Peugeot Citroen said revenue came to €12.54 billion (£8.4 billion) in the July through September period, compared with €12.77 billion (£8.5 billion)a year earlier.
The group's earnings have suffered over the past two years from an aging vehicle model range and much higher raw material costs.
‘The level of sales in Western Europe will not allow the group to achieve a second-half operating margin in line with the first half of the year," PSA said in a statement, referring to the 2.4% target announced after its last profit warning in July.
Peugeot Citroen sold 1.7 million vehicles in Western Europe in the first nine months of the year, down 3.6%. On its home French market, unit sales fell 3.9% to 546,000 vehicles.
That compared with a 3.3% increase in unit sales in the rest of the world, to 766,000 vehicles. Sales rose 38% in China to 146,000 vehicles and 17% in South America to 156,000 vehicles.
The company did not publish quarterly figures by region, a geographical revenue breakdown or profit.