Engine Light

[Alpinaman]

With a little bit of diagnostic kit this would be really easy to see and sort out..

I understand the logic in your thinking about the rear lambda fault on one cat,but unfortunatly the fault code only gives you a direction in which to look,not an answer...

The rear lambda's or the monitering sensors hardly vary in voltage when in use if the car is working correctly...If the rear lambda on either bank starts to vary in voltage in conjuction with the front lambda on that cat,then it indicates the Catalyst is faulty..
If the rear lambda see's exhaust gas outside of its set parameters then it will flag as a fault,but this fault can be set because the front lambda has gone faulty and pushing the rear lambda out of range.

Or of course it can be the rear lambda that is faulty.....But out of the 3 possible causes,the rear lambda is seldom the culprit..

In fact its usually a air leak or exhaust blow that flags lambda faults,but they are both easily negated..

[ian]

Thank you!

[Limbs]

Ian, I have had my car on a ramp this afternoon, mine is an S50 & only appears to have pre-cat sensors.

The good news is that the sensor cables take a round-about route to get to their connectors, so it would be easy to swap bank 1 & 2 sensors over, run the cables via a shorter route & temporarily tie them up for the purpose of a trial. Hopefully it would be possible for you to do the same with your post-car sensors.

[ian]

Thanks for that Limbs. Didn't realise that S50 doesn't have post cat sensors - an advantage over the S54!

I'm feeling that this is again leading to a post cat sensor failure that causes the dashboard EML (warning light) coming on - also not fitted to the S50 I believe?

Plan now is to try the cleaner Alpinaman has suggested. If this doesn't work, will get the sensors replaced - according to the mileage suggestion, think it's well overdue.

Will update outcomes as it seems likely all S54 owners will experience this issue in due course.

Appreciate the inputs guys,

Ian

[ZiggyCol]

Ian

I've got the same internittant problem and am following your lead thanks to Alpinaman. You may get there first so please keep us informed of progress.

Col

[ian]

Will do ZiggyCol - we can beat this!

[ian]

Added bottle of Forte cleaner (as referenced earlier in this thread) yesterday, as kindly supplied by Alpinaman. Also cleared the OBD2 fault code.

Will burn off the full tank of fuel with cleaner in a couple of days- will report back on developments.

Fingers crossed for a result, or its a new set of sensors!

[Alpinaman]

Glad it arrived safely Ian,

For best results put the cleaner in with 1/2 tank of fuel and go out in the car for a good ride,approx 30 mins on the motorway is ideal..

Keep the rpm's up(over 3000rpm as much as possible),so for example keep in 4th instead of 5th whilst on the motorway.Its all about getting the exhaust and lambda's as hot as possible whilst the cleaner is going through the system...

Fingers crossed it will clean up the sensors and it will sort your problems...

[ian]

Thanks Alpinaman, it arrived safely on Friday.

I do 100 miles most days in two 50 mile journeys - mainly at motorway speed.

Will keep the revs up as you suggest!

Cheers,
Ian

[ZiggyCol]

Also received Forte from Alpinaman and following his advice used it over the weekend. Couple of decent runs using 3/4 of a tank of fuel.

As is typical with intermittant problems my engine light has not been displaying itself over the previous week but it was prone to re-appearing. So no definitive correction through use of this but I'm hoping it will help prevent a re-occurrence.

[ZiggyCol]

Aaaarrrrgh !!!!!

Engine light back on this morning!

Can't think of any real correlation of factors to relate to it's appearance. It's very random nature would seem to suggest some sort of dodgy sensor so if I want to get rid I'll have to pursue that route.

It's only a small thing but it's just so irritating !

[MGR]

I haven't reads the whole thread so sorry if repeating.


I'd replace o2 sensors in exhaust. Most likely culprit.
Also have you checked the fuel vent valve in the tank, this can cause the EML to come on randomly and hard to diagnose.

[ian]

Unfortunately my light cam back on after 200 miles (2 cycles as the manual calls it).

Seems that sensor replacement is the likely answer.

Will get this done in the New Year.

[ian]

The plot thickens.

Had my car connected to a live data logger yesterday. The logger indicated faults on both banks.

All 4 sensors (one before and one after each cat) could be viewed performing. The post cat graphs were very similar to the precat ones. I'm told that the post cat graphs should be close to a straight line. This seems to indicate that the sensors are working but not of course that they are giving correct readings, albeit both were of equal value.

The verdict was that the cats are faulty (not withstanding that the exhaust emissions are fine).

Does anyone know if it is possible to check a cats performance independant of the cars electronics and (preferably) without removing it from the vehicle? I can feel a new cats and sensors solution developing here (at over £2K).

[Alpinaman]

No Ian,you cant...

Its a minimum of removing cats and even then you may not be able to see what the problem is..
Probably the cat material performance has just degraded..

Info is correct that the rear sensors should only indicate change very slowly in relation to the front sensors,and your correct in assuming that the cats are now knacked..

Only thing is that if the sensors are working fine then there is no real need to replace them...

Shame that its the cats that have gone....:(


Like i said a while back,with a little bit of diag its quite easy to see where the fault lies...