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Old 08-10-2009, 09:29 AM
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Join Date: Jul 2009
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Default 940 lambda warning light

Have searched the forums for an answer to my problem but have yet to find one the same. Car (J reg 940s estate / manual box) has had mot and emissions are fine. Complete new exhaust fitted (N.B: The screw-in sensor (?) that fits into the side of the exhaust was reused when the replacement exhaust sytem was installed) but since then the lambda exhaust warning sensor dash light (orange) comes on usually after only a few miles and stays on until the car is parked for an hour or so. I say "usually" as there are times when I can drive nigh on a 100 miles before it will. At the same time, the trip meter (and milometer) tend to stick after a few miles. Pushing the trip reset button in can sometimes make the lambda light flicker on and off in rhythm to my pushing the reset button in, but not always. Sometimes pushing the trip reset has no effect at all on the sensor light.
Until recently, the trip meter (originally set back at zero) would only work for 2 to 3 miles before stopping (and consequently also the milometer) but a week ago I managed on a long journey to get well over 150 miles before the trip meter stuck AND before the lambda light came on! And there was me thinking it had all cured itself!!
How can these two faults be related? Surely one is mechanical and one electronic? Unless I have some debris or somesuch that has accumulated behind the speedo panel that is causing this?
The car is parked on the road, not used much - twice a week for short journeys - and I have had condensation build up in winter months behind the glass in the area of the trip readout.

One other problem the car has (which may or may not be related) is a "loose rattle" coming from under the car (sounds like to the rear) when going over uneven ground - sleeping policemen etc - which has never been sourced. No sign of it could be found by the fitters when raised on hoist when I had a new exhaust installed.

I understand there is a "speed sensor located in the differential" - where is this located and could this be the source of the trip meter problem? There is no pattern to the numbers upon which it stalls....so far, the trip meter has just exceed the 400 mile mark, in fits and starts.
The orange lambda sensor light on the dash still comes on after a few miles and usually will stay on till the car has been at rest for a few hours.

Does any of this sound familiar to anyone?
Is there a cure?

Many thanks in anticipation,

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Old 08-13-2009, 01:51 PM
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Thumbs up Lambda sensor light.

Following an incident where my 2.0L petrol 850 got flooded the Lambda light came on and stayed on (no change to fuel consumption) When the N registered car passed the MOT emissions test perfectly I asked the Volvo garage if they could re-set the computer which they duly did (without charge) light now off.
The Lambda sensor senses % Oxygen and plays a crucial part in determining the fuel/air ratio. It can be easily contaminated and so should be handled with care (RTM)
I doubt the trip meter problem is related but I could be wrong.
I donít know how the 940ís fuel management system works but I would check all the simple and obvious first; Plugs, leads, coil (good spark) Air filter (could affect mix if blocked) and only then swap the Lambda sensor for one that is known to work. Also ask Volvo if the FMS can be reset, in the 850ís case itís an OBDII plug in and a few key strokes on a laptop.

Hope this is of some use.
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Old 08-15-2009, 03:52 AM
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Or, you can just pull the codes from teh computer and go from there.

Regards, Andrew.
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Old 08-15-2009, 09:40 AM
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How long ago since you changed your MAF sensor? if not you may pull it out and clean it, then put it back and see if that helps.
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Old 08-16-2009, 07:32 PM
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Join Date: Jul 2009
Posts: 36
Default 940 lambda warning light

Firstly a very big thank you to all who have taken the trouble to reply to my posting.
Unfortunately I have no mechanical knowlege or experience and to make matters worse, the car came with no handbook so I'm a bit lost with some of the terminology you kind people are referring to.
History-wise the car has had a yearly service (at independent garages)since I purchased it 5 years ago....I wouldn't know where to start to locate the "MAF sensor"....is it something that would be dealt with during a service? Or where is it located?
Re the matter of the trip meter working sporadically, there has been this aforementioned unsolved "rattle" somewhere towards the rear of the bottom of the car for some time - when on a lift at the time of replacing the exhaust, the mechanic could find nothing anywhere on the bottom of the car that appeared loose. The rattle is most noticeable at low speed when driving over sleeping policemen etc. and sounds as though whatever is making the noise "is very loose"! I have checked for the obvious - no loose nuts and bolts in the spare tyre well etc.
I understand there is some kind of connection from the speedo etc to the back axle area ? Could this be loose and what is "rattling" and causing the speedo to occasionally stick? I have had incidences of both the trip / mileometer and the speedometer failing for varying lengths of time, although not both the trip and speedo at the same time.
The long term "sporadic" problem lies with the trip / mileometer - the speedo problem of incorrect speed readings (sometimes indicating 30 - 40 mph when the car was at rest!) hasn't reoccured now for several months.
Sorry to appear so ignorant - if the damn thing was a electric guitar I could strip it and reassemble / set it up with a blindfold on !!
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