Technical 16 www.aftermarketonline.net DECEMBER/JANUARY 2026 Exhaust paste becomes brittle when dry and can break off Nottingham-based components manufacturer offers advice for workshops in understanding and tackling emissions tech Around 2 million MOTs were expected to expire in December — a near 30% increase from the same period five years ago and 8% up on last year’s figures — and emissions control issues are often among key challenges facing motorists and technicians. BM Catalysts, a leading manufacturer of aftermarket hot end emissions products, says its mission of supporting garages and technicians includes advising on what can lead to a failure if existing or other aftermarket parts are insufficient. The leading European manufacturer of aftermarket hot end emissions products says it recognises the importance in emissions tech education. Control devices allow harmful emissions gases made up of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides to pass through the complex precious metal ladened internal monolith. A chemical reaction takes place converting the harmful gases into a mixture of water, carbon dioxide and nitrogen. During an MOT inspection, a vehicle undergoes a routine emissions test. If the vehicle fails, the blame usually lies with the CAT or another emissions control device. However, it is important to note that the device can only convert the gases that are passed through it. If the vehicle in question is running poorly, the device becomes contaminated with unburned fuel. After a test failure, it is common for the emissions control device to be replaced without fixing the vehicle fault, which often results in another MOT failure later. BM stresses the importance in diagnosing the vehicle fault and preventing another MOT failure. The official reasons for failure are high amounts of HC (unburned fuel), faulty lambda readings and abnormal CO levels. Unburned fuel entering the device is caused by a number of factors, such as faulty spark plugs, a faulty fuel injection system and misaligned distributor timing. Faulty lambda sensor readings are caused by a faulty lambda sensor itself or faulty MAP (manifold absolute pressure) sensor. Another common malpractice is the use of exhaust paste. Due to the extreme heat of the device the paste becomes brittle when dry and can break off. If this dry paste hits the internal monolith, it can cause breakages and fractures, leading to incorrect amounts of harmful gases exiting the emissions control device such as CO. However, if the emissions control device itself is at fault, BM strongly recommends using a new fitting kit as a small investment that prevents big problems. Worn gaskets, perished rubbers, and rusty fittings can all cause leaks, excessive movement, or even damage to new units — risking warranty issues and potential costly, repeated replacements. Technicians are encouraged to fit new gaskets and other components every time. BM boasts a range of over 3,000 CATS and other products catering for 90% of the European vehicle car parc. Garages and technicians can use the firm’s free online learning platform, Garage Pro, for advice on the fundamentals of all emission control products, standards and more. Visit https://bit.ly/ bmcatsproducts to find out more. Beyond the tailpipe
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