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Failed MOT emissions - 1.6 16V BCB engine


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#1 Ady2018

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Posted 25 September 2020 - 03:18 PM

Hi all

 

Please may I pick your brains to see if you have any ideas. My Mk4 1.6 16V with a BCB engine has just failed the MOT on engine emissions. The results from the test were,

 

Fast idle test

    CO = 1.90%

    HC = 270 ppm

    Lambda = 0,94

2nd fast idle test

    CO = 2.67%

    HC = 377 ppm

    Lambda = 0.91

Natural idle test

   CO = 0.3%

 

The engine light has been a pain for a while along with the 'workshop emissions' message so I took it to get the fault codes read and they came back as,

17588 - P1180

17591 - P1183

17604 - P1196

These suggest a fault with the wiring going to the first oxygen sensor and so I have thoroughly checked all the wiring and it is all ok with the correct voltage measurements in the wires according to Autodata,

 

Component connected

orange/brown - earth = 3.8V

orange/green - earth = 4.25V

 

Component disconnected

Pin 2 - earth = 13V

Pin 1 - Pin 2 resistance = 3 ohms

 

I am stuck, any ideas?

 

BTW: I was getting frustrated with the MOT tester who just kept saying the car needed to be scrapped due to its age. I have already had the car for 5 years and would like to keep if for another 5 as it runs great with the exception of the emissions for the MOT.

 

Many thanks

 

 




#2 ttg4l

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Posted 25 September 2020 - 07:25 PM

Could be an internal short in the sensor, try a new one. The car will run rich with a bad pre-cat O2 sensor, making it fail emissions.

I got a second hand one for under £20 and it's worked perfectly since fitting.

#3 Ady2018

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Posted 26 September 2020 - 10:32 AM

Thanks, will try swapping the sensor. I always thought that O2 sensors very rarely go wrong but according to the local motor factors it is something they always keep in stock. I don't fancy paying £120 though so will try second hand. Did you get yours from ebay?



#4 ttg4l

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Posted 26 September 2020 - 04:27 PM

Yup just put the part number into eBay.

#5 adam-

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Posted 26 September 2020 - 08:01 PM

Lamda is your clue - it's at 0.92.  The only thing that really drives warm lambda is coolant temp.  Verify it with VCDS.  Also check trims and check req. vs actual lambda.

 

Do not parts cannon.


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#6 Ady2018

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Posted 26 September 2020 - 08:20 PM

Thanks Adam. I did pay the local independent VW garage to scan the car for fault codes with VCDS and the only fault codes that showed up are,

17588 - P1180

17591 - P1183

17604 - P1196

All these indicate a problem with the wiring to the lambda sensor.

 

If there was a problem with the coolant temp wouldn't that show up as a fault code too?

 

The garage charged my £40 to scan the car for fault codes and it literally took 2-3mins so I would rather not ask them to do any more diagnostics. I could just put a engine temp sensor in for the sake of it if you think it would be worth it, surely it has to be cheaper than paying another £40.



#7 Ady2018

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Posted 26 September 2020 - 08:29 PM

I did take the lambda sensor out to see if it could be cleaned and was surprised as it was completely covered in a white coating.

 

According to the Lambda section on the Hella.com site, it can mean it is burning oil.

 

What do you think, is this normal or not?



#8 ttg4l

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Posted 26 September 2020 - 10:12 PM

The garage charged my £40 to scan the car for fault codes and it literally took 2-3mins so I would rather not ask them to do any more diagnostics. I could just put a engine temp sensor in for the sake of it if you think it would be worth it, surely it has to be cheaper than paying another £40.


Did they by any chance call it a diagnosis? Because I hate garages who call a fault code scan a diagnosis.

But anyway, wouldn't bother just putting in a coolant temp sensor without verifying the old one is bad. You can get a KKL cable off eBay for under a tenner which can read your fault codes, and view live data. Use this with VCDS/Vagcom and you'll be able to see the coolant temp reading that's sent to the ECU and you can see if it matches the gauge on the dash. Only thing to note is the dash isn't that accurate and has a bias towards 90 degrees, but it should give you a good idea as to whether the old one is bad.

#9 adam-

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Posted 27 September 2020 - 10:00 AM

If you were closer to Glasgow I'd have said come round.  I do diagnostics for good chat or a few beers.  Stuff like this isn't hard but garages are still hugely incompetent at it.


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#10 Ady2018

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Posted 27 September 2020 - 12:10 PM

Thanks all. At the end of last week, somebody advised me to buy a ELM327 lead so I can use it on the Mrs's car as well. I am still waiting for it to arrive but I assume I can get the same data from it as the KKL cable?

 

I am really keen to learn this stuff anyway. I have been tinkering with old cars since the 90's and life was so much easier then. One of my first cars was a VW Derby. If I remember right, we just had to get the CO emissions down to about 3.5% to pass the MOT and even then it was a quick adjustment with a screwdriver. What I would give to be able to walk in a car shop again and see neatly stacked boxes of distributor caps, points and rotor arms.

 

These days we have to fight with an on-board computer to fix the car instead of using old fashioned logic.



#11 ttg4l

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Posted 27 September 2020 - 03:34 PM

I have a Bluetooth elm327 and it doesn't give me anywhere near the same amount of info as my KKL lead does. The elm is perfectly adequate just for reading basic engine codes though.

#12 adam-

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Posted 27 September 2020 - 07:03 PM

It's not too bad, just a different way of thinking.  The process is the same though, you just have to understand the data and figure out what's wrong.  Everyone complains about how computers are too complicated, but the reliability is much better.  And with the feedback/data they provide, it's very easy to diagnose and determine that's wrong.

 

For example, people are quick to say your ABS light is on because of a sensor, but it could be the ring.  Use data to graph/prove which one it is, and save yourself hassle/time/money.


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#13 Ady2018

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Posted 27 September 2020 - 07:56 PM

Thanks. Although it is a pain trying to get the car through the MOT, it is proving to be a great opportunity to catch up the new technology.

 

I was going to buy a cheap and basic fault code reader but somebody said you need something which can read live data which is why they pointed me at the ELM327. I can try and buy a KKL if you think that would be better?

 

Looking at my own emissions results, the emissions got a lot worse on the 2nd fast idle test when the engine was hotter and the fan had kicked in which makes me also suspect the temperature sensor is having a hand in this as well. To be honest, I was not happy that the MOT tester left the car running for the entire time of the MOT test and then tested the emissions right at the end of the test.

 

From what I understand now, the A/F ratio is calculated by the car from inputs from,

- Lambda sensor

- MAP sensor

- Coolant temperature sensor

Is there anything else that are inputs into the calculations?

 

I once owned a Fiesta where an input to the idle speed was the pressure in the power steering pump! Unnecessary complication in my book.



#14 adam-

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Posted 28 September 2020 - 09:06 AM

It'll target lambda 1.0 unless EGT is high or coolant temp is high.  It's also dependant on the ECU calibration, as some can target richer mixtures with throttle pedal inputs, etc.  

 

It's standard practise to do emissions at the end - not all cars are warm when they come in so they leave them running to ensure the car goes into "closed loop" to make sure it targets lambda 1.0.


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#15 Mmalkie

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Posted 28 September 2020 - 05:34 PM

It'll target lambda 1.0 unless EGT is high or coolant temp is high.  It's also dependant on the ECU calibration, as some can target richer mixtures with throttle pedal inputs, etc.  

 

It's standard practise to do emissions at the end - not all cars are warm when they come in so they leave them running to ensure the car goes into "closed loop" to make sure it targets lambda 1.0.

Best advice I've ever had from an MOT Tester - Give it an 'Italian tune up' before you come in for the MOT.

(i.e. book a time slot with the garage, take the car out BEFORE the MOT (Say 30-40 mins) & give it a good 'run' at motorway speeds for 20 - 30 mins, so it is fully up to temperature)

Yes it costs you time & fuel, but I haven't failed an MOT in the last 3 years with x4 different vehicles, which includes my 1985 C reg VW Camper van.

...& yes I'm aware if you have a faulty sensor / duff wiring that won't cure it, but having the car at temperature helps with the figures.


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#16 adam-

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Posted 28 September 2020 - 05:45 PM

You have codes for a failed lamda B1S1 heater circuit.  I'd be replacing this first off.  2nd lambda also appears to be dead.  This monitors cat efficiency. 


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#17 Ady2018

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Posted 28 September 2020 - 06:59 PM

Thanks, I understand it now what the ECU is trying to do. It is adjusting the A/F map according to the engine temperature - a bit like pulling the choke out on the old cars. But, if the O2 sensor is dead then it is sending it around in circles trying to adjust the A/F ratio to a false target.

 

My last MOT guy used to insist that he did the emissions first and would always tell me to give the cars a good hot run before bringing them in.

 

I have already done the Italian tune-up with it. Well more like a faulty towers tune-up by way of a right good thrashing but down the by-pass. I will try thrashing it with a tree next!

 

I have already ordered a new pre-cat lambda sensor and was going to poor some of that 'cataclean' stuff in the tank to see if I can bring the 2nd lambda and even the CAT back to life. People seem to rave about the 'cataclean' stuff so it has to be worth a try for £10, what do you think?



#18 adam-

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Posted 28 September 2020 - 07:07 PM

Just make sure you buy an OE sensor - Bosch.  Aftermarket cheapos aren't great.  There's literally thousands of maps that lead into the calibration of final lambda.  If you want a long read, the OEM Bosch docu is available for ME7.5 (the 1.8t ECU) and describes how every single map works and how to calibrate it.  It'll draw you in.


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#19 Ady2018

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Posted 02 October 2020 - 10:17 AM

New O2 sensor has just arrived and just been fitted. Was expecting the engine light to go off straight away but it is still there and am still getting the message "Workshop Emissions". It was a genuine NGK O2 sensor. I am at a loss now as I have already checked all the wiring.



#20 ttg4l

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Posted 02 October 2020 - 11:27 AM

It usually takes 3 restarts with a rectified fault for it to turn off on its own, or alternatively clear the codes with a scanner.

#21 Ady2018

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Posted 02 October 2020 - 04:50 PM

Yes, just figured it. I tried a number of restarts earlier but worked out that you have to wait a while such as 30 mins between the restarts. The engine light has now gone off.



#22 Ady2018

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Posted 02 October 2020 - 04:56 PM

Some good news guys. Just took the car back for its MOT retest and it has passed! it actually sailed through the emissions.

 

Old values:

CO - 2.67 %

HC - 377 ppm

Lambda - 0.91

 

New values:

CO - 0.01 %

HC - 44 ppm

Lambda - 1

 

At idle the CO is now 0.00 %

 

I cannot thank all you guys enough for all the help you have given me. Another Mk4 Golf has escaped the crusher.



#23 ttg4l

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Posted 02 October 2020 - 06:37 PM

Great result.

#24 Ady2018

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Posted 03 October 2020 - 05:47 PM

I have actually got another quick question for some of you familiar with MOT testing.

 

When my car was first tested the print-out defines the CO emissions limits as 0.3 at fast idle and 0.5 at idle.

The print out I was given when the car was retested the print-out defines the CO emissions limits as 0.2 at fast idle and 0.3 at idle.

 

It has got my registration number on both emissions machines printouts and now I am paranoid that the tester has somehow fiddled the retest and tried to subject the car to stricter emission limits that it really should be just to be a bit nasty. I thought this would have all been defined by the emissions machine according to my number plate.



#25 Imagewerx

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Posted 03 October 2020 - 07:58 PM

He can't 'fiddle' it as such,the figures are defined by the machine and software it runs on as to whether it's a pass or fail.Or couldn't it be that he's done you a favour? :rolleyes:



#26 Ady2018

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Posted 04 October 2020 - 01:18 AM

I have just looked and noticed on the retest slip that it has got my registration number but there is no mention of what car it is like on the original MOT test slip. I suspect that the emissions machines are not capable of working out what make and model of car it is from the registration number.

 

He certainly hasn't done me a favour as he bought the maximum limit down from 0.3 to 0.2 which increased the probability of failing the MOT retest which is what I am upset about. There must be a database somewhere where us public can look up what values should really be used for our MOT tests.







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