Question about 2003 Hyundai Santa Fe

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P0420 engine code

Can a leak on the manifold cause this

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P0420 is a catalytic converter inefficiency code. The most likely problem is the catalytic converter is no longer able to function. The cat is monitored by the downstream O2 sensor. Unless there was a leak near that sensor than its unlikely (but not impossible) that an exhaust manifold leak is causing the problem.

What is possible is that the leaking exhaust manifold is skewing the readings for the upstream O2 sensors which could effect the life of the cat if the vehicle is running slightly richer than it should be.

Posted on Feb 24, 2012

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My volkswagen beetle is throwing a code of p0420 catalyst converter. i had two different mechanic tell me two different things. one says i have to replace ev erything from the manifold back and the other...


P0420 Volkswagen - Catalyst System Efficiency Below Threshold Bank 1 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)

Don't guess, check out the possible causes above.

Jun 05, 2014 | 2001 Volkswagen Jetta TDI

1 Answer

Code p0420


Just did the P0430,so here's the P0420 trouble code.Trouble Code: P0420

Catalyst System Bank 1 Low Efficiency

Possible Causes:


Air leaks at the exhaust manifold or in the exhaust pipesBase engine problems (i.e., high engine oil or coolant usage).Catalytic converter is damaged, contaminated or has failed.Continuous engine misfire conditions, or weak or low coil output.Front HO2S or rear HO2S is contaminated with fuel or moisture.Rear HO2S is loose in the mounting hole (check it for a leak).Front HO2S older (aged) than the rear HO2S (HO2S-12 is lazy).Click here to see.

Jan 16, 2013 | 2005 Buick LeSabre

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The vsc light and the trac off light and check engine light all came on at the same time code p0420 comes up on my 2005 highlander what does this mean?


A p0420 sets after Engine and catalyst are warmed up, vehicle driven within set vehicle engine speed range and waveforms of heated O2 sensors bank 1 sensor 1 and bank 1 sensor 2 have the same amplitude.
Catalytic convertor and O2 sensors need to be tested

Apr 24, 2011 | 2005 Toyota Highlander

1 Answer

Getting P0420 code & P0303 code...why?


A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for
  • An oxygen sensor is not reading (functioning) properly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible SolutionsSome suggested steps for troubleshooting a P0420 error code include:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2), replace if necessary
  • Replace the catalytic converter

Code p0303 means one cyliner is misfireing. Check spark plugs and wiring cables. If one cylinder isn't working good that could be the possible couse for the first code P0420 and all other engine problems.

Feb 25, 2011 | 2005 Isuzu Ascender

2 Answers

Check engine light on, code reads p0420


Hi and welcome to FixYa!

Code p0420 means Catalyst System Efficiency Below Threshold (Bank 1). This will surely needs attention to resolve the problem.

Hope this helps and thank you for using FixYa! Have a good one!

Jan 26, 2011 | 1999 Buick Century

1 Answer

I have a 2003 Ford Escape with a PO420 error code. When I accelerate, it sounds like air is coming from my engine. What is the problem and what should I do?


Here's what the code means, P0420 -- Catalyst System Efficiency Below Threshold (Bank 1).
Causes: Bad O2 senor, bad catalytic converter, and/or leaking exhaust manifold.


The error is coming from the O2 sensor number 1 between the exhaust manifold and the catalytic converter. The sensor itself may not be the problem. From what your describing is maybe a leak coming somewhere near the exhaust manifold. This would set off the P0420 code. Look around the exhaust manifold down to the catalytic converter for leaks that will leave black marks from burned fuel. If this can't be easily found, you may have to take the car in and have the exhaust hooked up to a smoke machine. This will inject smoke into the tail pipe and any leaks will be found by the smoke coming out of it.

Nov 16, 2009 | 2003 Ford Escape

2 Answers

Engine check light read p0171 and p0420, noticed a leak of engine oil on cylinder 2 area of head gasket when checking the sparks plug, is that the cause?


P0171 code is described as: lean condition bank 1, oxy sensor 1. If your vehicle is a 4 cylinder, which I believe it is.. you have got a lean air/fuel mixture being found by the ecm(computer).This can be caused by several things. The first of which is a possible vacuum leak at or near the intake manifold. This can also be caused by a MAF(Mass Air Flow) sensor problem or even by something as simple as a clogged fuel filter. This lean condition could also be the cause of the P0420 :described as a catalyst efficiency problem. It would be best to have the vehicle taken to a reputable repair facility that is capable of engine performance diagnostics and have them run tests for these codes. The gasket you mention is most likely a valve cover gasket not the head gasket and would not cause these codes. Although you should have this leak fixed before it becomes a problem.

Hope this helps..

Apr 20, 2009 | 2003 Toyota Camry

1 Answer

2001 chevy impala has a P0420 code and a check engine light that will not reset. Earlier P-codes indicated a problem with cylinders 1-3. these codes reset after a while. Found intake vacuum house off on...


A code P0420 may mean that one or more of the following has happened:

An oxygen sensor is not reading (functioning) properly
The engine coolant temperature sensor is not working properly
Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
Retarded spark timing

Apr 04, 2009 | 2001 Chevrolet Impala

1 Answer

Code P0420


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter

Mar 24, 2009 | Chrysler Concorde Cars & Trucks

1 Answer

Ford windstar OBD II code P1537/38, P0171 and P0420


It could all be related.P1537/38 are the intake manifold runner controls are stuck open.They are controlled by vacuum solenoids.The P0171 is bank one of the engine is running lean,usually caused by a vacuum leak, P0420 is catalytic converter efficiency code. The computer monitors the switch rate of the front 02 sensors and compares it to the switch rate of the rear 02 sensors to tell if catalytic converter is doing its job. Now if the front 02 is not switching properly then this will cause this test to fail and set this code.
Look on bottom section of the intake manifold at the back of engine(where tranny bolts up) you should see the vacuum motors there on the intake,these are the control motors for the intake manifold runners.Make sure the vacuum lines are hooked up and lines are not leaking. Also you will see a lever from it to intake make sure they move and are not binding.

Mar 11, 2009 | 1996 Ford Windstar

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