Toyota and the National Highway Traffic Safety Administration have determined that the cause of an intermittent stall in a very small number (68) of 2004 and some 2005 Toyota Prius hybrids was a software glitch in the Electronic Control Module (ECM).

Toyota has just announced a voluntary recall to correct this fault by introducing (flashing) new software into the vehicle ECU. This software update can be performed at any Toyota dealership. The recall also will include waterproofing of some electrical connections within the hybrid drive system.

Prius owners will be notified that they need to bring their vehicles in for a software update that will take from sixty to ninety minutes.

While the recall only affects the seventy-five thousand 2004 and 2005 Prius vehicles sold within the United States, Toyota has indicated that it intends to recall all Prius cars sold globally within the specified production range. This brings the number of vehicles to about 160,000.

The software glitch can cause a number of malfunction indicator lights to illuminate on the dash. If this happens, the hybrid control system will initiate a limp-in mode of operation that will shut down the gasoline engine and only allow limited vehicle movement using the hybrid electric drive motors. The limp mode is sufficient to drive the vehicle out of traffic to a safe stopping point. The electronically controlled and electrically driven brake and steering systems should continue to operate during this phase as well. In many cases, simply recycling the "start" button may reboot the system and allow normal operation.

Remember, this has only happened to about 68 vehicles out of a possible 75,000 in the United States.

The main components of the Toyota hybrid drive system include the inverter assembly, which sits directly above the hybrid transaxle (right side of engine compartment), and the gasoline engine, which is located on the left. Note the orange high voltage cables that supply the inverter with power from the battery pack, which is located in the trunk. The Electronic Control Unit (ECU) subject to reprogramming is located on the right side of the passenger compartment under the dash.

Additional information can be found in our July eNews "Let's Clear the Air" column.