P0420 in 1996 Ford Contour v6 SE

Not much use changing the sensors - but be SURE youn have no air leaks in the exhaust.

I have also found that sometimes a REAL GOOD "polish tuneup" solves the problem. Take it out and DRIVE THE SNOT OUT OF IT if it has been generally babied. However, if it has not had the water pump replaced, be carefull not to take it above about 5500 RPM - the plastic pump rotors generally let go somewhere around 6000.

The cat can be (sickened" with carbon, and a good hard drive CAN on occaision burn it clean and make it work again. Those cats are EXPENSIVE!!!!

I think I'd try cleaning the MAF sensor first. That took care of the P0420 I was getting on my 97 CV.

I guess you missed this part;

"This catalytic converter is for use on federal or California emissions equipped vehicles manufactured prior to 1995"

Try this link; pick the one that matches your car:

ANY catalytic converter for that car is extremely expensive. I've seen quite a few 2.5 Contours an Mystiques SCRAPPED because they needed converters - with just over 100,000km on them and almost MINT condition. Add bad brakes to the mix and they are hardly worth fixing

- as nice a car as they are (I love ours - as long as I don't need to fix it!!!)

Even the Merits are $505 and $484 and it's a crapshoot if they are any better than the one you are taking off. The Walkers are $748 and $894. Then there's still the third one (roughly $200) and the sensors (recommended to change with the converter. Sometimes you have no choice if they sieze in)

Before I replaced the convertor, I'd check the O2 sensors. The sensor after the convertor is used to determine of the convertor is performing properly. If it does not respond properly the PCM will set the P0420 Code. You odn't say how many miles are on your vehicle, but if it is over 100,000 miles, the O2 sensors may be the problem - at least they are a lot cheaper than the coverter ($40).

Ed

Not likely. The second sensor only causes the code if it DOES clock. If the front sensor clocks and the back sensor does not - no code. If the rear sensor follows the front one, you get a code. Never saw a rear sensor failure give a PO420.

You are right. However before I spent big bucks on a new converter I'd grasp at straws (at least cheap straws). I was actually thinking of replacing the front sensor instead of the rear. If the front sensor is lazy, can't it cause the code?

Here is what Ford says about the code:

DTC P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

Description - Indicates Bank 1 catalyst is below the acceptable threshold

Possible Causes - Use of leaded fuel - Damaged HO2S (Heated Oxygen Sensors) - Malfunctioning ECT - High fuel pressure - Damaged exhaust manifold - Damaged catalytic converter - Oil contamination - Cylinder misfiring - Downstream HO2S wires improperly connected - Damaged exhaust system pipe - Damaged muffler/tailpipe assembly - Retarded spark timing

Diagnostic Aides - Compare HO2S upstream & downstream switch rate. Under normal closed loop fuel conditions, high efficiency catalysts have oxygen storage which makes the switching frequency of the downstream HO2S quite slow compared to the upstream HO2S. As catalyst efficiency deteriorates, its ability to store oxygen declines and the downstream HO2S signal begins to switch more rapidly approaching the switching rate of the upstream HO2S. Once beyond an acceptable limit the DTC is set

You NEED to know the switching speed of both the front and the rear sensor to make a reasonable decision. The major causes are bad cat or exhaust leaks. Would help to know the HC, O2 , CO2 and NOX readings.

Does the car use any oil??

Firstly the car has 70K

I went to the autozone store today and we had a look under the car and on their computer system. The agent said there is only ONE catalytic converter ($150) With 3 bolts on each side I can do it myself

Does the contour have just one Converter ?

This is the part

I am going to try change the O2 sensor before the catalytic converter.

Do you know how many O2 Sensors I need to replace ? The autozone guys said I may have to change 2

Any idea ?

Thanks

What I mean assuming my 1996 contour SE v6 has only one Catalytic converter If I want to change the Oxygen sensor before the catalytic converter Do I need to change one or two sensors ?

What I mean assuming my 1996 contour SE v6 has only one Catalytic converter If I want to change the Oxygen sensor before the catalytic converter The autozone guys said there is a possibility there are two sensors before the converter Bank1 Sensor 1 and Bank 1 Sensor 2

Do I really have two sensors Do I need to change one or two sensors ?

Min VIN mumber ends in 7L6TK

Your assumtion is wrong. It has THREE converters.

Bank 1 and bank 2 each have 2 sensors. Then there is the third cat.

sensor 1 is the front one before the CAT, sensor 2 is after the CAT. bank # is the pass or drivers side. If it has two fronts, change them both. your discription shows only 1 front,(bank 1)

I would assume your car has some miles on it, so it sure wouldn't hurt to change the front sensor first (controlls fuel mixture) The rear sensor monitors the CAT but don't assume it must be that sensor that is the problem because'it monitors the CAT' !! Very unlikely.

As for a new cat, have you checked a local muffler shop? (and I don't mean midas or mineakee, if you can help it, usually high prices)

OK so I replaced the sensor but the light is back so I am going to have to change the cat I have zeroed in on this part