Audi A4 Catalytic Converter

The catalytic converter in an Audi A4 is a crucial exhaust system component designed to reduce harmful emissions. It converts toxic gases such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx) into less harmful substances using a chemical catalytic reaction. It is usually located after the turbo or exhaust manifold and works with upstream and downstream oxygen sensors (lambda sensors) to monitor its efficiency.

Typical symptoms indicating a defective catalytic converter include:

• Check engine light activation with an error code P0420 (catalytic converter efficiency below threshold on bank 1).
• Loss of engine power due to partial blockage from carbon buildup.
• Failure of emissions testing caused by increased CO and HC emissions.
• Unusual rattling noises under the vehicle, often caused by broken internal parts.
• Sulfur or rotten egg smells due to obstruction or damage.

Proper diagnosis involves using an OBD scanner to confirm error codes and visually inspecting the catalytic converter for clogging or damage.

Replacement procedures can vary by Audi A4 generation (B5, B6, B7, B8) but generally include these steps:

• Lift the vehicle and remove the airbox and turbo inlet pipe.
• Unscrew nuts and bolts, typically 15 mm size, around the turbo side and midpipe/downpipe.
• Carefully push the catalytic converter backward to free it from studs; penetrating oil may be needed for rusted fittings.
• For specific engine types like B6 1.8T, follow dedicated tutorials for direct replacement procedures.

Using long extensions and proper tools is advised for bolts inaccessible above the transmission. OEM parts cost typically range between €500 and €1500 depending on model and year.

Popular non-road-legal upgrades include:

• Cat converter hollowing out, particularly on B5 models, by drilling and removing the internal substrate to increase exhaust flow. This can improve airflow but results in higher emissions and is illegal on public roads.
• High Flow Catalytic Converters (HFC) for B8/B8.5 Audi A4, A5, and Q5 2.0 TFSI engines. These bolt-on stainless steel converters offer increased horsepower (+27 hp) and torque (+24 Nm) compared to stock units, maintaining sensor and mounting compatibility.

Always check local regulations as these upgrades may not be legal in emission-controlled zones.

Preventative maintenance tips include:

• Avoid engine misfires by regularly inspecting and maintaining spark plugs and ignition coils.
• Use premium-quality unleaded fuel to prevent damage from contaminants.
• Avoid overheating caused by aggressive tuning or faulty engine management.
• Regularly check upstream and downstream lambda sensors to ensure proper air-fuel mixture and catalytic converter efficiency.

Following these steps will help prolong the life of your catalytic converter, usually lasting between 150,000 and 200,000 km under normal conditions.

The catalytic converter is positioned in the exhaust system after the turbocharger or the exhaust manifold. It is equipped with oxygen (lambda) sensors placed before (upstream) and after (downstream) the converter to monitor its catalytic efficiency and emissions performance.

This placement allows the catalytic converter to effectively process exhaust gases while providing real-time data to the engine control unit for optimal combustion management.

Krosfou offers brand-new, original-quality catalytic converters manufactured in Europe with true European E24-103R certification compliance, not just CE marking. Our products use high-grade INOX 409 stainless steel and advanced ceramics with precious metal coatings for superior durability and efficiency.

• Manufactured in Poland by industry-leading engineers and certified by TÜV SÜD Automotive GmbH.
• Guaranteed 3-year warranty covering usage up to 100,000 km.
• Direct factory pricing with free returns within 30 days if unused and unmounted.

These converters meet or exceed all applicable European pollution control standards and are designed specifically for various Audi A4 model years and engines, including Turbo and Quattro variants.

Proper installation is crucial to ensure performance and warranty coverage. Recommendations include:

• Installation by a professional garage specialized in exhaust systems.
• Replacing all associated gaskets, sensors (especially oxygen sensors), and possibly ignition components if misfires occurred.
• Ensuring the vehicle is regularly maintained with correct engine oil and spark plug replacements.
• Avoid starting the engine by pushing or towing and never test engine operation with ignition wires disconnected.

The Krosfou 3-year warranty is limited to product repair at the factory and requires proper assembly invoices. Warranty does not cover damage from negligence or engine faults such as clogged DPFs or ongoing misfires.

Production and shipping lead times are generally 1-6 working days for Europe with express options available.