Luxury car-maker Mercedes-Benz faces huge embarrassment over a revolutionary new engine, with thousands of customers reporting that their vehicles have broken down.
The German firm has so far not issued a formal notice to buyers of certain E-class and C-class cars, which can cost between £30,000 and £75,000, that the vehicles may have a fault. But with the number of breakdowns rising, the car-maker may be pressed to come clean about the extent of the problem.
The fault concerns fuel injection systems on an all-new diesel engine, which was hailed as having undergone some of the most rigorous testing ever conducted by a car-maker.
It is thought that in Germany at least 2,800 customers have returned their cars for repair. Latest figures for the UK are about 550 vehicles.
One Mercedes engineer estimated that, worldwide, up to 50,000 vehicles may have to be repaired, which is a blow for a company which prides itself on reliability and quality.
The faulty fuel injectors, made by the giant US-based component company Delphi, were part of a new generation of "greener" diesel engines. Problems with the injector's electrical system mean cars either go into emergency mode, restricting speeds to about 47mph, or fail completely and the cars stop.
British Mercedes' customer Frances Thapar, whose E-class stalled completely, said that the carmarker should be more proactive. "We understand that thousands of cars are affected. Mercedes should be making an announcement to forewarn people."
The OM 651 engines were launched last year in a blaze of publicity, with Mercedes saying that the powerplant set new standards in fuel consumption and CO2 emissions.
The engine and fuel injector underwent 10 million kilometres of testing in temperature conditions ranging from the burning desert to the arctic environment.
A Mercedes spokesman denied that there was an attempt to play down the problem: "When the fault occurs it is dealt with, while other cars can be checked when they are serviced."