What does it mean?

On 1 January 1996 petrol engine vehicles equipped with catalytic converters and
registered after 1 August 1992 became subject to the new CAT emissions test as part of the MoT. Only Green MoT stations may carry out these tests. Those vehicles registered prior to 1 August 1992 fitted with CATs are not subject to the MoT CAT emissions test. There are some vehicles registered during 1993 and 1994 which may not be catalyst equipped.

What does the test entail?

The new test procedure for catalyst equipped vehicles introduced on 1 January
1996 includes a fast idle test as well as the already familiar natural idle test.

Test procedure summary:
• pre-conditioning (oil temperature check)
• fast idle test
• additional pre-conditioning (3 min fast-idle) - if required
• 2nd fast idle test - if required
• catalyst stabilisation
• idle test

Fast idle test:
Emission levels of CO and HC are checked and you must meter
and calculate the Lambda value. The limits applied for each
vehicle model are listed in Department of Trade directives.

Natural idle test:
This check is carried out for CO emissions only. The limits
applied are those specified by the vehicle manufacturer - see
the vehicle model in the applicable Department of Trade
directive.

What does an MoT test station require?

Specialist 4 Gas Class 1 Analyser equipment is required to test catalyst cars from 1 January 1996. However, since this involves a major capital investment (circa £5,000) there is a three year transition period in which test stations may choose whether or not to test catalyst equipped vehicles. Additional equipment will need to be used to determine the cause of failure ie a Lambda sensor/ECU diagnostic code reader/lead detection kit. The type and manufacturer of the 4 Gas Class 1 Analyser required for MoT tests must be approved by the Vehicle Inspectorate which can provide a full list of approved machines.