TOKYO -- When the next-generation Prius hybrid came up for final approval at a session of top brass, Toyota Motor Corp.'s global r&d boss delivered bad news to the car's chief engineer: The design doesn't cut it. Try again.

The fateful review, according to a source, happened last year, prompting a whirlwind of tweaks by Prius Chief Engineer Koji Toyoshima. Only when the restyled car resurfaced for a yay-or-nay at an April meeting did it finally get the green light.

Mitsuhisa Kato, the executive vice president who nixed the early design, said other issues played the pivotal role in a decision earlier this year to delay the launch of what is arguably Toyota's most iconic nameplate.

It's unclear what those issues were. But it's clear from conversations with Toyota executives that a less-than-great design was not going to be approved.

Toyota President Akio Toyoda has prioritized design like never before. And the founding family's scion has recruited like-minded executives to do likewise. So the order to overhaul a nearly finished fourth-generation Prius -- while still a rare rebuff -- highlighted the new mindset.

"The design redo was instructed by myself, and the president said the same thing," Kato told Automotive News. "We substantially refined the design, and we have finally reached a level where we can offer it next year."

As reported by Automotive News, Toyota decided to delay the start of production for the much-anticipated Prius to the end of 2015 from an initial target of next spring.

There are plenty of potential hang-ups. The upcoming Prius will be a critical test bed of complex new technologies, including the carmaker's modular vehicle architecture and next-generation hybrid system.

Getting the look right, executives hope, finally will free the Prius from its frumpy image. Toyota, which sold more than 1 million hybrids in 2013 for a second straight year, has more riding on the Prius' redesign than bragging rights. It also will show whether Toyota's new design strategy is on the right track.

Toyota is closely guarding styling details of the next Prius, code-named 690A, and its plug-in variant, code-named 680A.

But Toyota's design studio aims to inject emotion into a utilitarian hatchback that traditionally has tapped customers' environmentally conscious, rational side, said one engineer.

The last-minute course correction in styling apparently delivered big changes. "The exterior is clearly different," said a Toyota insider. "We want designs that feel like a fresh breeze and have impact."

Toyota also is expected to better differentiate the designs of the standard Prius and the Prius Plug-in this time. Currently, both vehicles share nearly identical bodywork.

Toyota aims to restyle the standard Prius with a sporty look targeting younger buyers and give the plug-in version a more staid look to appeal to a wider audience, according to a source at a company that supplies parts for the vehicles.

The concept car most closely previewing the next Prius is the C-HR Concept shown at this year's Paris auto show, said another source. While the concept is a compact crossover, its so-called diamond architecture features, such as the muscular wheel arches, aggressive grille and tapered glasshouse, are expected to influence the looks of the Prius hatchback.

Kato: Prius finally at right level of design

More flexibility

Another source added that the Prius takes advantage of Toyota's new modular C platform for a low center of gravity, lowered hood and smaller front air intake. It gets a sportier stance, higher rear end and more pronounced wedge shape.

Because of the new platform, engineers also will have more flexibility in designing the interior. While the overall dimensions of the car are expected to remain roughly the same, the next Prius will get more cabin space, one source said.

To maximize aerodynamics, the next Prius will keep the current generation's split-level rear window, despite visibility issues.

To eke out better fuel economy, the next Prius also is expected to ramp up the use of lightweight body parts, the supplier source said.

The standard Prius is expected to get more aluminum sheet metal while engineers are contemplating some resin, or plastic, body panels for the Prius Plug-in. The current Prius and Prius Plug-in already have an aluminum hood and rear hatchback door. The only mass-market Toyota vehicle with plastic body paneling is the Corolla Fielder, a Japan-market wagon with a resin rear door.

The next Prius is expected to keep the center-mounted instrument cluster that Toyota is making a hallmark of its alternative drivetrain lineup. The setup, which centers the speedometer in the instrument panel almost below the rearview mirror, also has been used in the Mirai hydrogen fuel cell sedan that goes on sale in Japan today, Dec. 15.

One new design feature the Prius apparently won't emulate is the Mirai's external styling, with its flared and flowing fenders, wild front air intakes and angular upright stance.

"When we came up with this, Prius designers said they wanted to borrow from it," said Toshihiro Kasai, the Mirai's deputy chief engineer. "But I said, 'No, this is just for the fuel cell vehicle.'"

New mindset

Under global design chief Tokuo Fukuichi, both the mass-market Toyota brand and its Lexus stablemate have undergone a design renaissance. The new looks are intentionally polarizing, aiming to err on side of yeah or yuck, rather than yawn.

Fukuichi injected pizzazz into Lexus with its aggressive spindle grille and has spiced up Toyota with the likes of the head-turning FT-1 sports car concept. The contrarian design guru also was the main champion behind the dramatic midcycle freshening of the 2015 Camry that required nearly all-new sheet metal.

His efforts were rewarded this year with a promotion to the board of directors, a first for any design chief at Toyota. He also was named a 2014 Automotive News All-Star for global design.

Engineers say Fukuichi is pushing the company's gearheads and bean counters to think more with the right side of the brain.

But some habits still die hard. Toyota's design process was constrained by groupthink and design by committee. The new mantra: Get individuals to make bolder stands.

So Toyota's top brass is making the hard calls, even at inopportune times, in order to lead by example.

"Especially when it comes to design, only a few people make critical comments. Probably the president and I are the only ones, or Fukuichi-san, head of design," Kato said. "We share the same mindset. We're the ones who say the design is no good; take the time to do it over." c