High CO Emissions

[hambleton1]

Hi All,

My Yaris has just gone over the CO limit on the MOT emissions test. Everything else is normal HC, Lambda etc.

The code P0172 is also showing which is "System Too Rich".

The car is 19 years old and when it's first started I can smell petrol outside and sometimes when I get out after driving it I can smell it too. I've tried Cataclean and i've also cleaned the MAF.

I'm thinking it's the CAT? Any thoughts?

Ross.

[Devon Aygo]

Toyota's diagnostics for P0172 state the possible causes as:

1. Injector blockage
2. Manifold absolute pressure sensor
3. Engine coolant temperature sensor
4. Fuel pressure
5. Gas leakage from exhaust system
6. Open or short in heated oxygen sensor (sensor 1) circuit
7. Heated oxygen sensor (sensor 1)
8. ECM

The catalyst cannot cause a "System too rich" fault something is causing the engine to over fuel 

[hambleton1]

20 minutes ago, Devon Aygo said:

Toyota's diagnostics for P0172 state the possible causes as:

1. Injector blockage
2. Manifold absolute pressure sensor
3. Engine coolant temperature sensor
4. Fuel pressure
5. Gas leakage from exhaust system
6. Open or short in heated oxygen sensor (sensor 1) circuit
7. Heated oxygen sensor (sensor 1)
8. ECM

The catalyst cannot cause a "System too rich" fault something is causing the engine to over fuel 

 

But if the cat isn't working properly and doesn't convert the CO emissions, wouldn't the post-cat oxygen sensor detect this and throw the error code.

[Devon Aygo]

Not in this case, the Pre cat sensor detects the "System too Rich" ( Hence the checks on the Pre Cat Senor 1) as the air fuel ratio is either too rich or being detected so before it even passes through the cat, if the the issue were with the cat then you would have a code for "Catalyst below efficiency" where the reading pre & post Cat show that it is not reducing the emissions as designed

[Madasafish]

Money is the Mass Air flow sensor. How did you clean it? If not with carb cleaner and great care  (possibly a cotton bud as well) then you may have not cleaned the wire properly  or even damaged it as it is very sensitive. As it is is ancient it may just be FUBAR and a replacement needed

[fordulike]

Do not use cotton buds!

www.mafcleaning.co.uk