The National Highway Traffic Safety Administration (NHTSA) has launched an investigation after “multiple fleets” reported issues with air brake systems which include vehicle fires.

In a July 16 NHTSA notice, the agency confirmed that an investigation has been opened into  Haldex Gold Seal GC3030LCW air brake chambers installed in model year (MY) 2015-2020 after complaints of air loss resulting in multiple vehicle fires.

An estimated 500,000 trucks could be affected, according to the NHTSA.

The agency describes the defect: “The power spring fractures, puncturing the diaphragm causing air loss within the springbrake circuit, resulting in brake drag without sufficient warning to the driver.”

According to NHTSA documents, 11 vehicle owners reported failure of a Haldex brake chamber “without discernable warning to the driver.”

In seven of those 11 cases, owners reported “thermal events causing extensive fire damage to the vehicle and, in some cases, the cargo too.”

“In at least one of the fires, a fire investigation report identified a wheel end fire as the origin. Analysis of other failed units found Haldex brake chamber diaphragms punctured by the power spring,” documents stated.

After receiving these complaints, officials “learned that multiple fleets were having issues with numerous vehicles. The Office of Defects Investigation (ODI) further learned that Haldex agreed to replace brake chambers on some of the vehicles in these fleets.”

The NHTSA investigation could lead to a recall.