CEL 2003 hyundai elantra

Help!! one yr ago my CEL was on and I had my catalytic converter changed. car passed emissions and my CEL came back on about a month later, my mechanic said nothing to worry about. i now have to bring my car for emissions again and when i brought the car to the mechanic he said my map sensor needed to be changed. 200.00 dollars later the CEL came back on after about 120 miles. mechanic cleared the light, i brought it to emissions but it was too soon to be tested, but they said “your car is fine, no codes are coming up, you just need to drive it more”. CEL came on at only 50 miles this time and now took it to pep boys to get another opinion on the codes. po456 and po420 came up. any suggestions? thank you so much.

What did they reccomend? P0456 is for a small evap leak P0420 is catalyst system below efficency. Both codes need to be diagnosed properly.


Oh, if there was only a way to diagnose a small EVAP leak effectively… (:-/
Seriously, I agree with Steve. Have the causes diagnosed and post back.


Why so pessimistic?

Evap leak codes aren’t the worst thing in the world. An evap/smoke machine, common sense, trouble tree, patience, and the fault code setting criteria are a good starting point

The evap machine is nifty, actually. Not only does it put smoke into the system. it also shows you the size of the leak, and the solution has a dye in it, so you could see where the smoke came out, using your black light. The dye comes in handy for those really small leaks that you can’t easily see

As for the P0420, there are plenty of possibilities, such as . . .

The cat is (possibly again)partially plugged, because the root cause wasn’t addressed the first time
The front oxygen sensor isn’t switching fast enough, because it’s old
A cheap aftermarket cat was installed, which doesn’t have enough of the required precious metals
Exhaust leaks
The PCM needs a software update, because the fault code setting parameters are too sensitive

That said, Pep boys is no place to have the car properly diagnosed and repaired.

That said, Pep boys is no place to have the car properly diagnosed and repaired.

IMO PepBoys is not the place to even have replace a bicycle chain. But that’s just my 2 cents worth.

This kind of vehicle situation is why I still hate the CEL system or as I call it the “Profit Generator for Repair Shops” light. The sale and installation of catalytic converters and 02 sensors is probably twice what it should be in this country because of that $@*&%^# system.

The CEL is not a profit generator, its just there to inform car owners when something has gone wrong. The cost for shops to do diagnostic work is higher than most pepole realize. You often need factory level scanners which can require monthly subscriptions, access to bulletins and wiring diagrams, special equipment like smoke machines, and if you get into hybrid drivetrains a megaohm meter will set you back about $1000. To make the situation worse you have parts chains offering “free diagnosis”, with a list if parts that may solve a problem.

@SteveC76 … in a perfect world this would be true but we live in a far from perfect world and the light is used as a profit generator. I see and hear about it all the time. The CEL system was designed to help diagnose faults but it is used quite frequently to take advantage of people who know nothing of vehicles in the mechanical sense. I stand by my statement. I hope you are not naive enough to think that all the catalytic converters and 02 sensors sold and installed in this country were actually needed.

I agree with your you on that. I have seen way too many cars with every part but the right part replaced. I don’t blame it on the CEL, its more the guy who replaces a whole system for a single part.

Computers for cars is nonsense. We don’t need a computer to gradually dim the dome light in a Kia, nor do we need it to run an engine. Carburetors ran engines just fine, so did points and condensor. A simple machine is generally a reliable one.Sure I’d change points to peizoelectrics, still a simple design.Carburetors to Heat Exchangers, still simple. This technology wasn’t meant for this field but is being tested in every way shape and form.I hope it leads to something good.

Dusenberg, were you around in the days of carburetors and points & condensers? Modern electronic fuel injection systems are far, far more maintenance and problem free than our old cars ever dreamed of being. I fondly remember doing a tuneup every 10,000 miles, tweaking the dwell, gas line freeze up, vapor lock, sticky carburetor linkage, weak bimetallic choke springs, and countless other challenges inherent to carbureted systems and their pull-type low pressure fuel delivery systems. And things like carbon buildup inherent in dirty running engines… and there is truly no way to make a carbureted engine burn the fuel as totally and effectively as an EFI system; the hydrocarbon droplets inherent in a low pressure differential vaporization system are simply too big.

Dispensing fuel through an orifice at the venturi via only the vacuum developed cannot produce as small a droplet as dispensing it through an orifice with 40psi+ pushing it through. To illustrate, try squeezing a Windex spray bottle very slowly, producing a small pressure, and then fast, producing a large pressure. The slow pull will dribble out, the fast pull with produce a vapor. Since fuel droplets have an extremely small timeframe to burn through, and they can only burn from the outside HC layer inward, the small droplets of fuel injection burn much more thoroughly and the engine is able to use the contained energy much more effectively.

Fuel injection is not new, but it was the advent of electronics that enabled it to be used to its full advantage. The ability to use sensors and controls with virtually instantaneous detection and response truly is a blessing. Just as printed circuit boards were a Godsend to solid state devices, computers were a Godsend to fuel injection.

The real driver behind EFI is the Clean Air Act and its resultant emissions and CAFE standards, but it truly has resulted in substantially better operating engines by all metrics, cleanliness, power extracted from the fuel, reliability, and longevity of the engine.

@Dusenburg, please check the date on your computer. It seems to be dated 7 weeks ago.