Question about 2005 Ford Focus
I looked up the code p0420,------- the catalyst system efficiency below threshold (cylinder bank #1).Try changing the oxygen sensor, the one by the cat converter first. Yes it is true, the cat and the manifold is all one unit, but try the sensor first,it's cheaper.
Posted on Mar 12, 2009
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Posted on Jan 02, 2017
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code PO420 you have is Catalyst System efficiency is below threshold bank one.
Usually replacing the O2 sensor that's the front most in the exhaust system
will cure your problem,
Your Check Engine light
is on and you find a P0420 code for a catalytic converter fault. Does that really
mean your converter has reached the end of the road and needs to be replaced? A
new converter can cost $600 to $1000 or more if a new car dealer or repair shop does the
job, or maybe half that amount if you do it yourself. It's an expensive fix
that may or may not be necessary. The problem, in most cases, is an emissions
issue, not a performance issue that affects the way the engine runs.
A P0420 diagnostic
trouble code is a "generic" fault code that is set when the Onboard Diagnostic II
(OBD II) system sees a drop in converter efficiency. The
OBD II system monitors catalyst efficiency by comparing the switching activity
of the upstream and downstream oxygen sensors in the exhaust. The upstream O2
sensor in theexhaust manifold reflects the
condition of the exhaust gases as they exit the engine. The downstream O2
sensor in or behind the catalytic converter reflects the condition of the
exhaust after it passes through he converter.
The catalytic converter
is like an after-burner. It oxidizes (burns) any residual fuel vapors (unburned
hydrocarbons or HC) in the exhaust. It also burns any carbon monoxide (CO) in
the exhaust. The exhaust must meet federal emission standards, and if a problem
exists that causes emissions to exceed the federal limits by 150%, the OBD II
system is supposed to catch the fault, set a code and turn on the Check Engine
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