CEL - anyone want to have a guess?

My CEL came on last night when driving home - I'm taking the car to Mark Murphy for a diagnostic after lunch. Just thought I'd post up here to see if anyone can give the correct diagnosis before I get it

Relevant facts are - 01 Impreza WRX, about 5,000 miles since service, decat centre section, Green panel filter, not re-mapped (soon!!), never seen a CEL before in my 3 years driving it, recently switched to E5 (one full tank last week, 40 quid worth of shitty Techron at the weekend when stuck and another full tank of E5 day before yesterday!)

I had never heard about the OBD until I read the manual last night but it seems to say that in cars fitted with OBD the CEL could be a warning regarding emissions????

Any conspiracy theories???

My guess is knock sensor...

My guess is its fooked....

Sell it to froggy for parts & get out and buy an STi - you won't regret it

meant to say it came on steady and has been on since - no flickering/flashing!

Thanks for the suggestion Brian :lol: it's me trying to buy parts from froggy at the moment though :wink:

Why to guess?
You have cel to show you there's an issue - but what sort of you should check with a computer connected.
Or at least trying to get the error code using service connectors (I guess they're also available on new age), to "blink out" the code.

Of course the codes might be sometimes a bit misleading, but anyway they could point you at some direction.

Otherwise it's like reading from the glass ball (mine is broken today )

Ya, I'm getting it checked properly in a couple of hours - I'm not looking for a fix here, just wondering if anyone has a hunch as to what it is!

could be anything john

is the car driving ok? and are you using anymore petrol than usual?

you have to give us a few clues before you plug it in

The car was driving fine and no extra petrol being used I think. Was driving at 2.5k revs in 5th when it came on, only about 5 minutes into the journey.
Have driven it handy since - we'll see what the machine says I suppose

knock sensor had the same prob me self

knock sensor normally intermittent.

a lamda sensor fail pre cat would case this.

Cigar goes to davelegacy!!
The code on the diagnostic was P0420 Catalyst System Efficiency Below Threshold. Mark said it’s a very vague code but possibilities were either of the lambda sensors or the cat itself. He checked out the sensors which are working ok so possibly there’s an issue with the cat. I’m hoping to go de-cat in the near future anyway so no real worries!!

Hi john I have some literature on a mod that can be done the rid of that code if ya want it pm your email and ill send it on to ya I did it to my car while waiting to get mapped and it worked a treat