Re: P0423 Heated Catalyst Efficiency Below Threshold (Bank l)
OK, I've done some more research on this. This code is thrown when there is not enough difference between the Pre-Cat and Post-Cat sensors, ie it takes a measurement of the gasses before they enter the Cat, and then after to make sure the Cat is doing it's job.
If you get this error it means the Post-Cat sensor thinks too much O2 is getting past the Cat, this can be caused by a cracked manifold, a leaking manifold joint or the like.
But it can also happen if you do lots of short trips and the cat never gets up to temperature properly, the recommendation is there is a Secondary Air Injection Pump that is supposed to superheat the cat, maybe this is having issues?
Berb from the manual on the SAI pump:
The secondary air injection system is used to limit the emission of carbon monoxide (CO) and hydrocarbons (HC) that
are prevalent in the exhaust during cold starting of a spark ignition engine. The concentration of hydrocarbons
experienced during cold starting at low temperatures are particularly high until the engine and catalytic converter
reach normal operating temperature. The lower the cold start temperature, the greater the prevalence of
hydrocarbons emitted from the engine.
The SAI pump is used to provide a supply of air into the exhaust ports in the cylinder head, onto the back of the
exhaust valves, during the cold start period. The hot unburnt fuel particles leaving the combustion chamber mix with
the air injected into the exhaust ports and immediately combust. This subsequent combustion of the unburnt and
partially burnt CO and HC particles help to reduce the emission of these pollutants from the exhaust system. The
additional heat generated in the exhaust manifold also provides rapid heating of the exhaust system catalytic
converters. The additional oxygen which is delivered to the catalytic converters also generate an exothermic reaction
which causes the catalytic converters to 'light off' quickly.
The catalytic converters only start to provide effective treatment of emission pollutants when they reach an operating
temperature of approximately 25?C and need to be between temperatures of 40?C and 80?C
for optimum efficiency. Consequently, the heat produced by the secondary air injection “after burning”,
reduces the time delay before the catalysts reach an efficient operating temperature.
The engine control module (ECM) checks the engine coolant temperature when the engine is started, and if it is above
-9º C but below 50?C, the SAI pump is started. Secondary air injection will remain operational for a period controlled
by the ECM. The SAI pump operation can be cut short due to excessive engine speed or load.
Just some thoughts, I'm not massively clued up on how the emmisions system works on the L322, it's v advanced.
Dan