Emission code P0420, Can someone please explain code to me?

335

Asked by Aug 22, 2014 at 08:03 PM about the 1999 Dodge Ram Van 3 Dr 1500 Cargo Van

Question type: Maintenance & Repair

My check engine light came on with a P0420 code, which means,catalyst system below threshold Bank 1. Can someone tell me what that means in terms of what the problem is?
Thanks, Tony

22 Answers

146,575

A catalytic convertor problem. But not necessarily anything wrong with cat. The o2 sensors, one upstream (before) and one downstream (after) should read different before and after the cat. If they reads the same it triggers this fault code. See: http://www.obd-codes.com/p0420

4 out of 4 people think this is helpful.
335

If it is a sensor problem, there would be a separate code for which one is bad, right? Could converter be pluging up some how? Is there a way to test sensors?

3 out of 3 people think this is helpful.
146,575

Yes, in fact the cat converter could be partially plugged restricting exhaust flow, but you would notice a great deal of power loss. And it depends on the scanner, A cheap one will not. A professional-grade will. Yes, sensors can be tested. I need a minute.

3 out of 3 people think this is helpful.
146,575

http://www.ehow.com/how_5193043_test-sensor.html ...http://www.youtube.com/watch?v=7uqmYkl7t0c.....http://www.youtube.com/watch?v=7uqmYkl7t0c.....http://www.youtube.com/watch?v=QM2jO0_Cah0 ....You will need a good multi-meter

3 out of 3 people think this is helpful.
146,575

The best way to ruin a cat is to put leaded gas in it

2 out of 2 people think this is helpful.
335

There is a bank 1 code & a bank 2 code. What would be the difference between the two?

3 out of 3 people think this is helpful.
59,175

Bank one is the side the #1 cylinder is on. Bank two is the side the #2 cylinder is on. HTH. -Jim

2 out of 2 people think this is helpful.
335

If the code is saying it is from bank 1, should I check everything real good from that side?

146,575

Is this the van?

2 out of 2 people think this is helpful.
146,575

You need to test or replace the 02 sensors on bank one. I don't know if they use heated sensors or not. A heated sensor makes the engine go in to closed loop sooner.(A whole 'nother story) Have you noticed power loss? ....click image to see it better The arrows are a bit confusing, they are pointing up to where the sensors are, not shown I will see if I can find an image of exactly where the upstream sensors are but I need to know, there are 3 available engines for 1999-- 3.9 , 5.2 and 5.9 Liter Even a better image than this drawing it's just an example ..a guide, not even your van

4 out of 4 people think this is helpful.
59,175

Now, on fordnut's picture the two oxygen sensors to the upper left are the upstream oxygen sensors (ahead of the catalytic converter). The one sensor to the lower right of the picture is the downstream oxygen sensor. The upstream sensors monitor and adjust the air/ fuel fuel mixture based on the exhaust gases coming from the engine. The downstream oxygen sensor monitors the catalytic converter. That's it's only job. HTH. -Jim

2 out of 2 people think this is helpful.
335

Hi everyone, thanks for everyones input! I have only 2 sensors, one before & one after cat. Yes that is the van we are talking about.I have a 5.2 engine. Sometimes lately the engine sputters or doesn't want to accellerate when I press on the gas pedal. I did change the cat 7 years ago, the ceramic insides collapsed plugging up the exhaust flow. Right now I don't feel a loss of power, just the smell of a rich gas mixture or unburned fuel.

1 out of 1 people think this is helpful.
335

Hi, I'm going to change both sensors & see what happens

1 out of 1 people think this is helpful.
59,175

If it throws the same code after changing the sensors you're going to need a catalytic converter. Since your van is a '99 model it probably does not have California emissions but check the emissions decal under the hood to be sure. If you see the words California or CARB Compliant you have California emissions. If not you have Federal emissions. It does make a difference with the converter but not the oxygen sensors. Just keep that in mind if you wind up having to replace the converter. HTH. -Jim

1 out of 1 people think this is helpful.
335

Hi , I had to take the cat off to get to sensors, once off I checked cat out & the ceramic inside is gone. It is a hollow shell of metal. I guess we know what the problem is now. What do you think would cause ceramic part to dissintergrate?

2 out of 2 people think this is helpful.
59,175

If you have high mileage and given the age of your van, possibly just normal wear. Especially if you're not having any engine problems (misfiring, burning oil, etc.). Things wear out. HTH. -Jim

2 out of 2 people think this is helpful.
Best Answer
335

Hi, the engine only has 88500 miles on it, changed cat 6 years ago, that one broke up & plugged the exhaust opening. The new cat had only 21000 on it.This one is still under warranty.

1 out of 1 people think this is helpful.
59,175

Wow, with only 21,000 miles on it, that converter shouldn't have failed. Unless there's been problems with the engine. One thing that will cause a converter to fail prematurely is if it's not installed correctly. The new converter must be warmed up properly when the engine is first started after installation. This just involves running the engine at a fast idle for around 5 minutes before the vehicle is driven for the first time with the new converter in place. Eastern Catalytic Converter has a video explaining this procedure in more detail on their website. Be sure the shop does this for you before you drive the van for the first time with the new converter in place. HTH. -Jim

1 out of 1 people think this is helpful.
335

Hi Jim, I have been doing all the work on van. I did not know to do the procedure you just explained, but will make sure this time. Thanks, Tony

1 out of 1 people think this is helpful.
59,175

You're welcome, Tony. Many people don't know about the warm up procedure. Check out Eastern Converter's website. It's very informative. There's other videos on there too explaining how converters work, things that can make them fail, etc. Glad to help. -Jim

1 out of 1 people think this is helpful.
335

I got cat replaced under warranty, new sensors, & this is the recommended break in procedure for cat converter. This procedure come from Eastern Catalytic Converter website. Start engine, do not put foot on gas pedal! Idle engine for 5 minutes to slowly warm up converter. Then increase RPM to 2500 & hold there for 2 to 3 minutes.Turn off. Allow engine to fully cool down. Hope this helps someone, Tony

59,175

Awesome, Tony! That's what I was talking about. Glad you got it fixed and shared the procedure. I'm sure it will help others. Thank you very much! -Jim

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