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Matt, Mechanical Engineer
Category: Toyota
Satisfied Customers: 22727
Experience:  BEng hons Mech engineering, in auto industry 22 years
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i took my toyota avensis 1.8 petrol (1997)for its mot and

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i took my toyota avensis 1.8 petrol (1997)for it's mot and it failed the test,the co2 readings were too high they said to change the "cat" which i did ,and it was still too high . so they said to change the lamda sensor ,which i did and again it was still too high.then they said try an additive in the petrol tank and take it for a 50 mile run at high speed which i did and again it was still too high .then they said change the air filter,oil filter and do an oil change and also change the spark plug's.i done everything that they said and i am getting nowhere the emissions are still too high. the car runs great and iv'e had her since new and she is serviced every year this is the first time iv'e ever had a failure.i had her in the garage a few months ago to have a new battery fitted and one person said to me that if the battery is disconected for any length of time then the engine computer goes back to the original factory settings and this would cause the problems that im having. can you help me?

if the battery is disconnected then yes the ECU goes back to factory settings

however after about 20 miles or so its re-learned any changes required anyway

I'd suggest checking for a faulty water temp sensor. If this is the problem then the ECU will be leaving the car constantly ' on choke' and not reducing the fuelling as the engine warms - so unplug the sensor and clean the contacts on both sides with some switch / electrical cleaner (not WD40) and inspect the wiring for any signs of damage to the insulation especially where it runs over other components and through the bulkhead- if this doesn't help consider replacing the sensor as they're not expensive

Also check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

Customer: replied 3 years ago.

hi Matt,sorry that iv'e not repied sooner but by the time i had a chance to get to the computer to see your answer i did'nt get to order the parts untill sat. morning and hopefully i will pick them up tues. afternoon and i will take it from there (weather permitting) and as soon after i will let you know the results. Tommy.

Understood Timmy

good luck
Customer: replied 3 years ago.

hi Matt,i got the parts yesterday they are now fitted. i took the car to the garage this morning and got them to run an emissions test and again it failed after much debate between themselves they are saying it's the "cat". and as it's only 8 month's old i've contacted the supplier and now i await for them to get back to me.


I'd agree that for the cat to be faulty after such a short period of time means either its a faulty part or its been poisoned somehow by a faulty sensor

I think the latter is more likely so I'd ask about the checking the sensors I mentioned earlier and also consider a new set of a spark plugs as well
Customer: replied 3 years ago.

hi Matt,the company that i bought the exhaust from read the report from the garage and have agreed that the "cat" is faulty and as it's still under warranty and as such they are going to send another one to me tommorow and as i've replaced the water temperature sensor and the thermostat, spark plugs,air filter,oil filter, oil,lamda sensor keep your fingers crossed for me that it's all ok.



OK Tommy

good luck
Customer: replied 3 years ago.

hi Matt ,got the cat and it,s all fitted at last took it to the garage yesterday and at last every thing is good in fact the guy at the garage said that the readings are better than when it was a brand new car so thank's for all your help.


Glad to have helped Tommy

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