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P0172 Engine Code

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rossh123

Original Poster:

3 posts

2 months

Tuesday 26th September
quotequote all
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 smile

GreenV8S

24,745 posts

206 months

Tuesday 26th September
quotequote all
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

Original Poster:

3 posts

2 months

Tuesday 26th September
quotequote all
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. confused

Edited by rossh123 on Tuesday 26th September 20:27

Mr2Mike

17,669 posts

177 months

Thursday 28th September
quotequote all
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 smile
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

373 posts

11 months

Thursday 28th September
quotequote all
Check your exhaust manifold they are prone to hairline cracks
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