Metro passengers were caught up in delays yesterday when grit forced part of the line to close.
Network Rail say the fault at the level crossing in East Boldon - which was also closed to road traffic - was probably caused by road salt and grit.
South Tyneside Council say that it is written into their gritting procedure that they do not grit at level crossings.
The problems started at about 6.30am, according to Network Rail, which owns and maintains the line.
It was not cleared until after lunchtime, after its engineers visited the site.
A Network Rail spokesman said: “Just before 6.30am, we received reports of a track circuit failure, a system which monitors train movements, at East Boldon level crossing.
“As a result, trains had to slow down and call ahead to the signaller to ensure it was safe for the train to proceed.
“Engineers from Network Rail visited the site and train services are now running.
“We believe the track circuit failure was caused by salt and grit getting into the system where the road crosses the railway track.”
He added: “Network Rail workers were back on site last night to carry out work to try and prevent this problem reoccurring. We apologise for any inconvenience caused.”
The problem initially caused delays of up to 15 minutes between the East Boldon and Brockley Whins stations, before the service was suspended for just over 30 minutes between those stations while the problem was fixed.
A Metro spokesman said: “The problem affected all train services between Newcastle and Sunderland.
We understand from Network Rail that the problem was caused by road salts and grits getting into the circuit around the level crossing, which was causing the signals to turn to red.
“In the morning, trains had to be talked past the signals at very slow speed.
“Metro had to cancel some services and the other services were going through at very slow speeds, adding 10 or 15 minutes to the journey times.
“The problem started at about 6.45am, and it was at 11.55am that Network Rail made the decision to take the line down altogether.”
Earlier in the day, the service said people would have an extended journey time of approximately 15 minutes, with every third train not likely to run due to the nature of the disruption, with a knock-on effect on the system.
The spokesman added: “Thank you for your patience, and we are sorry for any inconvenience.”