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Kansas City, MO
There are a variety of things that can cause the symptoms you describe. One common problem that can be intermittent and temperature sensitive is a leaking intake gasket. You need professional diagnosis to pinpoint the cause of the problems.
P0420 indicates the catalytic converter is performing below a predetermined threshold. The performance is measured by the rear oxygen sensor. If the exhaust manifold is allowing air to enter the exhaust system, that excess air can mess with the measurements made by the oxygen sensor. So to answer your question directly, yes, it is possible than a manifold leak could cause a false code P0420. However, it is not likely. There is also an oxygen sensor in front of the converter. If there was excess air in the exhaust, I would expect the front 02 sensor to see the extra oxygen and set a code for exhaust too lean. If that is not happening, then excess oxygen is probably not present and therefore, not responsible for your code P0420.
There are several possible causes of the symptom you describe. The most likely is that the blower controller, aka blower resister has failed. Late model Chrysler products are known for a pattern failure of the blower controller melting due to high current flow. If this happens, replace the controller and the blower motor. The blower motor is drawing too much current which melts the controller.
If the compressor is not functioning the air conditioner will blow warm. If the system is low on refrigerant, the compressor won't turn on. Either way, no cold air. Only a detailed inspection by a qualified technician will tell for sure. Of course, if the compressor is not coming on because the system is low on refrigerant, the question is "where did the refrigerant go?" If you have a system leak, that will have to be fixed first.
You need a wiring diagram to trace the circuit. I suspect the fuse is powered from the headlamp switch. If so, check power at the switch. The headlamp switch could be the problem.
The noise might be caused by a loose chain inside the transfer case. Or you could have a faulty U-Joint on the front propeller shaft. It is unlikely that the U-Joints on the front drive axles are causing the problem because you don't hear it when turning.
What problem are you trying to solve. Is it simply a leak or in the engine overheating?
The rapid flashing is being caused by the inoperative bulb. The only possible causes are a faulty bulb, faulty power supply, faulty ground or a faulty connection inside the socket. With a test light check for power the turn signal socket, then hook the test light to the positive side of the battery and make sure it lights up when you touch it to ground. If those are good, and I suspect they will be, then replace the light bulb socket.
I like to see no more than 1 quart consumed between oil changes. Since you should have done 2 oil changes in 6000 miles, your consumption is on the high end of normal. If you are using extended oil change intervals, which is only possible with fully synthetic oil, then max oil consumption should be no more than 1 quart every 3000 miles. Oil can only be leaked or burned, there is no other place for it to go. Check your positive crankcase ventilation system for proper operation and of course, check carefully for oil leaks. Look especially for those leaks that are under pressure, in other words, those leaks that only leak aggressively when the engine is running (such as an oil pressure sender) If leaks are not your problem, then you must be burning it. With compression of 185, I don't suspect rings. You might look at valve guide seals. Look for a blue puff of smoke on start up that immediately goes away when the engine is running.
Check the transmission range selector. The signal from the ignition goes through the range selector and won't allow the vehicle to crank over unless the selector is in park or neutral. The selector may be faulty or miss-adjusted. Try moving the gear shift while trying to crank the engine.