Engine warning light mystery....

Hi there, I have a real dilemma and wondered if anyone out there may be able shed some light as to whats troubling my poor old V40 2.0T (2000 model phase II). Some time back my engine warning light came on, so I took it to an independent Volvo garage and they said MAF sensor is registering faulty, so I replaced it (MAF). Light still on, hmm... so took it back, had another diagnostics that came up breather box fault so had that replaced with associated pipe work... 20.9 miles (to be precise) down the road light came on again! Took car back, garage checked system and changed front oxy sensor on the exhaust... 20.9 miles down the road light came on again! Returned to garage checked system, replaced split breather pipe to turbo, garage took car on 15 mile road test said all was well... Well you've probably guessed what I'm about to say next, I drove down the road and at 20.9 miles on the clock and engine warning light comes on yet again. Well its back with my very patient garage and I am at a loss. Any response would be much appreciated. Thanks from a rather frustrated and perplexed owner.

I had issues with my engine light coming on. And thought it was a airflow sensor thing.(No fault codes showing though) The garage traced an iffy earth to the sensor which was giving problems. Or so they said. I had my suspisions that the car had been run on regular 95 unleaded just prior to me owning it (ie by the garage) causing mixture issues hence the light. After a fill up and a few miles on 98 Super Unleaded - no light and a happy T4. Maybe totally unrelated but just my experiences with the T4. Maybe get your car scanned for fault codes and go from there. Does it run ok? The T4 was fine when the light came on. I wonder if 21 miles is how far the car needs to go for self diaogonsis??

Kripps, I dont expect you to know but does this car have the EMS 2000 fuel system that we have here on our US cars ?, if so I believe they are not reseting the adaption values, if not done the system will still see the same fault. They may not have the function to do this with there scanner and disconnecting the battery or control unit we have found will not work . Hopefully a UK mechanic can add to my statement , Mister T.

I run my '02 T4 on standard 95 unleaded and have never had an issue - is there any reason why I would use 98 other than wanting a bit more performance? Cheers, Andy

Because you car is mapped to run higher ron fuel. By running 95 in it the car has had to retard the ignition timing to stop detenation in the engine. This reduces you mpg and power output from the engine. The extra cost of super unleaded wont cost you anymore as you will be travelling further on each tank of fuel. Be warned though as you ignition is retarded it will take 3 or 4 tank fulls of superunleaded for the ignition to be fully advanced again.

For the OP you need to get the codes read from you car rather than the garage just telling you whats wrong. It could be the other lambda sensor as alot of garages get them mixed up, you need the codes first though before trying it. Your car is OBD2 compliant so you could buy a code reader or laptop interface to read your own codes. Mister T this car will have the Seimens EMS 2000 ecu, i dont think it would be anything to do with adaption values though as he wouldn't get 20 miles without a light if nothing was wrong, thats my guess anyway.

I'll do it.....but am really surprised that the manual said it was fine to run 95 and the Volvo dealership when servicing and MOT'ing my car - wouldn't they have seen that there was a problem and told me? As it is the car goes great, and it gives good mpg.....can't wait to see the improvement. How much can I expect the mpg to increase? How much will it improve the power? Are you certain that there won't be any negative effects to changing the fuel to 98 RON? Sorry for all the question! Thanks, Andy

Hi Andy just checking back on the forum and wanted to firstly say thanks for the quick repsonse to my V40 problem and secondly for the advise. I thought I was pretty competant in sorting mechanical issues out but on the ECU side of things I'm at a loss. The car runs OK but having said that tonight the garage reported it was running a little rough. Well they have it now so I'll just wait and see what fault codes come up and take it from there passing on some of the very helpful advice I've received. Once again many thanks, Regards Rob

Hi Dandle, Thanks so much for your fast response and the advice, well the cars with the garage, I popped in tonight but they couldn't identify the problem. I think I'll pass on what members have suggested and advised and see whether that makes a difference. Its just frustrating as the cars been good for 15,000 trouble free miles for the last 3 years and suddenly this which I have to say is just a bit beyond me abilities to rectify, as I said to Andyg_prs, I'm pretty competant with the mechnical side of things but electrical/ECU issues are whole new Kettle of fish. Once again many thanks for your help, regards Rob