My mini 1.4 petrol has failed on high co and hc but only by a small amount . Last year I gave it a service to pass the emissions but this year it’s not having it.

I have fully serviced it, added a fuel cleaner and used a cleaner through the air intake and to top it off a Terraclean.

There is no sign of leaks anywhere and the exhaust although on 105k miles has no leaks. The Terraclean guy didn’t have a gas analyser so I haven’t had it checked but my obd readings are showing rich. The cat is getting to 750+ degrees and fuel ratio showing 14.6

The car is still recording 51mpg

The terra clean released some performance I had lost over 10 years but I would say the 0-60 is the same as the day I bought it new. The only issue I can say is when driving under load I can hear a kind of pinking noise from the front. It doesn’t appear if I just rev the car at idle, only under load. Any advice? Thanks

  • What does the complete emissions reading look like? I assume your Terraclean operative has refunded you? Sep 24, 2019 at 12:01
  • Possible duplicate of mechanics.stackexchange.com/questions/42985/…
    – GdD
    Sep 24, 2019 at 12:04
  • Pinking under load is the result of the ignition timing too far advanced, which can also make the engine run hotter. Sep 24, 2019 at 14:04
  • Have you ever replaced your upstream O2 (lambda) sensor? Also, 14.6 isn't rich, it's actually lean for a car under normal load and idle. Most vehicles run (from the factory) in the 12.5-13:1 range. Sep 24, 2019 at 14:16
  • So advice for the performance or the fail, or the pinking?
    – Solar Mike
    Sep 24, 2019 at 15:57

2 Answers 2


The best course of action would be the following: Diagnose and resolve the pinking issue as it has the potential to destroy the engine. As mentioned in the comments check to see if the knock sensor is good. Additionally check up and confirm your valve and ignition timings on your car. Also, it will be a good thing to check if you run the correct spark plugs and replace them if they are too old.

After you resolve the above, you could test for emissions only and see if it is alright. If not, we could pick up from there for further diagnosis to fully resolve the issue.


Code P2A53 which you've mentioned in the comments is a generic code but on the Mini platform explicitly relates to the fault with the rear O2 sensors input signal. If you've changed the O2 sensors as you state you have, I'd start checking connectors and loom. Out of interest, with the O2 sensors unplugged, how do the emissions change?

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