07 Aygo P0143 Error Code - Lambda O2 Sensor

[johnydeath]

I have a P0143 error code which I believe points to the post cat lambda sensor - I've replaced this with a tested warrantied second hand sensor, reset the engine management light but it comes back on after the usual 50 or so miles.

 The pre-cat sensor seems to have been replaced with a universal sensor spliced onto the original plug.

There do not appear to be any exhaust leaks, the exhaust is pretty good condition but has the standard rattle in the back box. The engine runs fine.

Does anyone have any tips/checks/advice please?

I'm guessing I need to diagnose voltages next, what would I look for?

 

 

[johnydeath]

Just to add to this, it flew through the MoT, readings were very good so definitely not an emissions problem:

Fast idle

CO level - 0%

HC level - 8ppm

Lambda - 1.01

Natural idle

CO level 0.08%