Your car’s catalytic converter is located in the exhaust, right after the exhaust manifold.
Its job is to chemically convert harmful exhaust emissions into harmless gases. These harmful compounds are:
- Hydrocarbons
- Carbon monoxide
- Nitrogen oxides
Carbon monoxide is a poison for any air-breathing animal. Nitrogen oxides lead to smog and acid rain, and hydrocarbons produce smog. The catalyst helps to convert carbon monoxide into carbon dioxide, hydrocarbons into carbon dioxide and water, and nitrogen oxides back into nitrogen and oxygen.
The engine computer constantly monitors the performance of the catalytic converter using two oxygen sensors which measure the level of oxygen before and after the catalytic converter. The engine computer compares the signals from both sensors and if it determines that the catalytic converter isn’t performing properly it will illuminate a warning light on the dash.
Without a catalytic converter, or with a damaged one, your car will pump out small amounts of these noxious gases and won’t pass the stringent emission test performed during the MOT.
Replacing the catalytic converter is sadly rather expensive, not least because they contain platinum, which is a very expensive and rare metal. There are between 3-7 grams of platinum-group metals in a standard catalytic converter, and with prices of platinum at £30 per gram you can see why they’re not cheap parts.
In fact the catalytic converter should last life of your car, if it doesn’t it probably means something else, an underlying fault, has caused the failure. The most common problems can be:
- Unburned fuel entering the exhaust – caused by faulty oxygen sensor, incorrect fuel mixture, worn spark plugs or plug wires, incorrect ignition timing, or faulty fuel injectors
- Oil or antifreeze entering the exhaust – possible causes are worn piston rings, faulty valve seals, failed gaskets or warped engine components.
- Fracture of the catalytic converter – caused by road debris striking the converter, loose or broken hangers, or damage due to potholes or off-road driving.
It’s essential to determine the cause of the fault otherwise the new catalytic converter will probably suffer the same fate as the old one.