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Catalytic Converter Warranty

All of our catalytic converters carry a 2 year manufacturers warranty. Although every effort is made to ensure our catalytic converters will not fail, sometimes a problem with the vehicle will cause them to break down. The following problems are not covered by the warranty. 

Road Damage

This is external damage caused to the catalytic converter by hitting solid objects in the road, i.e. speed ramps, large rock etc. If the catalytic converter suffers road damage the monolith inside can be cracked due to it being crushed by movement of the steel can. 

Plugged or Contaminated

Plugged or contaminated catalytic converters are caused by using the wrong sort of fuel in your car. Using leaded or lead replacement fuel will plug up the monolith and cause it to stop working. A similar thing will happen if fuel additives are used that are not suitable for use with a catalytic converter. 

Oil Fouled

This is caused by oil getting into the exhaust system and contaminating the catalytic converter. The most likely causes would be a failing turbo charger, worn engine or oil seals. 

Broken Monolith/Substrate

The use of exhaust paste before a catalytic converter or diesel particulate filter can cause the monolith/substrate to be damaged. When the exhaust paste has hardened small pellets may break away and shoot into the catalytic converter or diesel particulate filter. The monolith/substrate will gradually be destroyed by these pellets and break down. 


There are many problems that can cause the catalytic converter to overheat or fail. The most common causes are below.

a) Ignition System

Faulty spark plugs, ignition coils or HT leads will cause the engine to misfire sending unburnt fuel into the exhaust system causing the catalytic converter to overheat and fail. This will also cause a high HC reading on the MOT emissions test.

b) Oxygen Sensor

An oxygen sensor collects readings and sends information to the electronic control unit. This information is used to control the air/fuel mix. If the oxygen sensor is faulty the air/fuel mix will not be corrected and excess fuel will enter the catalytic converter causing it to overheat and fail. 

c) Fuel Injection Systems
If a fuel injector is leaking internally or dribbling fuel into the engine the excess fuel will enter the exhaust system causing the catalytic converter to overheat and fail. 

d) Map Sensors
Map Sensors tell the electronic control unit the load the engine is under and the amount of fuel entering it. If a map sensor fails it allows the engine to run too rich which causes the catalytic converter to overheat and fail. 

MOT Emissions Test Failure

If a car fails the emissions test due to an under-performing catalytic converter the only reading that will be too high will be the CO percentage.

If the HC level is too high this relates to a poorly performing engine. HC is unburned, or partially burned hydrocarbons. In gas analysis, these hydrocarbons can come from two sources. Firstly, the engine may be worn and passing oil into the combustion chamber, which cannot be fully burned. Secondly, the engine may have developed a misfire, or suffer from only partial combustion of the fuel. This unburned fuel registers as HC on the gas analyser (hydrocarbons, is an indication of unburned fuel exiting the exhaust, the more incomplete the combustion, the higher the HC reading). Please be aware that even though the MOT emissions test allows up to 200ppm for the HC reading any reading higher than 50ppm means that the vehicle has a problem that needs rectifying and the manufacturers of the Cats we supply will not accept warranty claims for emissions failure if the HC level is above 60 ppm.

If a car fails the Lambda test this usually means that either the engine is running very rich or has an air leak. The perfect Lambda reading is 1. A reading lower than 1 shows that a car is running rich. A reading higher than 1 shows that the engine is running lean or that there is an air leak in the system. A vehicle with a high HC reading and a low Lambda reading will almost certainly have high CO but the cause is unlikely to be a faulty catalytic converter.

To instigate a warranty claim for emissions failure you MUST supply a copy of the engine emissions test failure report.

Diesel Particulate Filter Warranty

A DPF is only covered under the warranty for structural failure. 

A blocked DPF is not covered by the warranty as the problem originates upstream of the DPF.

The most common causes of a blocked DPF are listed below.

1. A newly fitted DPF will block if the fault that caused the original filter to block was not rectified prior to fitting the replacement.

2. After installation the main Electronic Control Unit must be readapted to the new DPF. If the correct setup procedure is not completed the regeneration process will not initiate and the DPF will become blocked.

3. A fault with an associated component (i.e. differential pressure sensor, exhaust gas temperature sensor, exhaust gas recirculation valve, fuel vaporiser) will prevent the regeneration process from initiating or completing and the DPF will become blocked.

4. When the DPF light illuminates you must follow the instructions in the owners hand book, failure to comply could result in a blocked DPF.

5. A DPF that uses an additive to assist in the regeneration process must never be driven without this fluid as this could result in a blocked DPF.

6. On most vehicles the regeneration will not take place when the fuel light is on or if there is less than 10 litres of fuel in the tank.

7. The use of the incorrect grade or type of engine oil can cause a DPF to become blocked.

8. It is not advisable to run a DPF equipped vehicle on Bio-Diesel fuel as this can block a DPF.

9. The style of driving or type of journeys covered that do not allow the vehicle to meet the correct parameters for active regeneration will cause a DPF to become blocked. 

Warranty Claim Procedure

If you have reason to believe that the part purchased is faulty you must first complete the Warranty replacement request form located in the Contact Us section of the Website supplying the relevant documentary and photographic evidence as required.