Hey, I just recently bought an 01 Neon with the High Output 2L engine which has 64,000 miles on it. The first time I put gas in it, the engine light comes on with a P0420 code. I put in the 87 octane gas and I read later that the engine prefers 91 octane. Could that cause the code? It says it's the catalytic converter, but could that mess up the emissions and O2 sensors to cause that?

 

Using a lower octane may cause pinging, but it shouldn't do anything to the O2 sensors or cat. Try resetting the PCM and see if it comes back.

The neon O2 sensors are a bit quirky. Some last forever, others start having issues well under 100k miles. It's hard to tell when they're acting up or just reading normally though, and they aren't cheap... Do a google search and find out if the '01 cars fall under the newer EPA guidelines for emissions control equipment. I don't recall the number of years/mileage, but you may be able to have the dealer replace the cat for free (including labor) if it truly is faulty. I think for my car it was a 5 year/50,000 mile thing, and it was later put up to 7 years, 75,000 miles. I'm too lazy to do the research right now... I'm WELL past any of those marks...

Best of luck!

 

Thanks Radar... I did reset the PCM and it stays. I use a CarChip EX to read the codes. Wouldn't the O2 sensors have thier own code if they were bad? Is the Catalyastic converter code derived from the O2 sensors... I would think so since there is no sensor on the Catalystic Converter. Which sensor is the most likely culprit? I'm going to see if the CarChip can capture the actual voltage off the sensors. I think it can.

The reason I asked about the gas, was that the light cam,e on just minutes after filling up and I was driving for a while prior.

 

I got it fixed. It was the O2 sensor on the after side of the catalytic converter. The sensor was loose. I just got the car and haven't went through everything yet. After tightening the sensor, the light didn't reset, but the codes stopped recording and the O2 sensor voltages looked good. It seems my CarChip EX doesn't reset the Engine light. It does on my Ford pickup?? In anycase, unplugging the negative terminal for 30 minutes took care of it. All is well. Now... if the clutch can survice my 17 year old daughter learning to drive a stick!!

 

The PCM compares the readings between the two sensors and throws a CEL at a particular limit. A loose/leaking sensor, like you found, would do the trick. The downstream sensor does have some input into the fuel trim calculations, but the PCM probably didn't use them because they were wildly different than the primary (upstream) sensor. Glad it's fixed though!

Wouldn't worry about the clutch too much... I was teaching my son to drive in my car (and truck) before he went out to live with his this last summer. If you do start to notice it slipping, you can replace it with the PT Cruiser clutch which is a little beefier (and cheaper, for some reason). I think most folks are paying $200-250 for the unit at discount dealerships like www.dodgeparts.com, www.fsautomall.com, and Fenton Dodge (they don't have their own website, info/space provided at http://neons.org/forumdodge ).