CLIVEJD Posted May 30, 2009 Share Posted May 30, 2009 Hi all Some time ago my Focus 1.6 LX developed a fault. The amber engine warning light illuminated and my fault reader gave a P04020 error code. My local garage has replaced the cat, the forwardand rear lambda sensors, temperature sensor and the fuel regulator. These were replaced (on fords recomendation) separately but on each occasion the warning light again came on again after about 50 miles. The light is again on now, the error code is the same as on previous occasions but we are running out of options and parts to replace. The following info came from my memoscan Fault Code - P04020 Generic Catalyst efficiency Below Threshold (Bank 1) Freeze Frame info trouble code - P0420 Fuel SYS1 CL, faulty HO2S Fuel SYS2 CL, faulty HO2S calc laod 56% coolant 112 deg C ST FTRM 1 -3.1 LT FTRM 1 -6.2 MAP (Kpa) 0 engine RPM 2703 Speed 78Km/h Any help with a diagnosis would be greatly appriciated Quote Link to comment Share on other sites More sharing options...
mintalkin Posted May 30, 2009 Share Posted May 30, 2009 The first check is to make sure the second oxygen sensor is giving a steady reading around the mid value, say 0.5v. If this sensor is giving a fluctuating reading, i.e. switching between 0.1 and 0.8v then this proves the cat has failed. The first sensor should always switch when in closed loop but will remain steady on over-run as it goes to open loop, usually at about 0.1v for a second or two.were genuin parts used as aftermarket ones are sometimes not up to the job. also see here http://www.obd-codes.com/p0420 Quote Link to comment Share on other sites More sharing options...
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