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[Kevin Wood]

.. actually, I think the cat is relinquishing oxygen into the exhaust when it breaks down CO and NOx from the exhaust gases so that's probably why it reads lean, and would start blipping up to rich in unison with the front sensor if the cat were not working.

Kevin

[Kevin Wood]

Wikipedia says (rather vaguely):

The second sort of diagnostic is more complex and is a result of the California OBD-II rule (though temperature sensors are sometimes used for this). In vehicles with OBD-II, a second oxygen sensor is fitted after the catalytic converter to monitor the O2 levels. The on-board computer makes comparisons to the readings of the two sensors. If both sensors give the same output, the catalytic converter is non-functioning, and must be replaced. It will also spot less serious damage to a catalytic converter, such as the use of racing fuel in an on-road vehicle. Lead is still legal in racing fuel, and use of as little as half a tank of leaded fuel will cause enough damage for the computer to notice, and warn the operator that the converter is not functioning properly.

[Dave-C]

Blocked air filter??

[MikeDundee]

Ok folks thanks for all the feedback so far, great stuff ...so on saturday I am going to be cleaning out the breathers (nothing to do with this problem), and checking for air leaks, and looking at the MAF meter (even though not sure what I am looking for when checking).

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

Please forgive me folks as I am by no means a mechanic, but will atempt minor jobs.  

[Kevin Wood]

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

I wouldn't say you have a cat problem, TBH. Did the fault codes recurr after they were cleared?

I think the cycling of the front sensors proves they are working to some degree. The rear sensors are reading constant lean which I think is OK and means the cats are working. The problem is that the front lambda sensors have caused too great a fuelling correction and put the fault light on. This could be due to two failed lambda sensors but I'd say this is unlikely. More likely is that something else is feeding the ECU with duff information which is causing it to correct more than it should, or something has contaminated the lambda sensors.

Check for anything likely to cause an air leak while you're doing the breathers. It might be worth putting a tankful of decent fuel through it, and trying some injector cleaner just in case the fuel system is not delivering fuel as it should. I guess air filter is a possibility although the MAF should have been reading the correct airflow even if this was restrictive. It's worth giving the throttle body a clean while you're at it.

Has the fuel filter been changed recently?

Kevin

[Taxi_Driver]

Ok folks thanks for all the feedback so far, great stuff ...so on saturday I am going to be cleaning out the breathers (nothing to do with this problem), and checking for air leaks, and looking at the MAF meter (even though not sure what I am looking for when checking).

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

Please forgive me folks as I am by no means a mechanic, but will atempt minor jobs.  

Dont think you will have an air leak.....as ECU would be recording a MAF sensor fault.....when you find the MAF sensor.....dont go prodding it....they are fairly delicate.....just inspect visually for dirt on it....if it is dirty....they can be cleaned.....i think i read somewhere as gently swirling about in a container of white spirit does the trick......BUT wait till someone else advises how to clean it......i tend to melt things when i try cleaning   Altho my expansion bottle seems to have survived the abuse i gave it  

[TheBoy]

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

I wouldn't say you have a cat problem, TBH. Did the fault codes recurr after they were cleared?

I think the cycling of the front sensors proves they are working to some degree. The rear sensors are reading constant lean which I think is OK and means the cats are working. The problem is that the front lambda sensors have caused too great a fuelling correction and put the fault light on. This could be due to two failed lambda sensors but I'd say this is unlikely. More likely is that something else is feeding the ECU with duff information which is causing it to correct more than it should, or something has contaminated the lambda sensors.

Check for anything likely to cause an air leak while you're doing the breathers. It might be worth putting a tankful of decent fuel through it, and trying some injector cleaner just in case the fuel system is not delivering fuel as it should. I guess air filter is a possibility although the MAF should have been reading the correct airflow even if this was restrictive. It's worth giving the throttle body a clean while you're at it.

Has the fuel filter been changed recently?

Kevin

I cleared the codes, and we went for a little drive whilst I did a live data. pre-cat sensors looked fine, wasn't sure about post-cat (as I wasn't sure what they should read). Everything else looked fine. EML stayed off. A couple of hours later, he called me to say the EML had popped on again

[MikeDundee]

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

I wouldn't say you have a cat problem, TBH. Did the fault codes recurr after they were cleared?

I think the cycling of the front sensors proves they are working to some degree. The rear sensors are reading constant lean which I think is OK and means the cats are working. The problem is that the front lambda sensors have caused too great a fuelling correction and put the fault light on. This could be due to two failed lambda sensors but I'd say this is unlikely. More likely is that something else is feeding the ECU with duff information which is causing it to correct more than it should, or something has contaminated the lambda sensors.

Check for anything likely to cause an air leak while you're doing the breathers. It might be worth putting a tankful of decent fuel through it, and trying some injector cleaner just in case the fuel system is not delivering fuel as it should. I guess air filter is a possibility although the MAF should have been reading the correct airflow even if this was restrictive. It's worth giving the throttle body a clean while you're at it.

Has the fuel filter been changed recently?

Kevin

No the fuel filter has'nt been changed since I boUght it in Nov 2003, I always use BP stuff apart from the other eek wehn I topped it up with Morisson fuel. I put Wynns injector cleaner in before I went up to see TB  on Tuesday. Throttle body, book of lies recommends new seals, so may have to leave that if I can't get the seals, But I would have assumed when the seals where all done in April the y would have had to remove the throttle body and replace the seals in any case, even though they may have not cleaned the throttle body.  

[TheBoy]

So the way I see it so far Lambda's are Ok, o2 sensors are OK, May have a problem with the CAT?

I wouldn't say you have a cat problem, TBH. Did the fault codes recurr after they were cleared?

I think the cycling of the front sensors proves they are working to some degree. The rear sensors are reading constant lean which I think is OK and means the cats are working. The problem is that the front lambda sensors have caused too great a fuelling correction and put the fault light on. This could be due to two failed lambda sensors but I'd say this is unlikely. More likely is that something else is feeding the ECU with duff information which is causing it to correct more than it should, or something has contaminated the lambda sensors.

Check for anything likely to cause an air leak while you're doing the breathers. It might be worth putting a tankful of decent fuel through it, and trying some injector cleaner just in case the fuel system is not delivering fuel as it should. I guess air filter is a possibility although the MAF should have been reading the correct airflow even if this was restrictive. It's worth giving the throttle body a clean while you're at it.

Has the fuel filter been changed recently?

Kevin

No the fuel filter has'nt been changed since I boUght it in Nov 2003, I always use BP stuff apart from the other eek wehn I topped it up with Morisson fuel. I put Wynns injector cleaner in before I went up to see TB  on Tuesday. Throttle body, book of lies recommends new seals, so may have to leave that if I can't get the seals, But I would have assumed when the seals where all done in April the y would have had to remove the throttle body and replace the seals in any case, even though they may have not cleaned the throttle body.  

Change the fuel filter - its about £5 or £6 on TC, but remember the 2 little clips as well (50p each)

[Kevin Wood]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

[MikeDundee]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

Before I left Biling, I topped up the oil, and after I left was on the dual carriageway, some idiot in front hit his brakes cos someone in front of him, I obviously had to do the same thats when the light came on, reckon its taking about a litre plus per 1,300 miles. However, before i got to TB's work on Tuesday Oil check came on then never showed again till just before oxford, seems to come on and off at times. :-/  

[TheBoy]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

Before I left Biling, I topped up the oil, and after I left was on the dual carriageway, some idiot in front hit his brakes cos someone in front of him, I obviously had to do the same thats when the light came on, reckon its taking about a litre plus per 1,300 miles. However, before i got to TB's work on Tuesday Oil check came on then never showed again till just before oxford, seems to come on and off at times. :-/  

Are you also checking oil on dipstick?

[MikeDundee]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

Before I left Biling, I topped up the oil, and after I left was on the dual carriageway, some idiot in front hit his brakes cos someone in front of him, I obviously had to do the same thats when the light came on, reckon its taking about a litre plus per 1,300 miles. However, before i got to TB's work on Tuesday Oil check came on then never showed again till just before oxford, seems to come on and off at times. :-/  

Are you also checking oil on dipstick?

Yes have been, just checked the dipstick, oil up to the first notch, which means I need to put around 1 litre back in. What i can't get my head round is that there always oil on the last notch, but nothing on the notches in between, have to assume this is normal

[TheBoy]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

Before I left Biling, I topped up the oil, and after I left was on the dual carriageway, some idiot in front hit his brakes cos someone in front of him, I obviously had to do the same thats when the light came on, reckon its taking about a litre plus per 1,300 miles. However, before i got to TB's work on Tuesday Oil check came on then never showed again till just before oxford, seems to come on and off at times. :-/  

Are you also checking oil on dipstick?

Yes have been, just checked the dipstick, oil up to the first notch, which means I need to put around 4 litres in. What i can't get my head round is that there always oil on the last notch, but nothing on the notches in between, have to assume this is normal

Eh? there are 2 marks on v6 one - min and max. Difference between min and max is 1l

[MikeDundee]

Throttle body is a long shot anyway, TBH. Any air that goes through it is metered so even if it's dirty it probably wouldn't contribute to the problem.

Can you remember what you were doing when the light came on again?

How much oil is it losing at the moment? I wonder if oil consumption is affecting the lambda sensor readings  :-/

Kevin

Before I left Biling, I topped up the oil, and after I left was on the dual carriageway, some idiot in front hit his brakes cos someone in front of him, I obviously had to do the same thats when the light came on, reckon its taking about a litre plus per 1,300 miles. However, before i got to TB's work on Tuesday Oil check came on then never showed again till just before oxford, seems to come on and off at times. :-/  

Are you also checking oil on dipstick?

Yes have been, just checked the dipstick, oil up to the first notch, which means I need to put around 4 litres in. What i can't get my head round is that there always oil on the last notch, but nothing on the notches in between, have to assume this is normal

Eh? there are 2 marks on v6 one - min and max. Difference between min and max is 1l

  yeah fair enough,   was counting the notches on the dipstick, which there are 4 of , potentially may have been topping it up too much?, been looking for one of those oil jug thingy's but can't seem to find one, to avoid over filling ....could that contribute to the Tech 2 readings?