Symptoms of a Bad Catalytic Converter

Symptoms of a Bad Catalytic Converter
July 30, 2021
Symptoms of a Bad Catalytic Converter

Diagnose Error Codes 0420 and 0430 Yourself

Does your vehicle have a check engine light on, a rough running engine that’s slow to accelerate, and its exhaust smells like sulfur? If so, the issue is probably a bad catalytic converter. An OBDII scanner that reads code P0420 or code P0430 “catalyst system efficiency below threshold bank 1 and/or bank 2”, would confirm that your problem is with the catalytic converter. A catalytic converter can go bad on its own but there could be an underlying issue, as well. Your vehicle could be leaking fuel, coolant, or engine oil which can lead to the exhaust system issues you have now.

OBDII Codes P0420 and P0430

The codes P0420 or P0430 are check engine light codes for problems with your catalytic converter. Your catalytic converter is a honeycomb that works like a filter. Your car creates gases that travel through the exhaust system and the catalytic converter is responsible for eliminating those by burning them off before they make it through the exhaust. When the catalytic converter is broken, this unfiltered fuel byproduct will exit your exhaust and smell like sulfur or bad eggs.

My Check Engine Light Is On And My Car Smells Like Bad Eggs

There are two 02 sensors at the catalytic converter. The one before the converter monitors how well the engine is burning the gas and makes sure that it isn’t too rich or too light on fuel. The 02 sensor after the catalytic converter monitors the efficiency of the catalytic converter. Is it doing its job? Is it burning off the dangerous and foul-smelling engine and fuel byproduct? If not, you might see a check engine light that will read a code 0420 or 0430.

Depending on your car or truck’s make and model, your catalytic converter may be attached directly to your exhaust manifold. If your car is a 4-cylinder it should have one catalytic converter but if you have a V6 or V8 engine, you could have 2 catalytic converters. This is where the difference in code numbers comes in. P0430 is the code you will get when the catalytic converter is attached to the manifold and 0420 is the catalytic converter by itself.

Why Do Catalytic Converters Go Bad?

Aside from having friends that are bad influences, catalytic converters usually do not go bad on their own. Converter failure is usually caused by fuel, coolant, or oil leaking into the catalytic converter and heating it or clogging it. If the issue is caused by one of these your OBDII scanner may tell you that you have a misfire or other issues that could have lead to the bad converter.

Defective Catalytic Converter Symptoms

Check engine light is on.

OBDII Scanner may read code P0420 and P0430: Catalyst System Efficiency Below Threshold Bank 1 or Bank 2

  • The engine may misfire
  • Lowered horsepower, especially at acceleration
  • Your engine is running rough and it idles rough
  • Exhaust smells sulfur or bad eggs
  • How to Diagnose a Bad Catalytic Converter

Check the Air Intake

The air intake system should be checked for leaks. Inspect the air intake tube for cracks, deterioration, and clamps for looseness. If you have scanned your car for codes and there were no fuel-related errors reported, it’s probably not fuel-related.

Does Your Exhaust System Leak

Inspect your exhaust for rusted-out areas, cracks, and deterioration. You should also check the flanges and the gaskets throughout the catback and the catalytic converter connections. Confirm that these connections are tight with no leaks.

DIY Mechanics Note: “Catback” is mechanic slang for everything past the catalytic converter or in the back of or behind your catalytic converter. So your exhaust pipe, resonator (if you have one), muffler, exhaust hangers, and exhaust tips all equal up to your catback. Use this term in casual conversation with your friends that know nothing about cars. They will be quite envious of your automotive knowledge.

Can You DIY a New Catalytic Converter On To Your Car

You can. Absolutely.

Tools Needed ·

  • Ratchet, sockets, and wrenches – sizes vary by make and model
  • Ratchet extensions and joints for the hard to reach bolts
  • A floor jack
  • Jack stands
  • Penetrating oil – this stuff is awesome but you may have to spray it a few times and let it soak
  • Safety glasses for falling debris and rust
  • Padded mechanic’s gloves – you will thank us for this tip
  • Creeper cart if you have access – makes it easier to roll in and out from under your vehicle

How To Replace Your Catalytic Converter the DIY Way

Step 1: Set the parking brake and block the back tires. Using the floor jack, lift the vehicle at the same locations on each side for stability. Secure each point on jack stands. Raise it high enough so you can move around and work.

Step 2: Locate the catalytic converter underneath your vehicle. It’s usually located near the front of the vehicle behind the exhaust manifold. If your vehicle has more than one converter (common on cars with V6 and V8 engines), note the faulty bank that was listed on the OBDII Scanner.

Step 3: Remove oxygen sensors mounted to or near the converter. If there are no sensors to remove, which is rare on cars newer than the mid-90s, move on to step 4.

Step 4: Spray penetrating oil generously on the exhaust flange hardware and flanges. Let them soak for a few minutes. These nuts and bolts are prone to seizing due to dust, debris, rust, and high temperatures. They are exposed to the weather and road chemicals. Expect them to give you a hard time. You may need to spray them more than once and take a break.

Step 5: Check your nuts and bolts for sizes and get the right wrench or socket that fits tight. You do not want a wrench or socket that is loose or has wiggle room. You will round the head of the bolt and create new words when your knuckles hit the car’s undercarriage. We just went back up and added mechanic’s gloves to the tool list after writing that.

The socket extensions and extensions with flex joints may come in handy here. Use them if you find some nuts and bolts that are hard to reach with standard sockets or wrenches.

Once the hardware is removed the converter should come free. It may take a little twist and pull to loosen it up. If you need to, the penetrating oil could help here, as well.

Step 6: Place the new catalytic converter and place new flanges and gaskets to prevent any exhaust leaks.

*DIY Mechanic’s Note*: Make sure the new catalytic converter is the correct one for your vehicle and your engine’s output. Emissions tests and the coinciding regulations may vary from state to state and county to county. Having the incorrect converter may cause you to fail your emissions test. 

Step 7: Install your new and proper catalytic converter by using steps 1-5 in reverse order

*DIY Mechanic’s Note*: When you replace your converter, replace O2 sensors near the converter, too. Save time on future repair costs.

When it comes to catalytic converters or entire exhaust systems, should be your first visit. We have all the parts you need to get your car back on the road and not smell like rotten eggs in no time.

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