[jmmullin]

Hello,

Wife's car had check engine light come on, and it was a P0420 code. Oxygen sensors were replaced, waited a couple weeks to see if the CEL would go out, and it did not. Today, the car has developed an occasional misfire in idle and sometimes at slow speed, but at highway speeds, the engine seems to run fine. After a short drive on the interstate just now the car appears to be back to running normally.

Symptoms while driving slow and idleing were occasional bucking (only while driving obviously) and flashing CEL for misfiring. She wasn't far from home so she went back and parked it. She's planning to head to a parts store to have the codes run again tomorrow, but no dealers or shops will be open until Monday.

Any ideas on how the converter may be affecting this misfire? Partially clogged maybe? I told her this may be the problem and to try to take it to the interstate for some higher rev's to see if it can clear out the exhaust and like I said, it seems to be running normally now...so a new catalytic converter is in the future most likely. Any insight is appreciated if others have had similar experiences, as I'm 1500 miles from the car at this time due to work. The car only has problems when I'm not around!

 

[jfoj]

Got to stop with all the nonsense.

P0420/P0430 is an INDUSTRY problem. Many, but not all of these codes are nuisance codes due to faulty fuel management system issues and not always a catalytic converter problem.

Changing O2 sensors is usually not the solution either. A lazy 02 sensor is less likely to trigger a P0420/P0430 code than a new, fresh sensor.

Start with the basic.

Engine operating temperature. I estimate that over 35% of the cars and trucks on the road have soft thermostats and are running too cold. Engine needs to operate at least 200F at idle.

As for your misfiring, the 2.0 is subject to coil issues and spark plug wire issues.

But you REALLY need your own OBDII scan tool that can read and display Live/Real Time data.

Read the links below in my signature.

Also read this - http://newbeetle.org/forums/1-8-liter-turbo/58960-p0420-code.html

Keep in mind you could also have fuel related problems as well due to all the cold weather than has recently hit certain areas of North America - http://newbeetle.org/forums/1-8-liter-turbo/74426-cold-weather-starting-performance-problems.html

 

[jmmullin]

Could you elaborate on how the thermostat could be related to a catalytic system efficiency below threshold code? The only way I could think to connect the two would be if the engine runs cool then the not as much fuel is actually combusted and a rich mixture runs through the exhaust. Is that what you are guessing?

 

[jfoj]

Read all the links posted in my prior reply.

Rich conditions and cool running engine can carbon up exhaust/converter/O2 sensors.

Replacing the catalytic converter is one of the very last steps I take with P0420/P0430 codes.

Fix the basic stuff first.

 

[jmmullin]

Read all the links posted in my prior reply.

Rich conditions and cool running engine can carbon up exhaust/converter/O2 sensors.

Replacing the catalytic converter is one of the very last steps I take with P0420/P0430 codes.

Fix the basic stuff first.

Bought one of the scan tools you recommended: Autel MaxiScan MS509 OBD-II/EOBD Scanner : Amazon.com : Automotive

Reads the engine temps around 180-184 while driving (it was in the 20's outside) and 190-194 while in idle in the garage after driving. Thermostat appears to be opening and closing normally (temp goes up, opens, temp goes down several degrees, closes, temp goes up, and so on). Do you think the stat is functioning fine, but opening too early? Doesn't appear to be anything wrong with the engine temp sensor.

I'll try to have her get a replacement thermostat. Will the 180 degree stat be good enough to get up to 200-205 range or should we use the 195 degree stat?

 

[PRM502STREET]

It looks like your thermostat is functioning properly. Address your misfire issue, it's usually pretty simple. And take care of that catalyst insufficiency code! Very simple also. You can do it for about $12 worth of parts, and about 10 minutes of Labor.
Look around here for a thread named gutted out cat, there is a tutorial in there on how to use these. You can also do an internet search on the part number,and see how other people have had results from the same product.

Sent from AutoGuide.com App

 

[jfoj]

Bought one of the scan tools you recommended: Autel MaxiScan MS509 OBD-II/EOBD Scanner : Amazon.com : Automotive

Reads the engine temps around 180-184 while driving (it was in the 20's outside) and 190-194 while in idle in the garage after driving. Thermostat appears to be opening and closing normally (temp goes up, opens, temp goes down several degrees, closes, temp goes up, and so on). Do you think the stat is functioning fine, but opening too early? Doesn't appear to be anything wrong with the engine temp sensor.

I'll try to have her get a replacement thermostat. Will the 180 degree stat be good enough to get up to 200-205 range or should we use the 195 degree stat?

Your thermostat is soft, it is not working properly, your engine temperature is too low.

The standard thermostat I believe is a 185 stat, this would be fine. What happens is the engine will not and should not run at the thermostat temperature, it should run/measure higher based upon where the coolant temperature sensor is located. Usually the engine temp will read/display about 20F higher than the actual temperature listed on the thermostat.

Now that you have a scan tool, check the Freeze Frame data and see if you can determine when the misfires are occurring.

The 2.0l has issue with the ignition coil and spark plugs, but you also have to rule out lean misfires due to vacuum leaks and other issues.

Read the first link below in my signature on engine temperature.

Do not jump on installing a spark plug anti fouler in the exhaust. You may or may not want to go down that road. The 2.0l also did have converter issues where they would self destruct and some were even replaced by VW beyond the normal warranty time frame under an extended warranty.

So sometimes the spark plug anti fouler can actually be a bad thing and cover up a semi catastrophic problem.

Get the engine running warm enough, the fuel mixture should balance out better and make sure you have no vacuum leaks or secondary ignition problems.

Until then, I would ignore the P0420 codes and just manage them for now, clear them as needed and if you are finding and correct the issues, you will likely see the P0420 code occur less and less frequently.