P0172 Engine Code

[rossh123]

Hi All,

I have a 1999 Yaris which has recently had the check engine light come on with code P0172 - System Too Rich.

I've tried using super unleaded fuel, also tried cleaning the MAF sensor which helped make the acceleration smoother but the check engine light came back 3 days later.

Every time I reset the light, it comes back within 3 days and it only comes back on when the car is idling.

The MOT emissions report shows that the CO is just under the pass limit.

So i'm thinking it's either an oxygen sensor or the cat. Any thoughts?

Thanks,
Ross

[GreenV8S]

rossh123 said:

tried cleaning the MAF sensor

Is it a hotwire sensor? Their sensing elements are fantastically sensitive to contamination and I imagine would be very tricky to DIY clean.

[rossh123]

GreenV8S said:

Is it a hotwire sensor? Their sensing elements are fantastically sensitive to contamination and I imagine would be very tricky to DIY clean.

I think it is, but considering i've got an increase in performance since cleaning it and the light still comes on, i'm thinking the problem lies elsewhere.

Edited by rossh123 on Tuesday 26th September 20:27

[Mr2Mike]

rossh123 said:

Hi All,

I have a 1999 Yaris which has recently had the check engine light come on with code P0172 - System Too Rich.

I've tried using super unleaded fuel, also tried cleaning the MAF sensor which helped make the acceleration smoother but the check engine light came back 3 days later.

Every time I reset the light, it comes back within 3 days and it only comes back on when the car is idling.

The MOT emissions report shows that the CO is just under the pass limit.

So i'm thinking it's either an oxygen sensor or the cat. Any thoughts?

Thanks,
Ross

It won't be the cat, that affects tailpipe emissions not how rich or lean the engine is running. Dead/dying MAF is a common cause of this, but also could be caused by an induction or exhaust air leak or duff oxygen sensor.

[Bdevo3]

Check your exhaust manifold they are prone to hairline cracks