MOT failure - emissions...

[Bongo]

My car has just failed it's MOT, apparently on fast idle emissions.

Technician has had a look and reckons it's because the precats aren't there and bank 1 o2 sensor is reading too high.

On a side note they told me that it's quite common for the precats to die, but there's usually some there so they wondering whether they were removed...

No it's not the unichip as that's not on there.

Any ideas on what could be wrong, bar doing a general ECU reset and clean the MAF etc?

[markiii]

was your car warm when they did the emissions check?

you need teh prercats to pass from cold, but if it's hot you should be fine

[Bongo]

Good point, i can't imagine they'll have warmed it up first, especially if it's meant to pass when it's cold.

I will double check with them.

[Stifler]

Crud, my car is getting its MOT this saturday (sans precats) - is it common that they fail the emissions test  s:shock: :shock: s:shock:   - now im a bit worried....

[markiii]

make sure you turn up in teh car for teh time booked so it's still warm rather than leaving it wait all day until they are ready

[SteveJ]

Cars in the UK do NOT require pre-cats, and hence should only be tested once the vehicle is warm.

There is a prescribed minimum run time prior to the test being performed, and this should be plenty of time for our main cat to reach operating temp given the short exhaust length compared to most front engined cars.

The pre-cats are a requirement to pass Californian emissions laws

[Stifler]

ok, thanks for that, i'll give her a good beasting on the way to the test center   s:twisted: :twisted: s:twisted:

[Bongo]

Stats:

Fast Idle test:

CO: 0.48% Vol - fail, (<= .30% pass)
HC: 17ppm vol (<= 200ppm pass)
Lambda .990 (pass range: 0970-1.030)

Second fast idle test
CO: 0.47%
HC: 7ppm
Lambda: .990

Diagnosis, no precats (obviously), faulty O2 sensor?

I had no CEL so i don't know whether they've borked the O2 taking a look at precats or what...

they say the car was warm as the machine won't let them procede if it isn't at the right temp.

[Anonymous]

Stats:

Fast Idle test:

CO: 0.48% Vol - fail, (<= .30% pass)
HC: 17ppm vol (<= 200ppm pass)
Lambda .990 (pass range: 0970-1.030)

Second fast idle test
CO: 0.47%
HC: 7ppm
Lambda: .990

Diagnosis, no precats (obviously), faulty O2 sensor?

I had no CEL so i don't know whether they've borked the O2 taking a look at precats or what...

they say the car was warm as the machine won't let them procede if it isn't at the right temp.

Perhaps it is your main cat that is the problem then?

[GSB]

2 courses of action here for you...

1, is to change the air filter, clean the MAF, and run a bottle of injector cleaner through the tank. Then thrash it like a ginger stepchild all the way to the MOT station, and put it straight on the machine.

2, is to find a more leniant MOT tester, that CO readings not that bad, so option 1 would in liklihood be fine.

[Anonymous]

thrash it like a ginger stepchild

  s:lol: :lol: s:lol:    s:lol: :lol: s:lol:    s:lol: :lol: s:lol:

[Anonymous]

Mines just passed the emmissions test without pre-cats (engine was warm) - failed on the non-existant handbrake tho   s:oops: :oops: s:oops:  DOH

[red_leicester]

failed on the non-existant handbrake though

What's one of them ?

[Peter Laborne]

1, is to change the air filter, clean the MAF, and run a bottle of injector cleaner through the tank. Then thrash it like a ginger stepchild all the way to the MOT station, and put it straight on the machine.

This is what I would have gone for. Considering as we know the 2 can pass an MOT without the pre-cats, we know we can rule that out as being the problem.

Try going for the above and then the old unplug the battery for a while to reset the ECU.

A couple more questions:
1) Have you any engine mods, no matter how small?
2) Where fuel do you use (Optimax, Ultima, Tesco 99RON etc)?
I ask because it might help narrow down MOT failures in the future and lead to a more instant diagnosis for any future problems.

2, is to find a more leniant MOT tester, that CO readings not that bad, so option 1 would in liklihood be fine.

But with the new computer based MOT tests wouldn't that make this impossible now?

[Peter Laborne]

2) Where fuel do you use

I could have just edited that bit....but:
ALL YOUR BASE ARE BELONG TO US   s:lol: :lol: s:lol:

[Bongo]

2 courses of action here for you...

1, is to change the air filter, clean the MAF, and run a bottle of injector cleaner through the tank. Then thrash it like a ginger stepchild all the way to the MOT station, and put it straight on the machine.

2, is to find a more leniant MOT tester, that CO readings not that bad, so option 1 would in liklihood be fine.

I was planning on a bit of both...

A couple more questions:
1) Have you any engine mods, no matter how small?
2) Where fuel do you use (Optimax, Ultima, Tesco 99RON etc)?

1) Markiii pipe (also noticed by the dealer...), TRD filter, H&S exhaust.

2) I usually fill up at shell mostly on regular with the occasional optimax.

A further look at the paperwork reveals the test was carried out at 11am, so the car had been sat around for 2 hours. Oil temp was 60 degrees C which is the minimum allowed for the test.

I believe the TRD filter is cleanable and reusable? How would I do this?

MAF and ecu reset is easy enough, will a nice thrash to the test centre be enough for it to have "learnt", will a longer drive be necessary or will it be ok even if freshly reset?

[Anonymous]

Lambda sensors become weaker/slower over time. Try swapping the Lamda sensors over to see if the high reading moves with the sensor, if it does you know what the problem is.

Alternatively, borrow some sensors off someone elses car for the test and see if that works.

My old Scorpio went in 8 times before she passed

[markiii]

check for exhaust leaks

Liz's failed due to a leaky joint between her cat and H&S apparently it sucks in air and screws up the readings

[philster_d]

If you have a free retest just go for a long drive then drop in for it "while you wait" it will surely be red hot then.

[Tem]

Cat converts CO to CO2, so I bet it's the cat. If the car was at normal temp, it would mean a dying cat, but if it was cold, it just means the cat wasn't operating yet.

Lambda sensors become weaker/slower over time.

I don't think that's it, cause his lambda values are just fine.

check for exhaust leaks

That should show as high O2 reading, not CO.


I'm with the most, just retake the test when it's warm.  s8) s8)

[Bongo]

Thanks for all the advice so far...

I'll post any updates here.

The natural Idle result was fine - a pass!

[Anonymous]

But with the new computer based MOT tests wouldn't that make this impossible now?

Apparently there are still places where as long as the car turns up you can gaurantee a pass.

I also believe you have to rebook for a retest now and they carry out a full MOT not just the fail parts.

[Anonymous]

But with the new computer based MOT tests wouldn't that make this impossible now?

Apparently there are still places where as long as the car turns up you can gaurantee a pass.

I also believe you have to rebook for a retest now and they carry out a full MOT not just the fail parts.

I went to my MOT station today - once I had sorted out the dodgy handbrake !! The chap checked the handbrake which was fine and then booked me in for a full retest on Monday at £22. He told me that the rules are changing soon and cars will be retested on only those parts that failed the original test and anything associated with that part of the fail. So things should get easier.  s:wink: :wink: s:wink:

[Stifler]

Mine past yesterday with flying colours (with out the pre cats) £45 tho, ooft  s:( s:(

[philster_d]

Hmm my tubby failed last year on 2 things and I only had to go back the next day to confirm they were done. Not a full retest.

Phil