The TTC wants to recover money lost to faulty Presto machines — it just doesn't know how much it's missing.

The transit agency voted Tuesday to launch a new study to find out how much the lost fares have cost them; when the results come back, the bill may just end up with Metrolinx.

"Presto's a lemon that we were forced to buy from the province," Deputy Mayor Denzil Minnan-Wong said after Tuesday's meeting. "It's been a horrible experience. It doesn't work, it's broken down."

Coun. Joe Mihevc called for the study into Presto's failure rate and how much Metrolinx, which runs the Presto system, should pay to make up for that lost revenue.

At any given time, the TTC figures that eight to 10 per cent of its Presto readers aren't working.

Once we have figured out the number we will send them an invoice. - Coun. Joe Mihevc, speaking of Metrolinx

Mihevc said he wants the TTC to develop a mathematical formula to calculate exactly how many fares are going unpaid due to the well-documented problems with the card readers.

With just 10 per cent of riders using Presto, he says the number might not be as high as some might think. But whatever it is, he said, Metrolinx will be responsible.

"Once we have figured out the number we will send them an invoice," he said, following the vote Tuesday. "And they will pay it."

TTC's initial Presto contract included that specific provision, Mihevc said.

Transit agencies still need to negotiate

Metrolinx spokeswoman Anne Marie Aikins says that while that may be true, the two agencies will have to work out some of the finer details.

"We are going to be negotiating that with the TTC as well so we're happy to discuss that."

Aikins says the system works reliably across the GO Transit system.

In the meantime, Metrolinx says the Presto readers are improving, but haven't yet reached the end goal of 99 per cent reliability.

TTC's contract with Presto runs until 2027.