Engine Fault

[richard.c]

Hi All,

Know its a 'How long is a piece of string' question, but hope someone can suggest some diy answers .

My 1999 Avensis, 1.8 petrol lean burn, 7AFE type has done 136,000 miles and still averages me 40+ mpg, and all parts are still the original.

For about the last 9 months, the engine check light comes on for a few minutes, usually when driving in slowish traffic ( low revs ), on average once or twice a week.

Reading the code out as 21, oxygen sensor, but I have swapped it with another known good one and still get the same error.

I had the car MOT tested the other month and it passed the Emmision test , but literally on the line

Fast Idle Test CO level 0.15 % Limit 0.20 %

HC level 29 200

Lambda 0.999 1.030

Natural Idle Test 0.30 % Limit 0.30 %

Despite a diy full B service last month, new Irridum plugs at 120K, two bottles of injector cleaner, checking for loose/split hoses etc I am now at a dead end as to what to do.

With its age on mileage, although it otherwise is good nick, its really not worth spending a mountain of cash on it in Mr Ts diagnostic bay.

thanks

Richard

[cmia]

I have seen this before,

its a problem with the lean burn system its self!

search, iam sure it has been covered it before

[richard.c]

I have seen this before,

its a problem with the lean burn system its self!

search, iam sure it has been covered it before

Hi Cmia,

Did search before and since your reply but unable to find anything similar .. ?

I only have the Hayes manuals and virtually nothing on the lean burn system, all I can establish is that its a small air control valve under the inlet manifold - I don't know what controls it - no hint of a sensor other than the oxygen sensor, which as I say gives the same fault when replaced.

Can you give me any other clues,

thanks.

[Danny K]

If it still is a faulty sensor then eventually the red engine light will come on - and stay on permanently. Then you know for definite - it's the sensor.

I get confused with all the sensors - all I know is in the last Toyota lean burn engine car I owned, the dealer charged me £300+ to replace and fit, (might have been some other jobs on that bill too) stating that the 'oxygen sensor' is part of the exhaust system. That was enough to put me off investigating further and I paid them to do it for me. Years later when I came to sell that car at 140K mileage the red engine light symbol had recently come back on - permanently. The buyer brought a cheap secondhand sensor from a Vauxhall and fitted it in 20 seconds or so - and the red light went out. I always thought there were two as the same garage advised me this time that the part that needed replacing was 'in the engine'. But was it the same sensor replaced twice over? If so I was astonished how easy it was to fit when watching the new owner fit it before driving away. Literally seconds, was all it took.

By the way, 136k is nowt to a lean burn engine - as you testify, you still get over 40mpg out of it. However the poor emissions record print-out leads me to believe you've still got a problem with the sensor, as it is part of the exhaust system.

So if it is the oxygen sensor that's playing up, can you be sure the one you fitted was in perfect health? Because if it was accidentally dropped before being handed over to you, or ANY cleaning materials were used on it, then it's highly likely to be damaged. In other words - it's very, very, delicate, as in: handle with care.

Then again if it was totally Kaput, the engine light would be on all the time and not just occasionally.

- Incidentally, on a pedantic point, everyone calls it the oxygen sensor - but that's only for conventional engines. The sensor in the lean burn engine is called a lean mixture sensor, (same thing really). However, even the Toyota mechanics refer to it as the oxygen sensor, as does the read-out code thing.

[richard.c]

However the poor emissions record print-out leads me to believe you've still got a problem with the sensor, as it is part of the exhaust system.

So if it is the oxygen sensor that's playing up, can you be sure the one you fitted was in perfect health? Because if it was accidentally dropped before being handed over to you, or ANY cleaning materials were used on it, then it's highly likely to be damaged. In other words - it's very, very, delicate, as in: handle with care.

Then again if it was totally Kaput, the engine light would be on all the time and not just occasionally.

- Incidentally, on a pedantic point, everyone calls it the oxygen sensor - but that's only for conventional engines. The sensor in the lean burn engine is called a lean mixture sensor, (same thing really). However, even the Toyota mechanics refer to it as the oxygen sensor, as does the read-out code thing.

Hi Danny,

Actually I have had two replacement sensors, first a new one, because the heater had gone open circuit on the original one, but then this brand new one gave this odd problem so I tried another old one from another Avensis still get exactly the same results.

There is one slow downhill route home that has loads of speed cameras for about 6 miles and you can guarantee the check light will come on by the end of it, yet it will generally be fine for all other routes for the rest of the week.

Think I slipped up at the mot test, he finished a bit early, should have asked if I could put the other sensor in to see how it read .

Just that as you know Mr T never happy with ' occassional ' fault readings - and with the age of the car is not worth opening a bottomless pit - not that I have got one !