Nico Hulkenberg says Renault's reliability is not good enough after a DRS issue forced him out of the Japanese Grand Prix when he had points in his sights.
Hulkenberg has suffered several power unit reliability issues this year, and retired from a good position in Monaco with a gearbox problem.
At Suzuka, his DRS stuck open into Turn 1 when he was behind Romain Grosjean, and he was forced to pit.
His mechanics tried to use brute force to sort the problem out, but without success.
"Normally when you go off the throttle or de-activate it, it comes back down," Hulkenberg told Motorsport.com.
"In this case it got stuck open because there was a metallic shim part that was broken, so it sent that hydraulic mechanism out of order. It was blocked, basically.
"It happened into the first corner. It felt a bit weird, then another corner a bit weird. I thought this is dodgy!
"Then I looked in my mirrors and saw it was open, and that was clear. It was not so good in Sector 1, to be honest, a bit scary!"
Hulkenberg says that the Enstone team has to focus on reliability: "Absolutely, it's not great. But it's part of the whole development that we go through.
"It showed one weakness again, and the car often is not good enough reliability-wise, and also performance-wise of course. There's still plenty for us to work on."
The German was convinced that he could have finished as high as eighth.
"The race went pretty well. We started on the harder compound and did a long first stint, so we did a reverse. It worked quite well, but I made my life harder by making a mistake in Degner Two, where I ran off and went through the gravel and lost four seconds.
"I think otherwise I could have pitted and even have come out ahead of that group, Massa and the Haas guys. In the race the car was actually pretty decent. I was about to overtake Grosjean when the DRS problem happened."