We're aware that some users are experiencing technical issues which the team are working to resolve. See the Community Noticeboard for more info. Thank you for your patience.
📨 Have you signed up to the Forum's new Email Digest yet? Get a selection of trending threads sent straight to your inbox daily, weekly or monthly!

Will engine warning light cause MOT fail?

Options
2»

Comments

  • Horizon81
    Horizon81 Posts: 1,594 Forumite
    Part of the Furniture 1,000 Posts Combo Breaker
    foofi22 - don't worry. My friend has exactly the same issue. Replaced a cat with a pattern part (as the genuine one was about 3 times the price). Ever since then the Engine Management light is on. I've got a code reader and the code is P0420 which indcated a catalytic convertor fault.

    Basically there's an oxygen sensor before the cat, and another one after the cat. These take readings and should of course provide different readings as the cat filters the bad exhaust gases. The P0420 fault code appears when the readings taken by the 2 sensors are too similar (i.e. indicating the cat isn't working effectively).

    However, this can happen due to slightly different tolerances in the different makes of cat. Of course the car's ECU is programmed based on the original cat. The replacement might not be quite as good however this all matters not one jot, as long as the emissions are ok. So... in my friend's case (as in yours), the emissions are legal and the cat is working fine (just not to the same tolerance as the car's pre programmed ECU).

    In short, it isn't an MOT fail if the emissions are ok. In any case, I'm sure the Engine Management light isn't included in these new regulations. They are only concerned with safety matters like Power Steering lights, ABS lights etc.
  • hazellc
    hazellc Posts: 50 Forumite
    My car's had the engine management light on for the last eight years and hasn't failed an MOT yet. I got my mechanic to check it and he theorised it was something similar. Between the last few cars I've had, a dashboard doesn't look quite right to me if the engine management light isn't on!
  • colino
    colino Posts: 5,059 Forumite
    Part of the Furniture 1,000 Posts Combo Breaker
    Bear in mind that while a lot of aftermarket cats (and sensors too for that matter) are not up to spec and the ecu throws a code because it, after a number of cycles, decides the component is out of range, hence faulty, it may still easily pass the emissions test.
    Equally bear in mind that a lot of P0420 codes are licences to print money, because while they point to a cat fault on a generic reader, it could just as easily be a pin-hole in the exhaust or a joint that hasn't been sealed properly.
This discussion has been closed.
Meet your Ambassadors

🚀 Getting Started

Hi new member!

Our Getting Started Guide will help you get the most out of the Forum

Categories

  • All Categories
  • 350.9K Banking & Borrowing
  • 253.1K Reduce Debt & Boost Income
  • 453.5K Spending & Discounts
  • 243.9K Work, Benefits & Business
  • 598.7K Mortgages, Homes & Bills
  • 176.9K Life & Family
  • 257.2K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 16.1K Discuss & Feedback
  • 37.6K Read-Only Boards

Is this how you want to be seen?

We see you are using a default avatar. It takes only a few seconds to pick a picture.