel pressure gauge.
l Verify vacuum source to fuel pressure regulator.
l Start and run the engine at idle. Record the fuel pressure.
l Increase engine speed to 2500 rpm and maintain for one minute. Record the fuel pressure.
l Is the fuel pressure between 30 and 40 psi (210-310 kPa)?
yes the nest step is NOTE:
If a catalyst is in series with a leaking exhaust system, it can fail the Catalyst Efficiency Monitor test.
l Key off.
l Inspect the following for leaks, cracks, loose connections or punctures:
-- Exhaust manifold.
-- Front exhaust pipe.
-- Rear exhaust pipe.
-- Muffler/tail-pipe assembly.
l Are the above components free of cracks and punctures, etc.?
Yes
CHECK that the exhaust manifold to catalyst inlet pipe joint is tight. GO to �«HF8�».
No
REPLACE/REPAIR the leak source(s). COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, �«Powertrain Control Module (PCM) Reset�»). RERUN �«Quick Test�».
l Inspect the following for dents, areas of collapsed material and unusual bending:
-- Front exhaust pipe.
-- Rear exhaust pipe.
-- Muffler/tail-pipe assembly.
l Are the components free of dents and areas of collapsed material or unusual bending, etc.?
Yes
GO to �«HF9�».
No
REPLACE/REPAIR the restricted component(s) as necessary. COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, �«Powertrain Control Module (PCM) Reset�»). RERUN �«Quick Test�».
and the tests go on and on, but you get the idea......
