Nissan North America said a key communications system that Nissan and Infiniti dealers rely on for several critical operations has been restored.
The system -- which helps dealerships order cars and parts, obtain product rebate information, check on recalls, and file warranty claims -- was fully operational as of 7 p.m. EDT on Wednesday, the automaker said.
A power outage on Saturday at a Nissan North America data center in Denver had shut down the system for about four days.
Most Nissan communications systems in the U.S., Canada and Mexico were affected, the automaker said.
Some operations had been restored during the day on Wednesday, Nissan said.
"Some of our dealer business applications have run in a reduced capacity using manual processing," Nissan said on Wednesday.
The outage hobbled Nissan and Infiniti dealer operations, leaving them unable to report sales, process warranty claims or locate available vehicles at other dealerships.
"I've never seen anything like this," said Dave Wright, dealer principal at Dave Wright Nissan-Subaru in Hiawatha, Iowa.
Dealers also couldn't check up on customer payoff information from Nissan Motor Acceptance Corp., the automaker's finance arm, Wright said.
"I have had three customers today become irate," he said earlier this week. "We look like idiots because we can't tell them what incentives they are eligible for, even how much they have left on their Nissan lease or finance note."
The NNANet system has gone down for a few hours in the past, but it's never been down for more than a day, said Tim Hill, owner of Hill Nissan in Winter Haven, Fla.
"Everything we do with Nissan goes through NNANet," Hill said. "That is our lifeblood."
Mario Murgado, owner of Infiniti Stuart in South Florida and chairman of the Infiniti National Dealer Advisory Board, said the company worked around the clock to fix the problem.
The system crash had been a frustration for many dealers, but it could have been a bigger problem if it had lasted until the end of the week, Hill said.
"That's when dealers receive their weekly incentive payments," he said.
The outage still came at a particularly bad time: Dealers typically book most sales in the back end of the month.
The service interruption also could have posed a safety risk for customers because it prevented dealers from looking up potential safety recalls and advising consumers about whether it was safe to drive vehicles, Wright said.