Hi At a crossroads with this car, sold by local car dealer, to a friend of mine! mil came on soon after she took delivery, it said map sensor fault, checked sensor indeed faulty so renewed all ok, i did notice that throttle response was slower after the sensor was fitted but i assumed that it had been a little rich before maybe, it went for a few days and light came back on, had car in and read code po420 catalytic convertor aged/ poor efficiency, selling dealer pulling faces at possible convertor fault so i fitted a pre cat lambda at his request. sure enough 2 days later light back on same code, this time i looked deeper off my own back ie dealer whinging but i ignored him and carried on as she is a friend. noticed that both lambdas switching together in almost prefect unison. This to me said faulty cat esp with regard to previous fault with map and the fact the car dealer has his own obd 2 tool from halfords and had already reset the light before selling the damn car!. So i renewed the cat with a good quality one from ces and the readings were as normal pre cat switching post cat hardly switching and reacting to sudden throttle opening, im not sure tbh quite how fast the post sensor should react but it lasted a week which is 200 plus miles in her commute before coming back on,

i have scanned as much as my scanners will allow looking for errors but it runs well and all seems ok, Passes emmisions test with no problem at all with normal readings for this type of vehicle.My question is, as i understand it this is a euro 5 code/obd2 and it stems from the management doing periodic emmisions checks at certain driving conditions etc and flags said code if it feels there is a breach and the mil stays on as your supposed to get the fault cured as its emmisions related to save the planet etc. so the fault could then be intermitent and brief? could the maf cause this perhaps in view of change in throttle response although readings seem normal to me cant think what they were as i sit here at home but im sure they looked about right.?

im stuck she wants it fixed the dealer dont wanna pay for what we have already done saying cat not needed!despite the fact it clearly did and is trying to put the onus on us to fix without it costing them!

Also is it worth changing the post cat sensor although from what i can see it does switch.

scoping the lambdas also shows the same reactions to the scanner readings too. the coolant temp reads fine the only thing i cant seem to scan is the fuel trim.

regards

Marino (maz)