Our longterm Volvo C30 DRIVe, the super economy model, remains delightful to drive and for the past two months has ticked along with nary a whimper, except in one way. The Auto-stop system that switches off the engine when the car is stationary to save fuel, stopped working. We would pull up at a traffic light and the engine kept on running.

A look through the owner’s handbook suggested several possible reasons. The system automatically disconnects if the air conditioning has been running for a while. The Auto-stop won’t work if the outside temperature is over 30 degrees or below zero; if the battery only has a low charge and/or is running hot. Even running the interior fan at a high speed is sufficient to disengage Auto-stop.

None of the above applied in our case and the C30 DRIVe car was taken to our local Volvo dealer on the Gold Coast, where it operated normally…

Then the matter was referred to the tech chief back in Volvo’s Sydney head office. Finally it was resolved that we had only been doing slow speed short trips during the period when the Auto-stop refused to stop and that the trouble was due to the exhaust particulate filter cleaning itself.

These filters are devices that trap minute particulates that need very high temperatures to burn them off. Rather than running the engine hot all the time the particulates are stored in the filter. When the filter full and about to clog the electronics run the engine at a high temperature to burn the particulates out of the filter. During that time the engine is less fuel efficient than normal, hence the reason it’s only operated when necessary.

With the engine on our C30 DRIVe only being used for short periods it had to keep its temperature up by not shutting down when stationary. By one of those coincidences that frustrates all people involved in diagnostics our C30 finalised its particulate filter cleaning on its drive to the Gold Coast dealer.

Nevertheless it would have been useful if the owner’s manual had warned us of this. The technology is in its early days so won’t be at all surprised if the next edition of the owner’s handbook has been revised.

We have a confession to make, we no longer work at getting the absolute minimum fuel consumption as we did in the exciting early days with the super-economy car. It will be interesting to hear from owners of Volvo C3 DRIVe models about their continuing attitude to keeping the cars at their most economical. We feel that’s likely to be the case and it was only our revhead instincts as road testers that let us down. This possibly increased our consumption by a couple of tenths of a litre per hundred kilometres.

We haven’t had the chance to get away from the suburbs and heavy-duty commuting for weeks now and the average fuel consumption in these conditions is 5.8 litres per hundred kilometres. Which is still amazingly low when you compare it with the typical nine to eleven litres we have recorded from conventional petrol-engined cars in similar conditions.

Volvo C30 DRIVe remains a pleasure to drive, with strong engine torque and a five-speed manual gearbox that make it simple to use, even in heavy traffic. Volvo C30 DRIVe looks stylish in a more elegant manner than its competitors such as the Mini, Citroen DS3 and Audi A1. We feel the over-the-top looks of these are likely to fade as a fad before too many years have passed, but not ‘our’ pretty little Volvo.