I have clear it twice but it comes back after a couple of days, the car is 66reg, 21000 miles, anyone know if it is lambda sensor, cat, or leaking exhaust. Or any other idea

 

I doubt it's the cat after that mileage, but the O2 sensor may be faulty. On other cars, I have heard that the code can also be caused by over-filling of engine oil, a leaking fuel injector, or a faulty engine temperature sensor. For the latter you'll need Move&Fun (or VW up version) to check if water temp gets correctly reported.  There may be other root causes, but for some reason, 'the internet' likes to blame the most expensive component first! (The cat).

 

It could even be a dirty MAF, affecting fuel mixture, but there might be other codes for that.

 

Edited 29 March, 20206 yr by freemansteve
Added MAF

> "Or any other idea".

 

The fault code suggests a problem with the exhaust emissions.  This involves the lambda sensor (measures the oxygen in the exhaust), the CAT (cleans the exhaust gases).  But other problems could exist with the control side of the emissions i.e.the mass airflow sensor (measures the air going into the engine), fuel injectors, engine temperature etc.

 

All are linked using wiring and connectors, so before you replace anything, check all the wiring and connectors for corrosion.  Corrosion will increase the resistance across the connectors and can give a false readings to the Electronic Control Unit.

 

Disconnect the sensors and clean the contacts, then seal them (battery terminal spray is good) and check again. 

 

Have you had any work done prior to the fault codes being exhibited?  Re-check these areas e.g. the air filter housing may have become dislodged or not refitted correctly and is causing the engine to run lean etc. etc.

 

Good luck.