Hyundai is recalling nearly 155,000 Sonata midsize cars in the US because the air bags may not inflate in a crash.

The recall covers cars from the 2011 model year. Hyundai says a short circuit in the air bag control computer can stop the seat belts from tightening before a crash as well as prevent the air bags from deploying.

The company says in government documents that it has four reports of air bags not inflating. It was not clear if anyone was hurt.

The cars were made between December 11, 2009 and Sept. 29, 2010.

Hyundai is still working on a fix for the problem. It expects the recall to start on April 20.