Petrol Problems

MOT Emission Failure

Screen Shot 2014-09-16 at 16.57.00When a petrol car fails the MOT emissions test there can often be no apparent faults, no engine warning light and no real symptoms. This can make the situation very frustrating for the driver.

Here at Wiseman Motor Services, we have all the relevant knowledge to establish the problem, this can be a faulty catalytic convertor or oxygen sensor.

There may be an air leak in the system that is causing a problem, the cars computer may be doing exactly the correct things to try and correct the air leak.

The first part of the diagnosis is to carry out a thorough emissions test and see what readings are collected. Then by studying these results we can establish a few basic facts

  • High CO (carbon monoxide) can be caused by a faulty catalytic convertor
  • High O2 (oxygen) readings can be caused by air leaks in the induction system
  • High HC (hydrocarbon or unburnt fuel) readings can be caused by worn valve seats
  • Incorrect Lambda readings can be air leaks in induction or exhaust.

Once we have established the problems we can carry out the repairs required to bring the emissions down to the correct levels, and more importantly ensure that the problem does not return. We often see cars that have simply had a catalytic convertor fitted to obtain an MOT pass then fail again next year because the root cause was never rectified.

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