Codes P0171 And P0174

[johntom]

Hi

I have a 2001 2.0 vvti and I get the EML and above codes when driving up hill under load ie higher gears and at speed. What are the most likely causes on a rav4, air leaks, blocked filters etc and where do I start?

[gjnorthall]

It's good when the two codes come up together - it sort of cross confirms over both banks that the fuel mixture is weak to the extent that the Lambdas cannot correct. In 80% of cases it's due to a dirty filament on the airflow meter so that it under-reads the airflow and therefore sets too low a fuel flow. In the first instance - clean the filament of the MAF - this has been covered elsewhere on this forum and should be done with care. The air-filter protects the MAF so change it if there's any issue about it's condition.

[johntom]

Hi thanks for that, I have it removed and have just carefully wiped off a covering of black oily dirt from the filament with a cotton bud. Can't find the contact/switch cleaner so I will leave as is and retry the car.

[johntom]

Hi

I cleaned the maf and the EML has stayed off for a few hundred miles. Then tonight the EML has returned, this time the codes are p0420 and p0430 relating to cat efficiency ? Could this still be the maf, I only wiped it with a cotton bud last time?

[gjnorthall]

You often find P0420 and 0430 together and basically it means that the catalytic converter isn't performing as it should. This could mean that the cat is shot, but hopefully, in this case, and given the previous symptoms - it's because the cat is being fed with a sub - optimum mixture as a result of incorrect airflow rate. The MAF needs to be cleaned properly using a proprietary MAF filament cleaner or electrical contact cleaner - don't touch the filament. Sometimes it's just not possible to clean off baked on oily deposits - but it's worth trying before replacing the MAF. As previously noted - change the air filter if there is any doubt about it's condition.