Catalytic Converters: Efficiency Code Diagnostics

Catalytic Converters: Efficiency Code Diagnostics

Understanding catalytic converter efficiency codes can be a long road to a happy customer or an expensive comeback.

Understanding catalytic converter efficiency codes can be a long diagnostic road that can either lead to a happy customer or an expensive comeback. Chances are the original converter didn’t fail on its own, but conditions upstream hastened its demise. 

Almost every part on the engine determines how long the catalytic converter will last. It could be a faulty line of computer codes that pulses an injector too long or it could be a stuck piston ring allowing oil to be sucked into the combustion chamber. These little details can limit the life or efficiency rating of a catalytic converter. 

The Code

For a catalyst efficiency code to be set, a number of criteria must be met. The specific enabling criteria is different for almost every vehicle. For a code to be set, the oxygen or air/fuel sensor and the rear oxygen sensor must see a reduction in the efficiency of the converter. In other words, if the oxygen levels before and after the converter do not change, the converter is not working. 

But, this is not an automatic pass or fail. The oxygen sensors need to see this loss in efficiency over a number of drive cycle conditions. This is why it might take a few hours or a few days for the light to come back on after a code is erased. 

 On most vehicles, an efficiency code will not be set if an oxygen sensor heater code or any oxygen sensor-related code is set. Even if the converter is operating below 95% efficiency or the oxygen sensor is bad, the chances of the light coming right back on are slim. 

What is Efficiency?

The converter has an efficiency rating that is computed by the vehicle. This number rates the amount of reduction that is occurring in the converter and its ability to store oxygen. But, the efficiency of the converter is tied to the fuel trim of the engine. Most engines minutely alter the fuel trim to replenish the oxygen in the converter and to add fuel for reduction. This helps to keep the converter at the correct temperature for the most efficient operation.  

If an engine is running too rich, it cannot store oxygen. If it is running too lean, the reduction process might not occur due to an inability to heat up. If the engine is dealing with a leaking vacuum hose or a stuck injector, it can’t switch the fuel mixture properly to replenish oxygen and reduce harmful contaminates.

Converter efficiency can be checked with some scan tools along with the process of switching between rich and lean. Most converters start out at about 99% efficiency when new, and quickly taper off to about 95% efficiency after 4,000 miles or so of driving. As long as efficiency doesn’t drop off more than a few percentage points, the converter will do a good job of cleaning up the exhaust. But if efficiency drops much below 92%, it will usually turn on the MIL lamp.

You May Also Like

Diagnosing P0420 Or P0430 DTCs with Catalytic Converters

It’s important to understand the basics of catalytic converter chemistry and how catalytic converter failures are diagnosed.

Although modern OBD II technology has simplified catalytic converter diagnostics, it’s still important to understand the basics of catalytic converter operations when dealing with a P0420 or P0430 diagnostic trouble code (DTC). DTCs P0420/P0430 indicate that catalyst efficiency is below predetermined thresholds on cylinder banks 1 and 2, respectively.

Exhaust Repair Options

If a replacement does not meet or exceed the flow characteristics of the original, it could mean more than a loss of power.

Exhaust Manifold Leaks Cause Issues For The Oxygen Sensors

The engine management system does not know there is a crack in the manifold.

Catalytic Converter Theft Crisis – Due to Covid-19?

Catalytic converters have become a hot product among thieves. Has the global pandemic played a part?

Tech Tip: Close-Coupled Converter And Engine Replacement

If an engine breakdown were to occur, debris may be deposited in the converter through engine exhaust ports.

Other Posts

AP Emissions Releases January New Part Number Update

The release includes direct fit EPA converters covering more than 6.6 million vehicles in operation.

Direct Fit Catalytic Converters Features And Benefits

Four qualities stand out the most when looking at these catalytic converters. Sponsored by AP Emissions.

Catalytic Converter Theft (VIDEO)

In some cases, thieves can remove a catalytic converter in less than one minute. This video is sponsored by AP Emissions.

Catalytic Converter Development Process (VIDEO)

Experts discuss the catalytic converter development process from start to finish. Sponsored by AP Emissions.