Hi all
the little skoda failed its MOT by the skin of its teeth. excess CO.
I replaced the pre-cat lambda probe (had to grind it off and get a socket on it directly as none of lambda sockets slipped and the crows-foot snapped).
no improvement in diagnostic readings and a test of channel 46 results in CATB1 NOK and P0420.

Is this a new mani-cat situation? I can't see any cracks.

thanks
Justin

Sons 1.2 just passed but had leak in exhaust system. The MOT guy who I know sealed leak and got it through Check for any leaks and perhaps replace post cat lamda.

Alasdair

Why would the post cat lambda have any impact? By then the job is done, no?

The trim levels are showing -12 so it feels like the car is running far too rich. The evap valve is solid, coolant sensor looks ok but am replacing it, injectors are not leaking but I'm also replacing those in case the springs are weak. No misfiring so sparks are likely to be ok. Timing is showing no material adaptation. Fuel rail pressure is top end at 4.3 bar which might be playing a part. Might also be the PCV valve.

I don't think the cat is actually the problem. The short term trim suggests the engine is running mighty rich and perhaps the ECU can't trim enough to make the difference.

Might change the map sensor but the manifold pressure looks squarely within normal ranges.

Sorry your right a bad downstream 02 sensor sometimes causes p0420 as ecu gets confused but wouldnt cause rich running. Is the fuel rail pressure too high at top end 4.3 bar. My sons from memory 1.2htp is around 3bar. Could also be as you said PCV valve or carbon canister is full/clogged

Alasdair