ryanw2427

Does anyone know if a disconnected PCV fresh air intake duct would cause the check engine light to come on intermittently and throw the P0171 code for "system too lean?" This has been disconnected for a while, I'm guessing from where we had our oil changed last since they also changed the air filter. It's only been a couple days since I found and reconnected it, but I was interested to hear a technical explanation.

Thanks.

92civlude

Yes. It happens all the time! It sets a lean DTC because the PCM only knows about the air going through the MAF sensor. The air going through that nipple is additional air. the Air fuel sensor sees this as a lean condition and tries to richen the system by lengthening the injector pulse. It gets to the point the system is adjusting the system beyond programmed parameters. The pcm reckognizes this as a problem and sets a code.

brian67

Thanks for the explanation.I am new here and was also in search of this explanation.Its good to know.

ryanw2427

Thanks a lot for the response! That is very helpful.

soon2bdropped

wow. dude right on the money.