The check engine light recently came on on my 2002 Astro van - 4.3L engine - 2WD with 151km. Had a recent tune-up (plugs, wires, rotor, etc.), And also included replacing the fuel pressure regulator to solve a slow starting problem. The code shown is: P0420 – Catalyst System Efficiency Below Threshold (Bank 1)
Any suggestion on what the possible cause and repair might be. Thanks
Fouling, clogging, melt-down and breakage of the ceramic substrate inside a converter are common conditions that can cause problems. Plugging is usually the end result of a melt-down, which occurs because the converter gets too hot. This happens because the engine is dumping unburned fuel into the exhaust. The excess fuel lights off inside the converter and sends temperatures soaring. If it gets hot enough, the ceramic substrate that carries the catalyst melts.
The unburned fuel may be getting into the exhaust because of a bad spark plug or valve, but an overly rich air/fuel mixture is another possibility. In older carbureted engines, a heavy or misadjusted carburetor float may be the underlying cause. But on newer engines with "feedback" carburetion or electronic fuel injection, the engine may not be going into "closed loop" (the normal mode where the computer regulates the air/fuel mixture to minimize emissions).
A bad oxygen sensor or coolant sensor may be giving the computer bogus information. A sluggish or dead O2 sensor will make the computer think the exhaust is running lean, so the computer will try to compensate by making the fuel mixture rich. A coolant sensor that always indicates a cold engine will also keep the system in open loop, which means a steady diet of excess fuel. But it might not be the sensor s fault. A thermostat that s stuck open or is too cold for the application can prevent the engine from reaching its normal operating temperature. So if your converter has failed and needs to be replaced, the engine should be diagnosed for any underlying problems before the new converter is installed.
Another cause of converter clogging and contamination is excessive oil consumption. Worn valve guides or seals can allow oil to be sucked into the engine s combustion chambers. The same goes for worn or damaged rings or cylinders. Oil can form a great deal of carbon, and metals present in the oil can contaminate the catalyst. A compression check or leak-down test will tell you if the rings are leaking, while a fluttering vacuum gauge needle will help you identify worn valve guides
March, 21, 2011 AT 1:52 AM
The most common cause of this code is for catalytic convertor failure, which the only repair is replacing it, keep in mind, these converters are not likely to fail without an external cause. Typical causes are: fuel pressure regulator leak, engine misfire, dirty fuel injectors, coolant consumption, etc. Also, be aware that some converters on the market will cause this code or codes due to a lack of oxygen storage capacity. A component that must be in these converters, Cerium, is required to store, then slowly release oxygen. NOTE: P0420 is a bank 1 converter code, P0430 is a bank 2 converter code. If the vehicle has only one converter, then P0430 does not apply.
March, 21, 2011 AT 1:53 AM
Sorry Raz, beat me to it again.
March, 21, 2011 AT 2:07 AM
Lol-this is how it works-you snooze you lose-lol-you are doing an outstanding job keep up the good work maybe you'll join me in the 2carpros hall of fame-just joking-Later m8-keep moving I love your style.
March, 21, 2011 AT 7:16 PM
I really appreciate the information provided in the response - very thorough and complete. As a follow up question, is there a sensor in the converter that feeds data to the computer so that, if the converter was totally removed (not just replaced), would you still get this code?
March, 21, 2011 AT 9:24 PM
No there is not a sensor in the convertor, but there is a o2 sensor before and after the convertor that sends signals to the ecm, to make a long story short, no you cant remove the convertor as the two sensors would mimic each other and it would set a code right away (P0420). Same code you already have because the Two O2 sensors are reading the same exact numbers so the computer knows the convertor is not doing its job.