Catalytic converter (Audi A4 B6)

The catalytic converter has a central ceramic part of a honeycomb structure "3" covered with a carrier layer. On the carrier layer are salts of noble metals acting as converters. The catalytic converter is fixed in the housing "1" by means of an insulating support layer "2" that simultaneously compensates for the thermal expansion of the catalytic converter (see illustration Location of injection system components in the 2.5L diesel engine compartment).

Petrol engines

In order to reduce harmful emissions with the help of a catalytic converter, the injection system must precisely dose the amount of injected fuel required for combustion. The lambda probe is located in the inlet pipe before the catalytic converter and is washed by the flow of exhaust gases. The lambda probe is an electronic sensor that measures the oxygen content in the exhaust gases and represents it in the form of voltage fluctuations. Information from the lambda probe is transmitted to the injection system control unit. The obtained value allows you to adjust the composition of the air-gasoline mixture. On the one hand, this is necessary, since operating conditions are constantly changing (idle, full throttle), on the other hand, since optimal afterburning of fuel in the catalytic converter occurs only in this case if the exhaust gases contain a sufficient amount of fuel.

In order for the fuel to be burned in the catalytic converter, a temperature of 300-800°C is required. This requires a higher fuel content in the mixture than for clean combustion.



The catalytic converter of a gasoline engine is a so-called three-function device. In the controlled conversion process, carbon monoxide (CO) and hydrocarbon (HC) are oxidized, and the concentration of nitrogen oxides (NOx) is reduced.

Safety precautions to avoid damage to the catalytic converter

To avoid damage to the lambda probe and catalytic converter, the following requirements must be met:

Petrol engines

• Be sure to use only unleaded gasoline.
• Starting a warmed-up petrol engine by pushing or towing is permitted only in one attempt and at a distance of no more than 50 m. It is better to use a jumper cable for this purpose. Unburned fuel during ignition can lead to overheating of the catalytic converter and its destruction.

Warning: Starting vehicles with AT towing is not possible.

• If you have difficulty starting the engine, do not engage the starter for too long. This will cause continuous fuel injection. It is necessary to identify and eliminate the cause of the malfunction.
• If there are problems with the ignition system, when determining their nature, it is necessary to exclude fuel injection when the starter is turned on. To do this, disconnect the fuel pump relay.
• Never empty the fuel tank completely.
• If misfiring occurs, do not increase engine speed and correct the problem immediately.
• Use only recommended spark plugs.
• Do not perform spark testing with the spark plug connector disconnected.
• It is not allowed to check the operation of the cylinder by disconnecting the ignition wire from its spark plug. In this case, unburned fuel gets into the catalytic converter.

Petrol and diesel engines

• Do not park the vehicle over dry leaves or grass. The exhaust system in the area of the catalytic converter is very hot and radiates heat even after the engine has stopped.
• Do not apply underbody protection products to exhaust system components.
• It is not permitted to change the design of heat shields.
• When filling the engine with oil, pay special attention to never exceeding the level indicated on the indicator as Max. Excess oil due to incomplete combustion enters the catalytic converter and can damage its alloy metal coating or completely destroy the catalytic converter.

The original article is located on the online resource AUDIMANUAL.ru