DETROIT – Volkswagen faces daunting challenges in fixing software that enables cheating on diesel engine emissions tests, a task that’s becoming more urgent because of growing anger from customers.

The company has set aside $7.3 billion to pay for the scandal. But experts say it’s likely to cost much more as VW tries to comply with U.S. clean air regulations while appeasing diesel owners who paid extra for the cars, thinking they could help the environment without sacrificing performance.

“We understand that owners of the cars affected by the emissions compliance issues are upset,” VW said on a consumer website launched Sunday. The company asked for patience and said it would address the issue as fast as it can. A spokeswoman wouldn’t comment further.

But experts said VW will have to strike a careful balance to appease government regulators, make customers happy and avoid emptying the company cash box. A cheap remedy of software fixes likely would hurt performance and gas mileage, further antagonizing customers. A more expensive fix that adds a treatment system wouldn’t hurt performance, but it would cost thousands per car and by one analyst’s estimate, could total more than $20 billion including vehicles in the U.S. and Europe.

That’s in addition to a potential $18 billion fine in the U.S. and the cost of numerous class-action lawsuits alleging that VW’s cheating reduced the value of its customers’ cars.

The scandal broke on Sept. 18, when the U.S. Environmental Protection Agency and the California Air Resources Board accused VW of installing secret software on 2-liter four-cylinder diesel engines that turned on pollution controls for lab tests and shut them off during real-world driving. As a result, 482,000 Jettas, Beetles, Golfs and Passats from the 2009 to 2015 model years belched out 10 to 40 times as much ozone-causing nitrogen oxide as U.S. law allows.

A few days later, VW admitted the same “defeat device” that switched the pollution controls on and off was on 11 million cars worldwide. Germany says 2.8 million cars there are affected.

Software in the main engine control computer figured out when the cars were being tested on a treadmill-like device called a dynamometer that the EPA used for verification and turned the controls on.