Failed mot on CO emissions tried everything stumped

MissSpentYouth · Oct 20th, 2017, 21:37

Hi All, I have a 2001 s80 2.4 20V petrol 170 BHP auto with 77K miles in brilliant condition runs perfect. Just failed its MOT on high CO about 1.5% were the pass mark is less than 0.3% so well over. Both HC and Lambda passed.

Just one curious code on Veda which relates to the upper Lamba sensor heater circuit. Sure enough the Lambda sensor heater circuit was open circuit so I replaced it but was surprised to find the same error come back again shortly afterwards. One side of the heater circuit is supplied with a 12V feed where as the other is switched to ground through the ECU, seems my ECU might be faulty as it doesn't seem to ground out the heater circuit, so as a temporary fix I have disconnected the ECU and hard wired the heater to ground. Made no difference to my CO reading I don't think the heater circuit is required once the CAT is up to temperature.

Things I have checked, plugs all good and the right colour, new air filter, smoke tested the induction system for leaks. MAP sensor readings look good and in spec as do the MAF sensor readings. Tested the PVC system with a glove over the engine filler all good showing a vacuum. Tested the purge valve no leaks. Checked the cam timing all good.

The car only gets used a few times a week and for short trips so I took it along the motorway locked in 3rd for 15 minutes to cook the CAT this improved things significantly but still a fail about 0.8% CO.

Put on a new after market CAT this made the CO worse back up to 1.5% so just fetched that off again and put the original one back. Just tried a new lower Lambda sensor in desperation and will do some more longer trips before taking back for testing on Monday.

If I disconnect the lambda sensor i.e run the car open loop then I see about 0.8V from the sensor so the car would run rich left to its own devices. If I reconnect it the value drops to 0 as I think the ECU must load it up and use it in a current sensing mode rather than voltage but I could be wrong on this one.

I am completely out of ideas on this one ? Car runs perfectly idle nice and steady no hint of a misfire, compression good, engine is mint as is the rest of the car.

wondering if I could add a small air leak downstream of the MAF to see if that would get it to run leaner, however I would have thought the Lambda sensor would pick that up and just correct for it in any case.

Simon Jones · Oct 21st, 2017, 07:19

The chaps in the P2 section may be able to advise: https://www.volvoforums.org.uk/forumdisplay.php?f=19

tt82 · Oct 21st, 2017, 07:22

Moved to correct section.

The Edge · Oct 21st, 2017, 08:05

Needs a Vida session to see whats going on. My money would be a coil pack on its way out.

The other thing to do is before testing give it a good (legal of course) thrashing for 10 minutes or so to get everything hot.

Long term you might consider a terra clean session or equivalent.

MissSpentYouth · Oct 22nd, 2017, 08:22

I did give it a good session to clean things out and that improved things but still a fail.

If I had a faulty coil pack would that not cause my HC levels to fail as well ?

I have been though it with VIDA cant spot anything wrong with it at all :-(

davebb · Oct 22nd, 2017, 10:48

Hi I am sorry if it sounds silly , have you fitted a new air filter, sorry I have just seen that you have a new air filter,
Has it been remapped ?
Dave

davebb · Oct 22nd, 2017, 11:35

get the injectors tested and cleaned , is it running the stock injectors,
Dave

oragex · Oct 22nd, 2017, 12:42

You don't mention what mpg city/motorway does it get?

The following things can affect combustion/exhaust gases

https://www.youtube.com/watch?v=gOx3Q8vqoz4
leaking flexible downpipe
clogged PCV
coolant thermostat

+ 1 for the injectors with an ultrasonic cleaning machine, this will also help your fuel consumption so it's a good investment at these miles.
+ 1 for a VIda check

Whyman · Oct 22nd, 2017, 14:26

Had this on my wife's CRV a few years ago. Treated it with Forte injector cleaner and a good thrashing to clear it out. Also make sure that it is really well warmed up prior to the test ideally with one of the MOT stations that give appointments and make sure you arrive just before your time so it does not have time to cool down.

Since this one instance we have not had ant trouble again.

Whyman · Oct 22nd, 2017, 15:38

Duplicate post?

Oct 20th, 2017, 21:37	#1
MissSpentYouth Member Last Online: Oct 18th, 2022 09:26 Join Date: Jul 2016 Location: stroud	Failed mot on CO emissions tried everything stumped Hi All, I have a 2001 s80 2.4 20V petrol 170 BHP auto with 77K miles in brilliant condition runs perfect. Just failed its MOT on high CO about 1.5% were the pass mark is less than 0.3% so well over. Both HC and Lambda passed. Just one curious code on Veda which relates to the upper Lamba sensor heater circuit. Sure enough the Lambda sensor heater circuit was open circuit so I replaced it but was surprised to find the same error come back again shortly afterwards. One side of the heater circuit is supplied with a 12V feed where as the other is switched to ground through the ECU, seems my ECU might be faulty as it doesn't seem to ground out the heater circuit, so as a temporary fix I have disconnected the ECU and hard wired the heater to ground. Made no difference to my CO reading I don't think the heater circuit is required once the CAT is up to temperature. Things I have checked, plugs all good and the right colour, new air filter, smoke tested the induction system for leaks. MAP sensor readings look good and in spec as do the MAF sensor readings. Tested the PVC system with a glove over the engine filler all good showing a vacuum. Tested the purge valve no leaks. Checked the cam timing all good. The car only gets used a few times a week and for short trips so I took it along the motorway locked in 3rd for 15 minutes to cook the CAT this improved things significantly but still a fail about 0.8% CO. Put on a new after market CAT this made the CO worse back up to 1.5% so just fetched that off again and put the original one back. Just tried a new lower Lambda sensor in desperation and will do some more longer trips before taking back for testing on Monday. If I disconnect the lambda sensor i.e run the car open loop then I see about 0.8V from the sensor so the car would run rich left to its own devices. If I reconnect it the value drops to 0 as I think the ECU must load it up and use it in a current sensing mode rather than voltage but I could be wrong on this one. I am completely out of ideas on this one ? Car runs perfectly idle nice and steady no hint of a misfire, compression good, engine is mint as is the rest of the car. wondering if I could add a small air leak downstream of the MAF to see if that would get it to run leaner, however I would have thought the Lambda sensor would pick that up and just correct for it in any case.

Oct 21st, 2017, 07:19	#2
Simon Jones Premier Member Last Online: Jan 15th, 2022 11:23 Join Date: Feb 2009 Location: Salisbury (ish)	The chaps in the P2 section may be able to advise: https://www.volvoforums.org.uk/forumdisplay.php?f=19 __________________ 2008 XC70 3.2 SE Lux with LPG conversion - current 2005 XC70 D5 SE Lux - sold 2004 XC70 D5 SE Lux - written off by another XC70 2001 V70 D5 - sold 2000 V70 Classic 2.4 - sold

Oct 21st, 2017, 07:22	#3
tt82 Forum Support Team Last Online: Nov 28th, 2022 17:33 Join Date: Jan 2009 Location: Here.... obviously!	Moved to correct section. __________________ The more people I meet, the more I like my dog! 2009 V70 D5 R-Design - Jeade'en

Oct 22nd, 2017, 10:48	#6
davebb Premier Member Last Online: Apr 17th, 2024 19:02 Join Date: Aug 2013 Location: Emsworth,hants	Hi I am sorry if it sounds silly , have you fitted a new air filter, sorry I have just seen that you have a new air filter, Has it been remapped ? Dave Last edited by davebb; Oct 22nd, 2017 at 10:52.

Oct 22nd, 2017, 12:42	#8
oragex Premier Member Last Online: Jul 26th, 2021 21:24 Join Date: Jun 2013 Location: Coldnada	You don't mention what mpg city/motorway does it get? The following things can affect combustion/exhaust gases https://www.youtube.com/watch?v=gOx3Q8vqoz4 leaking flexible downpipe clogged PCV coolant thermostat + 1 for the injectors with an ultrasonic cleaning machine, this will also help your fuel consumption so it's a good investment at these miles. + 1 for a VIda check __________________ Several Volvo Repair Videos https://www.youtube.com/playlist?lis...ECTts0FSVSOT_c

Oct 21st, 2017, 08:05	#4
The Edge Senior Member Last Online: Apr 17th, 2024 21:22 Join Date: Jan 2011 Location: Birmingham	Needs a Vida session to see whats going on. My money would be a coil pack on its way out. The other thing to do is before testing give it a good (legal of course) thrashing for 10 minutes or so to get everything hot. Long term you might consider a terra clean session or equivalent.

Oct 22nd, 2017, 08:22	#5
MissSpentYouth Member Last Online: Oct 18th, 2022 09:26 Join Date: Jul 2016 Location: stroud	I did give it a good session to clean things out and that improved things but still a fail. If I had a faulty coil pack would that not cause my HC levels to fail as well ? I have been though it with VIDA cant spot anything wrong with it at all :-(

Oct 22nd, 2017, 11:35	#7
davebb Premier Member Last Online: Apr 17th, 2024 19:02 Join Date: Aug 2013 Location: Emsworth,hants	get the injectors tested and cleaned , is it running the stock injectors, Dave

Oct 22nd, 2017, 14:26	#9
Whyman Premier Member Last Online: Yesterday 11:10 Join Date: Nov 2013 Location: Newark	Had this on my wife's CRV a few years ago. Treated it with Forte injector cleaner and a good thrashing to clear it out. Also make sure that it is really well warmed up prior to the test ideally with one of the MOT stations that give appointments and make sure you arrive just before your time so it does not have time to cool down. Since this one instance we have not had ant trouble again. __________________ XC60 2013 D5 215 SE Lux Nav geartronic

Oct 22nd, 2017, 15:38	#10
Whyman Premier Member Last Online: Yesterday 11:10 Join Date: Nov 2013 Location: Newark	Duplicate post? __________________ XC60 2013 D5 215 SE Lux Nav geartronic Last edited by Whyman; Oct 22nd, 2017 at 15:40.

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