1.6 BCB p0138 and p0171

[lukeharper777]

So.. ive got a mk1 leon with the 1.6 bcb engine and i keep getting the code p0171 and p0138

So far i have replaced..
Cat
Both 02 sensors
Map sensor
Injectors and fuel rail
Spark Plugs

car originally went in for an mot and failed on emissions, so i replaced the manifold and the second cat with both the 02 sensors and it flew through the mot

about 2 weeks post mot the car started running rough and we got the code p0171 and have since replaced the parts above (including a new secondary cat because it was blocked)

the car is at a point now where it runs smoothly, drives nice and so far the p0171 code doesnt seem to be coming on

but code p0138 is intermittent, could this just be another faulty 02 sensor?

im really at a loss at this point and am failing to think of any solutions so any help would really be appreciated

 

[mty12345]

Was it a branded O2 sensor (like bosch) or some no name amazon type stuff? If it was a cheap sensor they can give dodgy outputs that upset the ECU. Either way, the second O2 sensor doesn't do anything other than monitor the cat, so won't be causing any issues.

If the p0171 code comes back, i'd be looking for a split pipe in your PCV system. 90% of lean codes are usually vacuum leak related. The car sucks in some air that hasn't been through the MAF, so ECU sees that as the mixture being lean. If you have a OBD2 reader you can look at your long and short term fuel trims (LTFT) (STFT) for a better idea of the issue.