I have a problem with my Jan '05 Signum Design 3.0 CDTi which essentially makes it unusable. The garage have been pretty good but have been unable to locate the problem which has so far been intermittent. I would welcome your comments if anyone has experienced the same or knows what might be wrong.
Two years ago, under warranty, it spent over two weeks in the workshop and showed consistently clean on a full diagnostic until the Service Manager eventually found a fault with the air flow meter - using a digital multimeter as it turned out, rather than the full garage diagnostic kit. Air flow meter was replaced and car was mostly ok, very occasionally faulting in wet weather but resetting if the key was removed. I was pretty sure something still wasn't right but it was so intermittent I could never reproduce it on demand - until now.
I have seen the fault more in cold and wet weather, usually when the engine is just warming. If I accelerate (not necessarily firmly) the spanner light comes on and the engine loses power just as I release the throttle. This is accompanied by a whistling noise which I believe may be the overboost valve releasing air from the turbo. The power is so low that if I bury my right foot in the carpet in third gear, the maximum speed I can achieve on the level is just over 30mph. Most of the time I am afraid to overtake or pull into traffic in case the car decides to drop 90% of its 170-odd horse power and leave me stranded at lawnmower speed on a busy road.
When the car is in the fault condition, the alarm / ultrasonic light on the console comes on and the car will not dead-lock or alarm (second press of fob is not recognised). I can reset the fault by removing the key, opening and closing the driver's door, fully locking (2 presses) and unlocking the car, then reinserting the key and staring the engine. Does anyone know of a connection between the body control units (door locks & ultrasonic sensors) and ECU which would cause both to fault simultaneously?
The garage have not yet identified a definite fault but are preparing to quote me for a replacement air sensor. I don't want to do that without a proper diagnosis but I might have to take it because the car is pretty well unusable, arguably dangerous in its current condition. However I am very open to suggestions if anyone has a better idea.
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