BMW is adding nearly 185,000 vehicles to a 2017 recall for possible engine fires.

Two years ago the company recommended that the vehicles be parked outdoors until problems are fixed.

The recall expansion covers a dozen 3 Series, 5 Series, and Z4 models from the 2006 model year.

BMW says in documents filed with the National Highway Traffic Safety Administration that moisture can get into the cars' positive crankcase ventilation valve heater and cause plastic parts to degrade. That can lead to an electrical short and possible fire even when the engine isn't on.

The expansion brings the total number of vehicles recalled for the problem to about 925,000.

Dealers will replace the heater at no cost to owners. The recall is scheduled to start May 28.

BMW monitored reports from the field and found "several field incidents" involving 2006 3-Series vehicles, so the company decided to add to the recall from November of 2017, according to documents posted Thursday. It was not clear if those incidents were fires. Messages were left seeking comment from a BMW spokesman. Documents say that BMW is not aware of any accidents or injuries caused by the problem.

Vehicles added to the recall include the 525i, 525xi, 530i, 530xi, 530xi Sports Wagon, 325i, 325xi, 325xi Sports Wagon, 330i, 330xi, Z4 3.0i and Z4 3.0si from the 2006 model year.

In November 2017, BMW recalled over 740,000 vehicles from 2007-2011.

The PCV valve heater is designed to prevent the valve from freezing in cold temperatures, BMW said. But irregularities in manufacturing can cause corrosion and can lead to overheating.