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Mercedes Benz V230 1998 - High emissions, MOT failure - Fixed #

Posted by Luke Browne on October 8, 2011, 12:50 am

Year of Manufacture *: 1998-99
Engine Size and Code *: 111.978

Hi guys bit lost with this one?
Car sat for 6 months after an issue with the Air suspension compressor (now converted to coil spring) there are no driving issues or warning lights on dash. The car failed the Mot with rather high results. Wanted to be sure with this as the Cat is over £400!
Firstly code read which showed two reocurring faults as follows-
B7 Idle Contact Signal Improbable
30 Oxygen sensor heating Open Circuit/Positive
Short
Cleared but both soon returned. Scoped sensor to find the signal stuck at 1.2v? even introducing an air leak only got the signal down to about 0.6v and took a while to get there! Checked heater Voltage which is present when sensor disconnected but goes to 0v when connected, (I dont have pcm pin data to check back at control unit) Changed sensor due to slow switching but no change and same faults still log? Checked injection period which at idle is 2.4ms on all four cylinders (scoped). Am i overthinking this one when it just needs a new cat? Is It possible that the suspension compressor has damaged the pcm as when it came to me the fuse had been bridged by the RAC and was momentarily pulling 60amps when ceasing!! If i have missed an obvious test please enlighten me Emmissions are as follows( Thankyou and sorry for long post)
CO idle- 3.600-4.150 cruise- 5.800
C02 idle- 12.09% cruise- 11.24%
HC idle- 266 ppm cruise- 183 ppm
LAmbda idle- 0.887 cruise- 0.835
02 idle- 0.38% cruise- 0.08%

Re: Merc V230- very high emmisions!

Posted by Aidan birley <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT2879' width='330' height='300' border=0 style='border:none;'> on October 8, 2011, 8:07 am, in reply to "Merc V230- very high emmisions!"
Aidan Birley

Luke

This is NOT a Cat fault ! This is running to rich.

2 golden rules before considering condemning a cat are in my experience :-

1) lambda sensor must be reading / switching correctly.
2) Lambda emission reading must be within MOT pass limit.

The lambda emission reading is a calculated value and derived from the other measured gas readings taken. In theory it should be exactly the same inspective of if the cat is working or not(in practice I think the cat operation does make a very slight difference but it still should be within MOT limits)

Your readings show CO as much to high, I would expect to be under 1% even with no cat.

You must fix that Lambda sensor heater fault next as doubt it Will go closed loop if there is a current fault logged.

Cheers Aidan

Re: Merc V230- very high emmisions!

Posted by luke browne <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1817' width='330' height='300' border=0 style='border:none;'> on October 8, 2011, 1:43 pm, in reply to "Re: Merc V230- very high emmisions!"
Luke Browne

thanks for the reply aidan i did think it was unlikely to be the cat which is why i checked the injection duration which was ok? I did also wonder if it would stay open loop with a lambda fault logged, could this be enough to cause such high co readings even with respectable injection periods?? as i said before the heater wire (from pcm) has voltage until you plug in the new sensor so either high resistance or a short somewhere? really need the pin data to check at the pcm behind the head light so if anyone has this i would appreciate a peek!

thanks again for reply.
cheers

Re: Merc V230- very high emmisions!

Posted by aidan birley <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT2879' width='330' height='300' border=0 style='border:none;'> on October 8, 2011, 3:25 pm, in reply to "Re: Merc V230- very high emmisions!"

Luke
you need to fix that o2 sensor fault next.

AD has two wiring diagrams for V230,both different, but lists your engine code only as a vito

what tech info do you use ?

Cheers Aidan

Re: Merc V230- very high emmisions!

Posted by luke browne <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=UKAT1817' width='330' height='300' border=0 style='border:none;'> on October 8, 2011, 8:48 pm, in reply to "Re: Merc V230- very high emmisions!"
Luke Browne

i have autodata but didnt have access to it due to a pc issue! also have esi on the kts 650 but the pin out diagram for.the plugs didnt seem to match the cars plugs?? might explain the query with the engine code? think i need to double check all the vehicle info if the code says vito? will repost monday when i have checked info and accessed the pcm plug. thanks for your help so far

Re: Merc V230- very high emmisions!

Posted by Alan Lange <iframe src='https://members5.boardhost.com/ukautotalk4/info/user=ukat3293' width='330' height='300' border=0 style='border:none;'> on October 9, 2011, 7:09 pm, in reply to "Re: Merc V230- very high emmisions!"
Alan Lange

Hello Luke, as Aidan said, even without a cat the CO should only be around 1%. The only times I've had readings that high are when the wrong injectors were fitted or more often a vaccuum pipe was split. (Might explain the fault "idle contact signal improbable". Hope this helps, Alan.

Fixed #

Posted by Luke Browne on October 12, 2011, 1:42 pm, in reply to "Re: Merc V230- very high emmisions!"
Message modified by board administrator October 12, 2011, 1:58 pm

Fixed#
Thanks to all who posted and highlighted some issues with my knowledge of exhaust gases which i shall be addressing.
Went back to basics with this one and load tested heater wire earth on the 02 sensor which showed it as open circuit. Originally i provided this with what i thought was a good earth but there wasnt any current draw still but i now know that the earth i provided was no good! Whoops!
Anyway repaired earth and current draw shot up and the sensor began to switch perfectly! went straight through the emissions test with flying colours. Im still surprised that the vehicle could overfuel that much just whilst being in open loop with a respectable injection period?? Also the fault for the idle switch has not returned so must have been caused by the high sensor signal. Thanks for all the insight. Luke

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