2003 LS P0420 & P0430 at the same time

07-07-2011, 06:17 PM
Greetings, I have a 2003 Lincoln LS and just recently I have error code P0420 and P0430 come on at the same time. I know its for the left and right Cat converters that are below efficiencies but that is hard to believe that they both failed at the same time. It has to be something in common that caused both codes to come on at the same time. What is similar that would cause that? I did change the Mass air flow sensor at that time. could that cause it? I did buy it new from the auto parts store. All coils and plugs have been recently changed and there is no miss fire.

07-07-2011, 08:24 PM
If sounds like both cats are blown, see http://www.automotiveforums.com/vbulletin/showthread.php?t=915437

I can set you up with some HO2 simulators, that will suppress the P0420's + P0430's until you get new cats.

07-07-2011, 09:24 PM
Sounds great. Will I need 2 or 4? I have emissions testing coming up soon. Thank you for your help. Its just weird that they both decided to fail at the exact same time.

07-07-2011, 10:47 PM
Before condemning the (expensive) catalytic converters or installing HO2S simulators, check a few of the other possible causes for the codes. Agreed, it's unlikely that both converters would fail at the same time. Possible causes:

Use of leaded fuel
Damaged HO2S
Malfunctioning engine coolant temperature sensor
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
Leaking fuel injector

If you have a scan tool that will allow you to monitor the HO2S real time (datastream) that could tell you a lot as far as where to look.


07-09-2011, 12:27 PM
The down stream H02 sensors (2) are sending a feedback signal telling the ECU, that your cats are not working. The upstream (2)H02 sensors are used for a feedback signal for the ECU to formulate the Air/fuel mix 14.7:1

You should only need two down steam simulators, one for each bank, but you might need to two H02 sensors upstream, because something made your cats go bad.

How's your fuel economy?
Do you have a Check engine light on?
How many miles are on your car?
When was the last tuneup, and what did they replace?

A bad suspenshion could also damage the brick inside your cat!

I usually use H02 simulators until all the problems are resolve, else your new cats will get contaminated.

Two H02 simulators are $35, you can get OE Cats @ http://www.catalyticconverterwarehouse.com

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