The stock jumped 8.2% to $31.44 after ValueAct Capital notified federal regulators of the holding.
The rise comes after a roller-coaster year for LKQ's stock price. The shares were around the current level a year ago and slumped, recouped to around this point in late April, slumped, and rebounded again this month.
The San Francisco investment firm, which has pressured giants like Citigroup (C) - Get Report and utility PG&E (PCG) - Get Report , often takes seats on the boards of the companies in which it invests.
In a statement, the Chicago auto parts company said it "welcomes investment" and "regularly engages with stockholders to understand and assess their views and opinions.
"We appreciate constructive input and are focused on delivering enhanced value for all LKQ stockholders," the company said.
In the second quarter, LKQ beat analyst earnings estimates but also lowered its guidance for the rest of the year.
The company lowered its earnings forecast for 2019 to $1.73 to $1.81 a share, from $1.87 to $2 previously.
LKQ now expects organic revenue gains in parts and services of 0.5% to 2%, down by roughly half from its earlier estimate of 2%-4%.