It only took 12 hours for hedge fund investor David Einhorn, a well-known Tesla Inc. critic, to wade into the controversy over the company’s solar systems.

He called on Tesla Chief Executive Officer Elon Musk to resign after a Business Insider report overnight showed the company tried to replace faulty parts in its rooftop solar panel systems as part of an effort known as Project Titan.

Earlier this week, Walmart Inc. sued Tesla, saying panels that the company’s energy unit installed caught fire on at least seven of its stores.

“How many solar panels are still defective and could cause fires?” Einhorn said in a tweet Friday. “A recall should have happened long ago.”

Tesla has proactively implemented a “remediation effort” to limit the impact a part known as a connector may have had, it said in an emailed statement. The company is unaware of any equipment manufacturer or regulator which has determined that substantial hazards exist. Over the past year, less than 1% of sites with such connectors have exhibited abnormal behavior, it said.

Its efforts include “replacing any faulty H4 connector at sites or adding failure detection hardware, and issuing a software update to ensure systems are turned off in case of failure,” Tesla said.

Einhorn’s tweet isn’t all that surprising given his short position in the company and how much his fund has profited from it. In April, he said “the wheels are falling off” for Tesla and has blasted the company’s electric-car business too.

Late Thursday, Walmart (WMT) said it and Tesla (TSLA) are in discussions to address the solar-system issue.