P0420 CODE

90

Asked by Dec 31, 2015 at 08:21 AM about the 2002 Mercury Grand Marquis GS

Question type: Maintenance & Repair

Check engine light code reads P0420, what does
this mean?

27 Answers

52,225

Possible causes - Three way catalyst converter Bank 1 - Exhaust tube - Intake air leaks - Fuel injectors may be faulty - Fuel injector leaks - Spark plugs may be faulty - Improper ignition timing - Engine Control Module (ECM) What does this mean? What does this mean? Tech notes As the code description implies the P0420 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0420 code is combined with other codes, try fixing the other codes first. What does this mean? What does this mean? When is the code detected? - Three way catalytic converter Bank 1 does not operate properly. - Three way catalyst converter Bank 1 does not have enough oxygen storage capacity. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light)

4 out of 4 people think this is helpful.
90

Basically I need to replace the catalytic converter on bank 1, is that what you are saying and if so how much does that cost I just changed out the intake manifold

1 out of 1 people think this is helpful.
52,225

What kind of troubles are you having? There are options depending on where you live, for emissions reasons. Looking in one of my on-line stores, to replace that section of pipe is like $350 bucks.

2 out of 2 people think this is helpful.
90

The car is running smooth the check engine light just jumped on out of nowhere yesterday but I seem to have no symptoms or signs of anything going wrong

3 out of 3 people think this is helpful.
90

When the intake manifold was leaking antifreeze coolant, I'm assuming some may have went into the exhaust and catalytic converter

2 out of 2 people think this is helpful.
52,225

If you were blowing out a lot of white smoke out the exhaust or a lot of condensation coming out the tail pipe , but normally this is not the cause for the break-down of the catalytic converter. Normally over time a cat will plug-up from carbon and what-ever crap comes out from the engine. (for lack of words) There is a slight chance the 02 sensors may be at fault. Are you starting to have acceleration problems? Engine holding back? These are indications of the cat. getting plugged up. I will be back in 2 hrs. If any more questions please post.

90

It was doing all of the above until I changed my coil packs and spark plugs

90

Car runs fine although I know I have an exhaust leak somewhere under the car because I hear a noise from the exhaust leak but that has been going on for several months now

40,755

An exhaust leak depending on where it is and how serious may be the problem.

1 out of 1 people think this is helpful.
52,225

Yep like Bob says, possible that the 02 sensors are picking up an abnormal condition in the exhaust because of the exhaust leak. I wouldn't jump right in to replacing that $400 dollar pipe just yet. I think I'd just fix the exhaust leak with what-ever pipes necessary. Then get the code cleared. One way you could check the cats is at night take it for a drive, get her warmed up, go somewhere dark and look at the cats. If they are plugged, you will see an orange glow to them.

1 out of 1 people think this is helpful.
6,255

420 lack of switching, freeflow like the hippies.

2 out of 2 people think this is helpful.
52,225

Ok there Guy, your talking about one from the past...he,he,he,

2 out of 2 people think this is helpful.
90

I'm going to check my catalytic converters tonight after driving for a while for an orange glow

1 out of 1 people think this is helpful.
52,225

Sounds good, just don't want you to be throwing monies away...

1 out of 1 people think this is helpful.
90

I just replaced all coil packs, spark plugs, my EGR valve recirculation tubing, and my intake manifold as well as the thermostat

90

The light came on one day after getting it out of shop but the car has been running fine before and after the light has been on

52,225

Starting to not think it is the cats. Still check it out this evening. Just leaning more toward that hole in the exhaust, effecting the 02 sensors readings.

1 out of 1 people think this is helpful.
90

I changed one cat about three and a half years ago

52,225

Like I say, just check it out this evening, then get the exhaust repaired & have the code reset and go from there, Let me know what you see tonight. Leave the car running when you look.

1 out of 1 people think this is helpful.
90

How long should i drive before checking under car

90

Also should I have the car jacked up or anything

1 out of 1 people think this is helpful.
52,225

Drive the car down the highway for about 10-15 min. after it is warmed up in town, and as long as you can see the cats looking under the car thats good. I myself try to make it easier to see under the a car by looking for a dip to park over or somewhere to park to give more room to see. Best to look right away when you park.

2 out of 2 people think this is helpful.
6,255

Thanks Rowefast, my previous comment about free flowing is that a p0420 usually indicates that the cat cant store oxygen any longer. When this happens they will allow the exhaust to pass right on through without doing its job. O2 11 will switch normally from .1v to .8v and o2 12 will be switching the same when O2 12 should be staying at about .7v steady. If this is the case then it's like having no cat on the vehicle at all. Eventually carbon will build up on the catalyst and cause a restriction. You don't have to jack the car up to look at it just be able to see it under the passenger side of the vehicle.

90

I'll let you know as soon as i do it

90

You seem to know alot about cars, can you tell me anything about Pontiac Firebirds and if that's a great car

40,755

Pontiac = out of business. Probably a reason for that.

1 out of 1 people think this is helpful.
90

Lol, i guess you're right

1 out of 1 people think this is helpful.

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