My exhaust system warning light is on. What could this mean? I have just had the oil changed and use regular gas. I always tightened the gas cap fully after several "clicks". thanks

P0420 & P0430 You need new catalytic converter
The P0430 check engine light code, like P0420, means the catalyst system efficiency is below the required threshold. Simply put, this means your car is adding more pollution into the air than it's supposed to.

yes
ignoring lights leads to complacency and a large repair account that could have been avoided if attention was paid in the first place
exhaust light codes are in the p1400 list and refer to the EGR valve system ( exhaust gas recirculation)
I would find an accredited service center that has experience on your make of car and have the fault codes read and the problem properly diagnosed
what you dealer stated about the gas cap is an EVAP issue and if he didn't read the codes first , he has done you a disservice and not attended to your concerns properly

Common in automobile emission systems since the early 1970s, the EGR (Exhaust Gas Recirculation) valve controls an engine's emission of smog-causing nitrous oxides, or NOx. Its job is to route a portion of the exhaust gases back into the intake manifold. That lowers combustion temperature to below 2,500 degrees Fahrenheit - the temperature at which NOx gases form.

EGR flow is controlled by the engine's computer, which opens or closes the valve as needed. The EGR system is, for the most part, in the "out of sight, out of mind" category, and typical doesn't require regular maintenance. But if it gets clogged with carbon deposits, you'll see your "check engine" light come on, and a code (perhapsP0401or P0402 or P0403) will show that there is insufficient flow. That typically results from a vehicle being driven persistently on short trips that don't allow the engine to fully warm up. Flow problems also can be caused by carbon buildup due to failure to change the oil frequently enough.

A clogged EGR valve not only results in higher emissions, it can affect fuel economy and cause rough idling - even serious engine damage. Valves can usually be cleaned, but replacement is often recommended.

Advice? Make sure to put on some highway or freeway miles, and always change the oil according to the maintenance schedule in your owner's manual.

Hello,
This is a common issues with this truck. You have probably tightened the gas cap a bunch of times and are like what the heck. The gas cap DIC warning is part of the evaporative system to reclaim gas vapors. The onboard computer on the truck monitors the gas tank vapor pressure, which checks for vapor leaks in the fuel system. This warning involves a pressure mismatch, which the onboard computer relates to a fuel vapor leak. It assumes fuel vapors are escaping via your gas cap thus circumventing the purpose of the evaporative system. A common fix is to dip your finger in a bit of motor oil and put it onto the gas cap gasket to seal it (like you do an oil filter.) This should solve your problem. If the gasket is ripped or torn then buy a new gasket or a new gas cap. The reason for the oil is to lubricated the gasket again as they get very dry over time, given their location.
Regards, Tony

This probably means:

• P1456: Evaporative Emission Control System Leak Detected (Fuel Tank System)
• Usually this is because your gas cap was not fully tightened. Be sure to turn it until you hear a click.
• After you tighten the cap, it might take a couple days of driving before the light goes-out.
• Be careful to tighten your gas cap regularly, because otherwise it puts a heavy strain on your emission system.

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Yes it is time for an oil filter and oil change specially if there is a lapse of over 10 months or a mileage of more than 5000 miles clocked since the last oil change.

Yes, first try securing it tighter. This means until you hear it making noise. Go to advance or autozone and have them reset the code. If it still turns the SES light on, replace the cap. My 2001 DTS did the same thing at 144K. You may be on the same track I am on. So far I replaced that, the EGR solenoid (get the Delphi brand) and now it looks like I have to replace my EGR vent. During this I also had to replace my fuel pump. Fortunately on this model it's easy to get to through the trunk. I ended up having to splice in a new connector. They don't come with the old one any more. Good luck.

Almost every newer vehicle has the fuel filter in the top of the fuel tank. Good luck

it means that if u have a catalytic converter then ur catalytic converter which reduce the emissions is not working in proper manner which it means that it is broken

Your vehicle’s computer system has self-testing capability. When the computer senses that there is a problem with some of the components it stores the correspondent trouble code(s) in its memory and lights up the Check Engine or Service Engine Soon lights to tell you that there is a problem and you should have the car diagnosed and repaired. Not fluid related, but could be a small problem that's easy to fix now. Even a loose gas cap can turn the light on. Have a code scan, that's the starting point.