Petrol with ceramic monolith - 2 years
Petrol with steel monolith - 3 years
Diesel (all steel monolith) - 2 years
Notes and conditions
Catalytic converters should not fail under normal operating conditions. If it has the most likely cause is a problem with the car. The following faults are not covered under the terms of our guarantee.
Impact damage is caused to the catalyst when it hits, or is struck by hard objects. This can cause the monolith to fracture and the pieces to rattle around inside the unit. Possible causes are a hard object striking the converter, hitting speed bumps and off-road driving. Impact damage can usually be seen with the naked eye on the housing of the unit.
Plugged or Contaminated Monolith
This is when the monolith becomes coated and blocked with soot, preventing it from converting the gases that pass through it. This can be caused by the car running rich, using the incorrect fuel or unsuitable fuel additives, and oil or antifreeze entering the exhaust. Excessive levels of hydrocarbons (neat fuel) entering the exhaust can also contaminate the monolith and prevent it working. Always ensure that the vehicle is running at no higher than 55ppm HC before fitting a new catalyst *.
Melted or Broken Monolith
Monoliths can be broken in a variety of ways, the most common being impact damage (see section above). It can also be broken when it suffers a sudden drop in temperature (e.g. driving through a ford) as the steel shell contracts faster than the ceramic monolith as it cools and crushes it. The monolith can be melted when unburned fuel is injected into the catalyst. Causes of this are tow or bump starting, or the carís engine not firing properly on starting. More information on the causes of melting monoliths can be found below.
There are many problems that can cause a catalyst to overheat or fail. The most common of these is when unburned fuel enters the catalyst. This fuel ignites when it reaches the catalyst because of the high operating temperatures, causing the catalyst to superheat and melt down. Some causes of this are faulty spark plugs and leads, which cause the engine to misfire, and a badly timed distributor.
The oxygen (lambda) sensor collects and sends information to the ECU (Electronic Control Unit). This is used to control the air/fuel mix. If the oxygen sensor is faulty, the air/fuel mixture will not be corrected. In the case of it running rich excess fuel will enter the catalyst, causing it to superheat and melt down. It is advised that a new oxygen sensor is fitted every time a catalyst is replaced.
Fuel Injection Systems
A catalyst can be damaged if a fuel injector is leaking internally or dribbling fuel into the engine. The excess fuel will then enter the exhaust system and superheat the catalyst, causing the monolith to melt down.
Map sensors inform the ECU of the load on the engine and the amount of air entering it. If this sensor fails it causes a rich condition in the engine, which can superheat the catalyst and cause it to fail.
A worn or defective carburettor can cause a catalyst to overheat. Problems such as improper float or air/fuel mix adjustments and worn metering rods can damage the catalyst. The choke system also needs to be operating properly so the right level of fuel enters the system. If too much fuel enters the system the catalyst will overheat and eventually fail.
Canister Purge Valve Control
This vacuum operated valve vents fuel vapour from the carburettor bowl to the charcoal canister. If the vacuum is breached, the charcoal canister will flood and the air/fuel mixture will become very rich. This excess fuel will enter the catalyst and the monolith will melt down.
A catalyst should not be considered to be a silencer although it does have some silencing qualities. Noise can be caused by excessive amounts of fuel getting into the converter.
* We will no longer accept emissions warranty returns without the relevant emissions report. We will also not collect any catalysts for warranty claims with HC levels above 60ppm, except at the discretion of the technician.