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Matt, Mechanical Engineer
Category: Car
Satisfied Customers: 22727
Experience:  BEng hons Mech engineering, in auto industry 22 years
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Toxic fume light staying on after car startup. Renault

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toxic fume light staying on after car startup. Renault megane scenic
1398cc 2003. new valves fitted following timing belt all associated repair/refit /reassemble work. Fault codes not found
after Snap on test equip. employed.


if you have the exhaust emissions light on then this means there's an issue with the post cat O2 sensor or the catalyst itself

Its quite possible that the cat has been damaged by the previous engine damage

If the car feels down on power then this would back this up as a damaged cat can collapse and block the exhaust

so I'd suggest to remove the O2 sensor thats closest to the engine and see if you can peer inside the exhaust to view the cat brick as it should be nice and even

if that looks OK then I'd say to consider replacing the second O2 sensor ( the 1 after the cat further down the exhuast)

and also consider using a bottle of this

as its good for cleaning up the o2 sensors , fuel injectors as well as the cat

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