2004 Lincoln LS • 6 cylinder FWD Automatic • 54,000 miles

Lately, the check engine light my 2005 Lincoln LS with 54,000 miles on it went on.

First thing that the computer at my mechanic's said it needed new coils and spark plugs.

Light went on again, showing 2 warnings, one being O2 sensor and the other the catalytic converter. He replaced the front O2 sensors.

One week later, check engine light went on again. This time, only the catalytic converter showed up on the analysis. Because I live in California, this repair would cost me upwards of $2000. When I asked the mechanic what would happen if I don't fix it, he said the only thing would be that the car would not pass the smog test. As it was just smogged in June and will not be required until June 2012, I am inclined not to fix it now. Is this a bad idea?
November 17, 2010.


Causes Of Converter Failures
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

Nov 17, 2010.
If the code you got was a PO420, then that is a Catalyst efficiency code and not an emergency but you will need it well before inspection because the computer takes time to reset all the monitors so it will pass inspection so don't wait till the last minute.

Nov 17, 2010.