Catalytic Converter Glowing Red Hot

Is your car running rough, the engine shakes, and the catalytic converter seems too hot and glows red?

Check engine light on catalytic converter glowing red hot

Your check engine light should be on, too, and if you read the codes, you will find an engine misfire fault code.

The car feels like it has lost power; you notice poor fuel economy, poor performance, and inadequate throttle response. You open the hood and see the Catalytic Converter Glowing Red

In this article, we will discuss the most common problems causing the catalytic converter or exhaust manifold to overheat. 

If the catalytic converter is glowing red hot, the first thing that most people think is that the catalytic itself is clogged, but that is not always true. 

Bad catalytic converter

We had seen cases when a mechanic changed the catalytic converter, thinking that it was clogged because it glows red. While that is possible, if the catalytic converter is glowing red hot, it doesn't always mean that the catalytic converter is bad. 

We have seen cases that after spending several hundred dollars on a new catalytic converter, the new catalytic converter is still overheating. Those problems are caused by an underlying engine problem, which sends unburned fuel to the catalytic converter. 

Why is my Catalytic Converter Red/Hot? 

Sure, one possibility is that it can be clogged.

Another common reason why a catalytic converter glows red is that raw fuel is getting into the catalytic converter and is getting burned there. For example, if you have a cylinder misfire due to a bad spark plug or ignition coil. 

What causes a catalytic converter to glow red hot? 

Here, we will discuss some of the most common reasons why a catalytic converter may be glowing red. 

Misfire / Bad Spark Plugs

Catalytic converter glowing red hot due to bad spark plug

If the spark plugs are too old, they may be causing the misfire. The spark plug gap may be too large, or the resistor inside the spark plugs is damaged, and now they no longer ignite or burn the fuel that goes to that cylinder. When this happened, you will get a cylinder misfire code.  

Your check engine light comes on, and if you scan the OBD-II codes, you will find out that you have one or more of the following systems:

  • P0300 Random/Multiple Cylinder Misfire Detected
  • P0301 Cylinder 1 Misfire Detected
  • P0303 Cylinder 3 Misfire Detected
  • P0304 Cylinder 3 Misfire Detected
  • P0305 Cylinder 3 Misfire Detected
  • P0306 Cylinder 3 Misfire Detected
  • P0307 Cylinder 3 Misfire Detected
  • P0308 Cylinder 3 Misfire Detected

If you are wondering how to diagnose the check engine light, read our article on Check Engine Light. 

Once you confirm that you have an engine misfire, your first step is to replace the spark plugs, especially if they have never been changed.  

Bad Ignition Coil

Catalytic converter red hot due to bad ignition coil

Ignition coils fail, and on some car models (Audi / VW, anyone?) more frequently than they should. 

The first thing you should do is to swap the ignition coil on the cylinder that is causing the problem with one that is not. So if you are getting a P0302 code, that means Cylinder 2 is misfiring and causing the catalytic converter to overheat. 

Remove the ignition coil from cylinder two and swap it with one that you know is not the problem, let say Cylinder 4. Before you restart the car, clear the codes using an OBD II code reader. 

If you are getting P0304, the problem is moved to cylinder 4, so the ignition coil is the problem. If you are still getting a P0302 cylinder misfire, that means the problem is not the ignition coil, so we need to continue troubleshooting cylinder two misfires. 

If you determine that the issue is a bad ignition coil, replace the coil. You don't need to replace all of the coils. Replacement ignition coils can be purchased online for any make and model.

Engine Control Unit 

It is not uncommon for the Engine Control Unit (ECU) to fail, causing an overly rich fuel mixture. Don't rush to replace the ECU, though. Often the engine wire harness can be the problem. 

ECU is easy to replace but requires programming by the dealer, and ECUs are expensive. The wire harness parts are less expensive, but they need over 10 hours of labor to replace most cars. While a lousy ECU or wiring harness can cause an engine misfire, resulting in catalytic converter overheating, such issues don't occur very often. 

Fuel Issue

Power loss and red hot catalytic converter caused by a bad fuel pump

You are also having fuel issues, especially if you experience power loss and a red hot catalytic converter.

You may have excessive fuel pressure due to a failed fuel regulator or even a damaged fuel injector. 

If you suspect that your problem is fuel related, you can perform a fuel pressure test. On most cars, there is a fuel pressure test port on the fuel rail. Plug a fuel pressure gauge and measure the fuel pressure. 

Burned or Bent Valves or Worn Rings

This is the worst-case scenario, and hopefully, not your case. But if you have any burned or bent valves or worn out rings, there will be no compression at that particular cylinder. 

In return, the fuel/air mixture is not getting burned. The raw unburned fuel goes out the exhaust pipe and is getting burned up at the catalytic converter. 

This is typically a costly repair, and you will most likely need a mechanic's help to fix such issues. 

Other Problems

The list of problems that can cause your engine to run rich can go on and on. 

Other problems could be, MAF sensor problem, oxygen sensor problem, spark plug wire short. If you have an older car, the distributor and spark plug wires could be the problem.

The ignition coil electrical socket can also get loose or even get unplugged from the ignition coil or pack. 

On some cars, oil could between the ignition coil and spark plug due to a valve gasket oil leak. This can cause a short and, therefore, an engine misfire. 

When this happens, the engine will shake excessively, and raw unburned fuel will reach the catalytic converter and get burned there, causing the "cat overheating."

What should I do if my catalytic converter glows red hot? 

what would cause my catalytic converters to glow

Before you decide to change the catalytic converter, perform a couple of tests to determine if the catalytic converter is clogged. One standard test is used to determine if the catalytic converter is clogged to do an exhaust backpressure test. Any muffler shop can do a back pressure test, but you can do this yourself as well. 

This test is straightforward. Get an Exhaust Back Pressure Tester Gauge. Unplug the upstream oxygen sensor and plug the gauge—Startup the car. Within minutes, you will see if there is excessive pressure building up in the catalytic converter.  Rev up the engine and hold the RPMs in 2000.

In most cases, the pressure should be less than 20 kPa. 

Catalytic converters are designed to operate at very high temperatures. The standard operating temperature can range between 1000 -1500 degrees F. 

Catalytic converters can handle minuscule amounts of raw fuel, but not a significant amount of fuel can make it to the cat due to a misfire.

Diagnose catalytic converter glowing red hot


If you have an engine problem, the check engine light is on. Read the fault codes with an OBD-II scanner via the diagnostic port under the dashboard. 

Can I drive if my catalytic converter glows red?

No. We would not recommend driving a vehicle if the catalytic converter is glowing red. Call an auto mechanic or dealer and ask for the next step. 


If your catalytic converter is glowing red hot, have the vehicle diagnosed immediately. Do not ignore this problem, or you may cause expensive damage to the engine. 

You have a problem with fuel not burning, engine running rich, but you will damage your catalytic converter if you continue to drive this way. The converter is not going to last very long. The honeycomb material inside the catalytic converter will melt, clogging your catalytic converter. You may cause further damage to the engine itself.