Hi,
Our car, an S-Max 2L petrol (2009), seems to have developed a fault but the garageââ,¬â,,¢s diagnostics are far from clear.
About 2 months ago the engine warning light came on and the local Ford garage traced it back to the temperature sensor in the CAT. They could find no fault in the CAT, so one possibility was that the temperature sensor itself was faulty. They cleared the alarm and advised us to see how we got on. If the fault came back soon then they said they would suspect the CAT itself. The car has been driving fine and now 2 months later the engine warning light re-appeared.
This time I took it to a completely different garage and they confirmed the warning again came from the temperature sensor in the CAT. They did emission tests and checked the exhaust system and all was confirmed to be OK with the CAT. However they noted that the car was difficult to start, unless the clutch was pressed in when starting the car. We may have got used to it but yes one usually has to rev it once or twice after starting the engine or otherwise the rev may drop. And in the first few minutes of driving the rev can go up & down a bit, sometimes causing the engine to race a bit, until the engine has warmed up when everything seems to be OK.
This, they believe is due to the Dual Mass Flywheel not working OK. They hypothesis is that if the flywheel doesnââ,¬â,,¢t work as well as it should this can cause unburned fuel to end up in the CAT, then when this ignites this caused the CAT to report a high temperature.
I am no car engineer and with the car otherwise functioning OK it makes it hard to justify spending the quoted Ã,£1300 repair for clutch & DMF replacement. They say there is a possibility that not doing the repair could impact the CAT and eventually damage it.
Has anybody else come across this problem, first of all of the car not always starting well, the engine RPM being up & down for a while and getting faults on the CAT temperature sensor? I see no other issues with the flywheel, no rattling or grinding for example.
Many thanks,
Hi any welcome along! I don't know the Ford engines anywhere near as well as the VW ones but I don't understand their theory at all - a dodgy flywheel shouldn't (personally, I'm inclined to say couldn't) cause a fueling issue on a modern car unless it was seriously degraded and to that end you should be able to feel and hear it!!
Now, on the other hand if it is overfuelling then that bit is correct - unburnt fuel will cause premature CAT failure. I'm slightly confused here - Have they changed the sensor in the cat? In reality two warnings in 2 months isn't likely to do much damage at all.
I'm of the opinion you have something else causing the issue, there are a number of things on a petrol that could cause the issues and they may or not be linked together but I personally think the DMF has little to do with it!
Looking forward to the opinions of the others...
welcome5
im sure ive read somewhere that starting problems can be caused by the dmf breaking down,hence more cranking etc,cant remember if it was for the tdi or the petrol versions.
but the consensus was that most just put up with it,unless your pockets are flush.
what voltage is the battery?,you can do an onboard diagnostic check by the way.
It's a new one on me, as I understand it the upstream and downstream 02 sensors for the catalyst don't have temperature sensors in them, though they do have heating circuits to speed up their response time from cold- see the 'Heated Oxygen Sensors' section here. (http://www.picoauto.com/applications/lambda-sensor.html) It sounds to me from your description that the fault you mention may be the heating circuit failed in one of the oxygen sensors, which can cause a warning lamp to illuminate. That's where I would be looking first, at least regarding the warning lamp- an oxygen sensor is a lot cheaper and quicker than replacing a flywheel and clutch, or catalyst for that matter! Whether a defective sensor would be responsible for the vehicle being hard to start from cold is another matter, it sounds like there may be more than one issue here.
EDIT- My understanding of catalysts on recent vehicles may be a little out of date, though a quick scan through of the parts diagrams didn't show anything other than the upstream and downstream oxygen sensors in the area of the catalyst on the 2 litre petrol S Max, unless any separate temperature sensor fitted is part of the catalyst (i.e, not removable) which would require renewal of the complete catalyst to replace or the catalyst temperature is calculated by the engine management by comparing the exhaust gas oxygen content upstream and downstream of the catalyst.
Vaguely remember reading something between the DMF and the crank position sensor although it doesn't appear related to the current fault code
Thanks Mirez, gregers, insanitybeard and Chrispb for your information, most useful.
My secret hope is that it is a faulty sensor. I see none of the symptoms that are reported as related to failing dual mass flywheel, and the CAT gave good emission readings. Surely, a DMF failure would be noticed.
Maybe I just have to wait and see, and hope that the CAT temperature sensor doesn't often raise a warning. Driving with a warning light on is not something I like to do as it could be another fault.
And I need to find out why it is sometimes difficult to start, and starts better with the clutch pressed in, and find out why the RPM is going up & down for the first ~3-5 minutes after driving off in the morning.
Not had any dealings with MK3 petrol Galaxy's but generalising with the hard to start erratic idle,sometimes a faster idle and high cylinder temperature could be down to a vacuum leak on the intake manifold or associated pipe work.