Volkswagen said group production chief Michael Macht is quitting immediately, the second top executive to leave the automaker within a week.

Thomas Ulbrich, head of production at the carmaker’s main passenger-car brand, will take over duties from Macht on an interim basis until a successor is found, VW said in a statement.

Macht, 53, oversaw the production introduction of the automaker’s new MQB modular platform that is designed to cut costs and help VW Group’s global expansion. VW is increasingly relying on the MQB platform to deliver big savings by using more common parts across its range of brands and models.

But the drive to produce a greater variety of cars is proving tricky, particularly at VW’s main Wolfsburg factory, leading to delays in production of the top-selling Golf model and costly overtime

Company sources say Winterkorn has been unhappy with the production rollout of MQB within factories. This vehicle architecture enables VW to build cars with differing lengths, widths and wheelbases while at the same time reducing complexity and costs. More than 40 group models will be based on the same underpinnings.

Winterkorn said MQB is the “big competitive advantage” for the group and its stable of a dozen brands, but admitted it would require “tremendous effort” to implement the plan throughout the group.

The German news magazine Der Spiegel had reported recently that Macht’s position in the company was in danger after production equipment was installed at the cost of hundreds of millions of euros that did not function properly.

Macht’s contract, which would have expired in October 2015, was up for renewal in the coming months, just as the VW brand is instituting a €5 billion savings program to bolster its sagging profit margins.

VW has enjoyed a period of unprecedented growth, boosted by emerging market buyers of its upmarket Audis. Its sales have risen more than a half to 9.7 million vehicles in 2013 compared with levels before the financial crisis, and it is set to hit a 10-million sales target in 2014 – four years early. But the rapid expansion has led to a costly proliferation of models, especially at the VW brand.

Macht, a mechanical engineer, started his career with Porsche in 1990. He played a key role in integrating Porsche in the VW Group. In 2010, Macht was removed from his position as head of the Porsche brand and replaced by Matthias Mueller, who was seen as more of a visionary. Macht was moved to headquarters in Wolfsburg to take over responsibility for production.

Last week, VW’s global marketing chief, Simon Thomas, 54, resigned after just less than a year in the job.