Diagnostic trouble code P0420.

Diagnostic trouble code P0420.

Catalyst System Efficiency Below Threshold (Bank 1)

Diagnostic trouble code P0420 what it means and what to check.

2001 Nissan Altima with 2.4 liter 4 cylinder engine customer concern check engine light is illuminated. The vehicle bogs down on sudden acceleration no power on take off.
A catalytic convertor cleans up the pollutants left over from combustion namely hydrocarbons (HC) and carbon monoxide (CO) to low levels.

Initial checks coolant and oxygen sensors for proper operation. A thermostat that is stuck in open position or a defective positive crankcase ventilation valve. A defective fuel pressure regulator or a bad injector misfiring cylinders can cause un burnt fuel to enter the catalytic converter which could lead to failure.

Catalytic converter

Diagnostic trouble code P0420. First step is to scan test and check the oxygen sensors for switching B1 sensor 1 should be switching from rich to lean. The B2 oxygen sensor should not be switching and stay steady . The second test is to remove the oxygen sensor on the manifold and attach a back pressure gauge by means of an adaptor. The readings should be 0 to .5 at idle and should not go above 1.25 psi at 2500 rpm.
A bad catalytic converter can decrease gas mileage and loss of power and in some cases cause engine failure. A good catalytic converter that is functioning normally does not have a restriction and lets the exhaust gas flow freely. When the temperature exceeds the specified limits the honey comb inside the catalytic converter could melt and cause restriction.
Periodic preventive maintenance such as regular oil change, cooling system flush and inspection of ignition and fuel system components can increase the life of an engine.

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