How to Fix a Catalytic Converter (Without Replacing It)

catalytic converter inside
The matrix of this catalytic converter is embedded with precious metals to reduce harmful emissions.

The RedBurn / Wikipedia

The catalytic converter is part of the exhaust system, processing all exhaust leaving the engine before it can escape into the atmosphere. A bad or clogged catalytic converter can ultimately lead to engine failure, so it's important to address the issue promptly. However, having catalytic converter problems doesn't necessarily mean that the converter has to be replaced. You may be able to fix your catalytic converter without replacing it using one of the following methods.

How Catalytic Converters Work

Today’s automobiles are cleaner and more powerful than ever before, thanks in no small part to electronic controls and emissions control devices—including catalytic converters. In your engine, fuel combines with oxygen in the air, set off by a spark or the heat of compression. Ideally, this chemical reaction would result in only motive energy, water vapor (H2O), and carbon dioxide (CO2). However, In real-world driving conditions, the ideal is difficult to achieve, resulting in harmful emissions.

The catalytic converter uses precious metals and high heat to oxidize and reduce harmful emissions, converting them into safer compounds like H2O, CO2, nitrogen (N2). Because of the way they are constructed, using rare metals like platinum, palladium, and rhodium, catalytic converters are expensive, costing upwards of $1,000 (not inclusive of diagnosis and installation).

Signs of a Catalytic Converter Problem

  • Engine accelerates poorly or is hard to start. These issues could indicate a clogged catalytic converter, restricting the flow of exhaust out of the engine. A clogged catalytic converter essentially "suffocates" the engine, preventing it from "exhaling" the exhaust.
  • A sulfur or "rotten egg" smell indicates the formation of hydrogen sulfide (H2S), a likely sign of catalytic converter contamination. Ammonia (NH3) odor may also indicate poor catalyst function.
  • If the catalytic converter's housing is discolored or warped, there may be internal leakage or overheating.
  • A rattling noise when starting the engine might indicate a broken catalyst.
  • Failing the annual or semi-annual emissions test might also be linked to a failed catalytic converter.
  • Vehicle warning lights. An illuminated check engine light or malfunction indicator lamp (CEL or MIL) with a catalytic converter diagnostic trouble code (DTC) is the most common catalytic converter problem indicator. If the engine control module (ECM) detects a catalytic converter problem, it might record DTC P0420, defined as “Catalyst System Efficiency Below Threshold.”

The "Italian Tune-Up"

The "Italian Tune-Up" is a common fix for a range of automotive problems, including a clogged catalytic converter. Many drivers simply don’t push their vehicles hard enough to heat the catalytic converter to its most-efficient temperature—between 800 °F (426 °C) and 1,832 °F (1,000 °C)—leading to premature failure.

Running a vehicle harder than usual for a few miles (e.g. multiple hard accelerations) may heat up the converter adequately and burn off performance-robbing deposits in the intake, cylinder head, exhaust, oxygen sensors, and catalytic converter.

Fuels and Fuel Additives

A different fuel or fuel “additive” may be effective at cleaning out catalytic converter deposits. For example, if you typically fill your vehicle with the cheapest low-octane fuel, try running your vehicle on a few tanks of high-octane fuel.

Adding one gallon of lacquer thinner to ten gallons of gas at your next refuel may also be effective clearing out catalytic converter deposits. You can try either of these methods in combination with the Italian Tune-Up method.

Engine Running Right

You may need to fix other engine problems in order to solve your catalytic converter problem. A lazy oxygen sensor might falsely indicate a catalytic converter problem, yet not set a DTC for itself. A technician can determine if the sensor is responding as it should.

Other engine problems, such as fuel trim running too rich or too lean, oil or coolant burning, or engine misfire problems could all lead to catalytic converter contamination or premature failure. Depending on the extent of the damage already done, fixing engine problems might save the catalytic converter from a meltdown.

Fixing Exhaust Problems

Exhaust leaks are common and can skew oxygen sensor readings without setting other DTCs. A careful search might reveal exhaust leaks that, when repaired, “restore” catalytic converter function, at least from the point of view of the ECM.

Worn exhaust gaskets and corroded flex pipes are two common issues that are significantly less expensive and more effective than replacing a catalytic converter.

Cleaning the Catalytic Converter

Removing and cleaning the catalytic converter is another potential fix. After removing the catalytic converter, use a pressure washer to blast out any contaminants from the matrix. Be sure to flush the unit from both ends.

Another way to clean the catalytic converter is to soak it overnight in a combination of hot water and degreaser or laundry detergent. This process takes longer but is necessary to dissolve the deposits clogging up your catalytic converter. After washing or soaking, be sure to dry the catalytic converter completely before reinstalling.

Make Your Catalytic Converter Last Longer

Sometimes, the catalytic converter absolutely needs to be replaced (like if it's broken internally or melted down). If you have to replace your catalytic converter, make sure it lasts as long as possible with these tips.

  • Cars like to be driven. Don't let your car sit for weeks without being driven, and make sure you take a few long drives rather than only short trips. To reach proper operating temperature, spend at least 20 minutes driving at highway speeds once a week.
  • Keep up with regularly scheduled maintenance, like oil changes, air filter changes, and regular inspections. If you or your technician see anything that needs care, address it right away to prevent possible damage to the catalytic converter.
  • Address the check engine light promptly. If the MIL illuminates, it's likely that the engine is running in open loop, based on programming and not feedback. In open loop, the engine may run too rich or too lean, which can be damaging to the catalytic converter.
  • Consider switching to high-octane fuel, at least periodically, if you find that changing to high-octane fuel fixes your catalytic converter problem. The initial change cleans out the catalytic converter, but a permanent switch could maintain it for the life of your vehicle.