With Vettel's dominance of F1 in jeopardy, Red Bull replaced the chassis with an old one he used during preseason testing, before starting practice at the Spanish Grand Prix this week.
"It's more a sanity check rather than a real problem with the other chassis," Vettel said. "So it's just to try everything we can, and basically reset and start again."
Vettel enters Sunday's race in fifth place in the standings with 33 points, far from Mercedes driver Nico Rosberg's competition-leading 79.
The massive rule book overhaul and the switch to V6 turbo hybrid engines this offseason has dislodged Vettel as the perennial favorite.
He has only one podium finish through four races, marking his worst start since joining Red Bull. His troubles have even led his team to order Vettel to let new teammate Daniel Ricciardo pass him in the last two races.
Vettel defended Red Bull's engine-provider, Renault, saying both team and motor-maker needed to share the burden of improving the car and increasing its speed in straightaways.
"It's not a big secret. If you look at the sector times or comparisons that we have available, we currently lose out too much on the straights, but there's always hope," Vettel said. "You have to look at it from the start. Where we started in winter, testing was unfortunately way, way off compared to where we wanted to be. Talking about the car, we set fire to the car nearly every run. Talking about the engine, obviously we were not on the same page that we expected to be, both in terms of reliability and performance.
"In the end we are a team, Renault and Red Bull Racing, so both parties know that we need to push very hard to make sure that we beat (Mercedes)."
While Red Bull may be grasping for answers, it has built up more than enough credit for designing the top car over the past four seasons for it to be ruled out of the running.
Mercedes' Lewis Hamilton has won the last three races to sit a close second to Rosberg. But he said he still had "Red Bull in the back of my mind."