Faulty readings may have led to incorrect bills, says Southern California Gas Co.

Faulty readings on devices attached to automatic meters may have led to incorrect bills for tens of thousands of Southern California Gas Co. customers, utility officials said Tuesday.

While the gas company’s 5.5 million meters correctly recorded how much gas each customer used, the modules on about 1% of the devices underreported those totals. Gas officials said they still were working to understand the scope of the problem, which was discovered July 25.

It is possible that as many as 60,000 customers may have been underbilled.

For years, officials said, gas crews have been aware that some of the modules that feed information back to Southern California Gas Co. were prone to false alarms — going off even when they had not been damaged or tampered with.

“We’ve been aware of these false alarms for several years, but our early testing did not show any issues with measurements,” said Gillian Wright, vice president of customer services.

It’s unknown when the devices first started underreporting, Wright said. However, a sampling of the system’s meters — taken in July and August — showed the median difference between a customer’s actual usage and what had been reported was 20 therms. One therm costs a customer 80 cents.

Customers with the faulty devices, which are spread across the gas company’s service area, could receive bills to make up the difference between the amount of gas they used and how much they were charged. However, the Public Utilities Commission limits how far back the gas company can go in adjusting what residential customers owe.

“We actually have a very limited ability to go back and rebill,” Wright said. “We can only go back three months, and that means three months from July 25.”

The PUC also prohibits the gas company from sending catch-up bills if there is less than a 25% difference between how much gas was used by customers and how much they were billed.

Large commercial customers could be rebilled for the previous 36 months.

The PUC has an ongoing investigation into the utility’s billing system, a spokeswoman said.

“If rule violations are found, our staff could seek fines and penalties,” the commission’s Constance Gordon said in a statement.

Earlier this year, Southern California Gas customers complained of higher-than-average bills. Many believed the leak last fall at the company’s Aliso Canyon storage facility had resulted in price increases, but gas company officials said at the time that cold weather and longer billing cycles were to blame. Those bills are unrelated to the problems discovered last month, Wright said.

alice.walton@latimes.com

Twitter: @TheCityMaven

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UPDATES:

7:10 p.m.: Updated with information from a Public Utilities Commission spokeswoman.

This story was originally published at 5:35 p.m.