Question about 1996 Jeep Grand Cherokee

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Error code 420

The cat has been replaced.What esle could it be?

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Oxygen sensor

Posted on Oct 11, 2008

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What could be the reason that I keep getting a Cat Code CEL?


Po 420 cathalytic ineficient i say on you tube a guy you clean is cathalytic convertor with seafoam i try to find it for you

Apr 10, 2015 | 2005 Dodge Caravan

3 Answers

I replaced catalytic converter in my 2006 Pacifica and after two months check engine light came back on,code 420 bad cat.


you will get this code when the incompletely burned fuel in the cat has built up to a certain level and cat can no longer absorb more. The cause of incompletely burned fuel in the cat can be due to many reasons:

1. sparkplugs not firing correctly (wrong gap or fouled)(problem with ingntion components(wiring to spark plugs to high resistance)
2. fuel injectors are fouled.
3. bad fuel, incorrect fuel (regular vs premium-see user manual)

You will have to verify plugs are good, plug wires are good, injectors are clean, fuel is good.

once you get these things line out the light will eventually go out.

Jan 25, 2015 | 2006 Chrysler Pacifica

1 Answer

How do I pass vehicle inspection O2 Cat. Evap for a 2004 Chevrolet Cavelier


What was the code given..
02 will mostly sensors..
Cat code 420 will need new cat
And evap codes can b a couple different parts..need exact codes to tell what all is needed for fix

Sep 22, 2014 | 2004 Chevrolet Cavalier

1 Answer

Po 420 ?


code p0420 refers to cat converter system, bank 1 efficiency below threshold===causes --cat converter--wiring HO2S sensor 2

check that the cat converter is ok and replace the sensor. ( it is a HO2S sensor which will be different to a O2 sensor so get the right one )

Sep 12, 2014 | 1998 Chevrolet Astro

1 Answer

How do I fix Code 420 on a 1998 Chevy Astro?


Cat code ..02 sensors replacing may not fix that

Sep 12, 2014 | Cars & Trucks

1 Answer

I have a 2003 saturn ion 4 door, it has a ton of miles 194k. Last week the alternator went out do I replaced it without a problem, then the day after the check engine light came on I hook up the diagnostic...


p0420

no FSM> and not looking up P0420?
no engine stated, so ill get it wrong too..?????????????
420 is cat monitor failure. "efficiency"
the most hard of all.

ill make a list from hard and expensive .
1: bad sensor 2 rear. you failed to do both, that was WRONG.
2: bad cat. (i can weld on any cat for $99 bucks.) i do it last.. dead last.
3: engine running real bad. BUY a scan tool, now.

so the o2 is new that leaves #2 or #3.
i never shot gun cats. but shops do, its not their cash, huh?

i connect a real scan tool (not one that misses factory DTC codes)
then look at pendings for P042o , see funny sensor readings there, bingo.
i check every PID. for all sensors to be sure they READ right.
ECT AT 180F+ AND HOLDING? HOT.>?,
is the engine holding closed loop status at idle, no fix that NOW.
is LTFT (long term fuel trim ) near 0 or at - 40 or + 40% (fix that next)
if trim is good, the engine.
If the front 02 is new, the AFR will be correct and the the front 02 will swing fast and the trim will be near 0 , -4 is near best.
tad rich , natural.
once the engine is running Stoich at light flat cruise. (close loop) the
cat will heal its self (bake dry) and stop throwing 420. ( a hope deal)
if not the cat is bad.

ive cured some of the most hard 420s,.

on some ratty engines, a new cat can in fact hide it , until it cooks to death and next year 420 are back.
id never do that because gas is expensive. fix engine first.

Jun 24, 2014 | Cars & Trucks

1 Answer

What to do to fix a 420 code


420 is a catalytic converter afficiency code. It could cause by many problems: bed fuel, old spark plugs, sensor wiring connection. I would replace plugs and fill with premium fuel, turn off the code and drive to see if it comes back. If it does, stop by any muffler shop and have them run cleaner threw your system, it may give you 5 to 6 month driving but sooner or later you will need new cat for your car. Hope it helps.

Apr 30, 2014 | 2005 Chrysler Pacifica

1 Answer

Bank 1 p0420


Sometimes replacing the sensor fixes the problem, but more often the catalytic converter is at fault.
Code 420 means the converter is not performing up to standard. The engine computer is getting too much activity from the sensor after the cat than it should be. The number 2 sensor should be less active than sensor number one before the cat.
You would need to use a scanner to watch the data flow from the sensors and measure the temp of the cat to verify the problem.

Feb 04, 2014 | Pontiac Cars & Trucks

1 Answer

Buick errors 420, 401, 1406


P420 is EGR system malfunction P1406 is EGR pintle position problem be sure and check power and ground before condemning the valve and the P401 is catalyst code i would fix EGR code first clear monitors and run a drive cycle to see if the cat code returned although the egr and catalyst are separate systems an EGR that isn't functioning may cause the emissions levels to be too high for a marginal converter to diffuse resulting in the cat efficiency code

Dec 10, 2012 | Cars & Trucks

1 Answer

CAR SHUTS OFF TCS IS DISPLAYED, EGR VALVE RECENTLY CHANGED, 420 CODE IDENTIFIED. ALSO A GREEN KEY IS DISPLAYED MOMENTARILY.


The 420 code means you need the catalytic converter replaced. The TCS means Traction Control System. The green key is the theft system. Both lights MAY have nothing to do with the car shutting off Sometimes those lights will display when something elese makes the car stall. Perhaps a faulty crank sensor or the cat is so clogged its stalling out the car.

Mar 08, 2010 | 1999 Acura TL

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