The Federal Transit Administration (FTA) has issued a safety advisory for transit agencies that Phoenix Motorcars has issued a voluntary safety recall for certain 2019-2021 800V Catalyst and 2020-2022 ZX5 transit buses.

Phoenix Motorcars informed the National Highway Traffic Safety Administration (NHTSA) of a safety defect affecting Proterra 800V Catalyst and Proterra ZX5 transit buses with certain electrical and software architecture.

The vehicle controller software on these buses may allow the electrical circuit for the radiator fan to overheat, increasing the risk of a fire. Phoenix Motorcars has issued a recall of the affected vehicles.

Buses to Keep an Eye On

The buses were produced from December 14, 2019 to November 8, 2021, and July 21, 2020 to January 31, 2023 respectively.

According to the information provided to the NHTSA, the electrical connectors and terminals at one rooftop passthrough at issue in the recall are toward the maximum current limit that the terminals are rated for. This is causing radiator fans to run at 100% speed.

Over time and with higher ambient temperatures, the circuit design can result in excessive heat at the terminals and eventually the melting of “wedge locks,” which could result in a thermal event and lead to a fire.

A Quick Fix 

Software updates were previously released as a technical service bulletin. Phoenix Motorcars will redeploy this bulletin as the recall remedy.

The update will limit the radiator fan speed to 80%, reducing the load of each fan by approximately 46% and reducing the temperature at each terminal by approximately 71% above ambient without degrading the performance of the cooling system.

Phoenix Motorcars will provide this software remedy free of charge to owners of vehicles within the recall population.

Versions 4.10.2 or above contain the remedy. The version can be referenced on the vehicle’s dashboard.

The FTA recommends that bus transit agencies review their fleets to determine if they contain any of the affected transit buses.

If so, it is recommended that transit agencies download and update vehicle software. Bus transit agencies should continue to monitor their fleets for signs of overheating even after the update is complete to mitigate the risk of fire.

Owners may contact Phoenix Motorcars customer service at (909) 987-0815.

Questions or comments regarding this safety advisory are to be directed to Senior Accident Investigator for Transit Safety and Oversight Philip Herbert at (202)-366-5451 or Philip.Herbert@dot.gov.