Absolutely, the cat is poor. There is nothing wrong with the lambda sensor. A reading of 1.00 is perfect, it cannot be any better.
You could maybe try some Cat-a-clean, as your CO is only a little out of range. Some say it works, others it doesn't but its a cheap fix if it does.http://www.cataclean.com/
The MOT lambda value has nothing whatsoever to do with the operation or condition of the car's lambda sensor! If you're really a mobile mechanic it might be an idea not to advertise your lack of understanding of the subject in a public forum.
As I said in a similar post, a LOT of misinformation on here. For the benefit of those who seem unable to grasp simple diagnostics let me explain.
The reading of the Lambda sensor is an indication of the fuel to air ratio within the engine. In an ideal world 14,7 parts of air are required to burn effectively 1 part of fuel. So, to make it simple this 14.7 to 1 ratio is known as lambda 1. The reading in this case is 1.00 which is showing the fuel air mixture is correct and the ECU and lambda (oxygen) sensor are working correctly adjusting the fuel from rich to lean approx once a second or so.
During the burning process other gases are produced including hydrocarbons and carbon monoxide. If the system was running let's say too rich, then there would be more hydrocarbons. The lambda sensor will detect this and the reading will drop to around 0.9 maybe. Conversely, if the mixture was too lean the reading will go up to perhaps 1.4. The ECU will try to correct this but it has a fixed 'map' programmed into it and so is limited. When the reading is out of limits for too long or by too far the engine management light will be triggered and a fault code such as P0170 will be logged. P0170 - fuel trim malfunction.
During the burning process in the engine it is impossible to get every molecule of fuel burnt totally so there are some by products which are considered noxious or undesirable. Carbon monoxide is a dangerous gas and although only a small amount is produced of the total waste product, it is removed from the exhaust by a catalytic converter. This breaks down the gas so that it exits as a mix of water and carbon dioxide. Carbon dioxide is the gas associated with greenhouse gases but as a gas is less dangerous to us than carbon monoxide sometimes known as the silent killer.
So, in this case posted here, the readings show a high carbon monoxide reading of 39. In order to diagnose the problem, the other readings MUST be taken into account. With hydrocarbons at 40, which is well below the limit, and a lambda reading of 1.00, this indicates that the fuelling through the engine is pretty good and the ECU and lambda sensor are working together correctly. Therefore, by elimination, the only reason the carbon monoxide reading is too high is because the catalytic converter is not doing its job and breaking down the exhaust gases efficiently.
In a petrol engined car made from 2001, there are usually 2 lambda sensors, number one before the catalytic converter known also as the upstream one and the second lambda sensor also known as the downstream sensor fitted after the catalytic converter. The cats fitted in these cars are 3 way converters in that they remove the hydrocarbons, carbon monoxide and the nitrous oxides. If the cat is failing then an engine management light will be displayed and the fault code may well be P0420 - cat efficiency below threshold.
Before replacing the cat, a gas emission test is done and a diagnostic check using proper equipment. The gas emission test may well show a CO reading that is well within the MOT limits but the ECU is detecting a slight malfunction. This is then checked by watching both lambda sensors at the same time. Once the engine is hot and the cat is lit, that is, up to operating temperature (3 mins at 3,000rpm), the reading on your average upstream sensor will 'switch' (change) from around 0.1v to 0.8v around once a second or so - some new type sensors do not operate like this - and the downstream sensor should be fairly stable around 0.6v. This would indicate the cat is okay and doing its job. If this is the case then the ECU map is reprogrammed to accept larger tolerances.
If the downstream sensor was also switching similar to the upstream, then this does almost conclusively show the cat has failed if the rest of the system is operating correctly. It should also be noted that cats are lifed to just 50,000 miles so anything after that is a bonus. Also, particularly in Fords where the cat is close to the exhaust manifold, a misfire will cause unburnt fuel to hit the cat's honeycomb section and destroy it. And, as most of us know, the coil packs on Fords are prone to failure causing misfires which will eventually harm the cat.
And so, to the donkey who questioned my previous post, I suggest you do some Wiki reading if the above is beyond your comprehension which it surely is or you wouldn't have made yourself look a right pillock with your complete lack of knowledge and ignorance.
Probably a complete waste of time trying to educate you, but here's hoping....I wont hold my breath though.