A shortage of particulate filters forced PSA/Peugeot-Citroen to suspend production at four of its French plants last month.

PSA says it missed its January production target by 15,000 cars because of a shortage of filters, Automotive News Europe reported. The automaker is braced for further disruption in the next couple of months.

A scarcity of particulate filters may soon become an industry-wide issue as demand for clean diesel cars grows. Many models can only meet the stringent new 'Euro IV' emission regulations by using the filters.

The availability issue is crucial to PSA, which has pioneered the use of particulate filters on volume diesel cars. With one million filter-equipped cars since 2000, PSA is way ahead of other car makers.

Its nearest rival is Mercedes-Benz, with 110,000 filter-equipped cars sold to the end of 2004.

Assembly lines for Peugeot 307s and 807s, as well as Citroen C5s and C8s, were shut for a dozen days in total in January. PSA expects to be short of about 4,000 to 5,000 filters a month again in March and April.

The problem lies with a plant built by Japanese supplier Ibiden with French glassmaker Saint-Gobain in Courtenay, in central France to cater for PSA's needs. The plant cannot manufacture enough of the key ceramic components for the filters, PSA says.

The car maker, for the moment at least, has no other source of filters. Ibiden, which is 4.3% owned by Toyota Industries, declined to comment.

PSA found itself some 7,000 filters short. But its assembly line system works in such a way that even the production of cars without particulate filters was affected.

German supplier Robert Bosch estimates the worldwide market for particulate filters will reach six million units in 2007. That compares with 700,000 in 2004.