The mysterious electrical problem in which power surges were doing damage to BART's aging fleet of trains last year appears to have returned, and once again train cars were damaged Friday by surges between Pittsburg-Bay Point and North Concord stations, leading to systemwide delays.

As ABC 7 reports, the trouble began around 10 a.m. Friday and continued into the evening commute. In total, 22 train cars had to be taken out of service, and BART still has not identified what's causing the surges — calling to mind this exact same drama that began in March 2016 and took upwards of 50 cars out of service. That mysterious problem disappeared a month later with no explanation, and BART subsequently spent $2.5 million on outside consultants and others trying to diagnose the problem and prevent it from happening again.

BART spokesperson Jim Allison tells ABC 7, "We haven't decided [if] this is the same problem, but there are some similarities so in an abundance of caution we are taking a closer look at this."

Allison explained that the problem seemed to affecting only longer trains, so BART began using shorter, five-car trains instead to shuttle passengers between North Concord and Pittsburg-Bay Point.

BART officials say they don't know when the problem may be resolved — and last year this led to months of slowed service due to the number of damaged train cars and the difficulty of finding replacement parts for them.

Previously: Despite Spending $2.5M, BART Still Doesn't Know What Caused Mystery Voltage Problem