Question about 2005 Ford Fusion

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Engine fault indicator comes on but CAT has been replaced

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There is a light on my dash board which is on which mean service engine soon and i service the engine the light did not go off, what can i do pls.

Posted on Mar 04, 2013


If a Converter has to be replaced, in less than 12 years,you got issues,that should have been diagnosed and repaired first.

Why didn't you give us the codes, and some drivability issues?

Posted on Sep 30, 2010

  • rwelland Sep 30, 2010

    Thank you for your info.
    I was not advised the Fault Codes by the garage so could not quote them. There are no known issues regarding driveabilityso far but we have only done 750 -800mls since buying the car 2nd July this year.
    It doe's concern me that you state that a CAT Converter should not need replacement in less than 12 years, this seems a long time and could equate to some 150,000 mls or more.



  • Anonymous Oct 01, 2010

    I had an 1986 Cadillac for 17 and a half years
    I just parted with a 1992 Dodge Dakota,end of june,had that 18 years,four months
    All original converters and always passed inspection,only put in one O2 Sensor at 100,000 on Caddy, just for maintainance,not failure.
    My 26 year old 1984 S10, has a converter I put on in 1993 or 4, 17 years approx.

    Converters fail from being overheated--Ignition Misfire,or Rich Fuel Mixture,most common,then you got coolant and other bad things we won't discuss

    All Fords with COP Ignition Coils,going back to approx 1998 have coil failures, once or twice a year.
    My wife has a Lincoln LS, I got a lot of experience there. 47 Years of doing my own diagnostics.



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Driving in town no problem but when driving on freeway check engine light come on and car is hurling like it have fuel starvation. 3lt xenon decor 2010 118600km on clock

indicates a venting problem in the EVAP system or a blocking cat converter
the fault codes reading will indicate the problem area

Jul 13, 2017 | Cars & Trucks


Car runs rough or cuts out when engine warms up

If your car starts perfect from a cold start then starts playing up when it reaches normal running temp, or if it even cuts out and then wont start again until the engine has cooled down then your going to need to get the following checked.

the most likely cause of your problem is going to be a bad oxygen sensor or lambda sensor for its proper name, now the reason it points towards this being the fault is that this part does not start working until the engine or exhaust is near normal running temp.
so you will find that your vehicle will start and run perfect when cold how ever as soon as the engine gets warm this part will start working and cause the car to cut out due to it sending the wrong info to the car fuel management system.

now you also need to bar in mind that this also depends on where your oxygen sensor is in your exhaust now if the sensor comes before the catalytic converter then the chances are your problem is going to be with this sensor, how ever if your sensor comes after the cat then it could also be the cat that is at fault.
if your cat comes before the sensor then it would be a good idea to have a diagnostic check done as you could spend money replacing the sensor and find out the fault it with the cat so bare this in mind when finding out the fualt

on May 26, 2010 | Ford Focus Cars & Trucks

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Took my 2003 Toyota 4runner in because engine light was coming on intermittently. That has happened before. Also complained of sulpher smell twice. the first time car was 6moths old...they said changed...

No it is not under emissions warranty the year is what is the factor, it is 7 years or 70,000 mile whichever comes first. You need the check engine fault code read and that fixed first, it is most likely the cause of the smell from the catalytic converter which is caused by a overly rich fuel air mixture. The fact you smelled the sulfur indicates the Cat is working. I was a certified repair and inspection technician for the Calif smog control program for 35 years.

Apr 25, 2017 | 2003 Toyota 4Runner Limited V8

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I just got the code po 420 how do i fix it

Most likely a worn out exhaust converter

PO 420 -- Catalyst System Efficiency Below Threshold (Bank 1)
that is the right or pass side

Rear or Monitor Sensors could be bad ,if converter is less
than ten years old

Aug 06, 2011 | 1996 Ford Explorer

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O2 sensors keep failing and a evap leak code i put new gas cap did not cgehan

Are you sure it's 02 sensors? Just because code says 02 sensors doesn't necessarily mean they're bad. Bad 02 sensor code can also indicate bad cat. converter. If 02 sensors read exact same reading before and after converter they will trigger OBC to "sensor fault" - they should be reading 2 different readings. (Pre CAT/POST cat) I'd suggest replacing cat converter before replacing sensors.

Mar 14, 2011 | 1999 Toyota Camry Solara

1 Answer

Cat system fault is on

replace the rear o2 sensors, or beat on the cat.. if it rattles inside there, it is the bad part. If the cat is bad, then check the engine out for the general state of tune. This is because if the engine is not running perfect, then the cat will take all the abuse.

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Code p0420


Normally, the P-0420 indicates a sensor issue; a cat replacement would be needed if you had the P-0420 coupled WITH a
P-0430 code.

What I would do, if I were you, would take the car to a shop that can perform an "induction cleaning", and have that service done. Then, replace the spark plugs, if the car is around 90,000 miles. You may alsop need a front air-fuel sensor (the one on the manifold) replacement.

I would not change the cat until I did the above services. It does not sound like a bad cat just yet.

Dec 30, 2009 | 2004 Toyota Corolla

2 Answers

Check engine light but no fault codes

Take the Accent to AutoZone. They will scan the code (free) and give you a print-out with a "general" explanation (free). They can also reset it properly.

Let us know the codes and a summary of the print-out. We will advise you.

Answers to your questions:
The sensors at the cat are O2 (Oxygen) sensors.
Problem could be the cat or could be a faulty sensor. My money is on the O2 sensor.

Could be lots of things, like sticky fuel injector...
Don't change the catalytic convertor just yet.
My opinion is that the "shop" doesn't really know and is hoping that replacing the cat will fix it all (my opinion).

If you eventually change out the cat, go to a local muffler shop, not a national chain. They will do the same job for a lot less and not try to sell you other stuff.

Oct 01, 2009 | 1996 Hyundai Accent

1 Answer

Indicator Lamp Warning

could be but it comes up for a reason
I suspect a cat converter malfunction and the explanation to keep the rpms lower indicates that it is not functioning properly or has failed and could be blocking the exhaust system
It could be a simple O2 sensor ( one after te cat converter) that has malfunctioned
don't wiat for the next service but have it checked out by an accredited service center and have the fault codes read

May 23, 2017 | 2002 Mini Cooper

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Catalytic convertor replacement on Mercedes Benz 430 ML

You could probably do this, but you're going to be running with a permanent check-engine light. The twin O2 sensors on each exhaust pipe are for emissions reasons. Your primary (pre-cat) O2 sensors help the engine determine how much fuel to inject, based on reading the level of unburned oxygen in the exhaust stream. Your secondary O2 sensors (post-cat) are there to provide a similar reading. The car's computer then compares these two values to determine the efficiency of the catalytic converters. If the comparison strays outside an accepted range, the computer trips a fault light.

If you have emissions testing or regulations to that effect where you live, you will not pass inspection. In addition, if you have smog laws that mandate cats and other smog equipment, you could be risking a huge fine if you're found to have removed them. I'd check with an auto parts store about getting some generic universal cats (make your choice based on the length of the cat assembly and the diameter of the inlet and outlet pipes). These are generally far less expensive and work just fine.

On a side note, are you positive that the cats are bad? If you're tripping a fault code for a failed cat, it could be that one or the other of the O2 sensors are bad and causing an indicated cat malfunction. I'd have at least a couple other places look at the car and see whether it's the cats or the secondary O2 sensors before shelling out the money for cat replacement.

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