Dennis entered the Berlin double-header second in the championship standings despite having not scored a point since January.
The Briton qualified a strong fifth for the first of two races at the Tempelhof Airport Street Circuit this weekend and led at various points.
He was running sixth and attempting to pass Maximilian Gunther’s Maserati MSG machine in front heading into the Turn 6 left-hand hairpin when he lost control, collecting the Porsche of da Costa ahead.
After undergoing a system reset in the pits, Dennis re-joined and was classified 18th having also been handed a time penalty for the collision which he confirmed was due to a problem with the rear brakes.
Dennis was also left unhappy at Gunther’s actions under braking for the corner as he believes the German moved over to cover the line too late.
“The rear brakes came on in the end when I was spinning and obviously we need to see what caused the issue of not being able to stop,” said Dennis.
“The thing with Formula E is obviously because we lift so early it’s not like in any normal category where you can’t really move that much under braking because you’re already on the limit.
"In Formula E you roll for such a long period and then you brake, so you have the luxury of being able to move so much and I just felt like obviously he moved quite late.
“I was already committed and then I hit the brake and obviously had the situation. We just need to analyse why that happened.”
Da Costa was also eliminated in the collision after suffering damage to his left-front suspension, having impressively climbed from 19th on the grid to run fourth.
The Portuguese driver believes that despite having yet to activate his final Attack Mode, a strong result was on the cards.
He said: “We had an Attack Mode to take but the space would have been there for us to take it, potentially lose a place to Gunther, but we had more energy and pace than him anyway so for sure fourth, maybe a podium.
“Considering we started 19th, it would have been a very solid day.”
