2014 Cadillac CTS Vsport Long-Term Update 3
With Mike Floyd taking over as editor-in-chief of our sister publication, Automobile, I've assumed responsibility for Motor Trend's Car of the Year-winning, 420-hp, twin-turbo, long-term CTS Vsport. Poor me.
Unfortunately, Floyd's transition to the corner office went a little more smoothly than my transition into the CTS. Before I'd even taken possession of the keys, we hit a snag. In the middle of a road trip, creative director Alan Muir got an odd warning message: "Rear Axle System Off." While that certainly sounds bad, Muir reported no change in drivability or performance, and the warning quickly went away.
Once in my possession, I found that any good romp on the gas brought the warning back, but as Muir said, the car didn't behave any differently. Clearly, the rear axle was not disabled, so I figured it had to be something to do with the trick electronically controlled limited-slip rear differential. The car was due for an oil change anyway, so to the dealer it went.
"We'll have it done by tomorrow" quickly turned into a week-and-a-half at the dealer, which provided a 2014 CTS as a free loaner. Most of that time wasn't spent working on the car, though. It was spent waiting.
Per Cadillac's repair procedures, the tech first cleared the warning from the computer and gave it a test drive. The warning came right back. Next, he tried bleeding the differential's hydraulic system several times. No luck. At that point, Cadillac told him to replace the entire rear differential. Shipping a new one from Michigan took several days.
A new diff at 13,000 miles? The dealer was as surprised as you and me, and my service writer immediately began inquiring whether we'd ever drag-raced the car, because that would void warranty coverage for the replacement. (We hadn't.) Things weren't looking good.
Cadillac naturally came calling. The engineering team wanted to know the circumstances surrounding the warning message and the diff replacement. A few days later, I got a call from the CTS' chief engineer, Tony Roma. Here's what he told me:
The problem was a matter of porosity. The first 500 differentials shipped to Cadillac from its supplier contained a bad casting whose metal was too porous. The casting in question separates the low-pressure hydraulic fluid reservoir from the high-pressure reservoir. The bad casting was allowing the high-pressure reservoir to slowly bleed-down into the low-pressure reservoir.
The CTS' electronically controlled limited-slip differential uses high-pressure hydraulic fluid to quickly close the differential's clutches, evenly applying torque to both rear wheels under hard acceleration. The computer expects the fluid to be at a certain pressure for the sytem to operate properly. The bleed-down was causing the pressure in the high-pressure reservoir to fall below that expectation, causing the warning message to appear.
According to Roma, the real-world effect of this flaw is that the differential clutches engage more slowly than they're supposed to. And by "more slowly," he means it would take 250 milliseconds rather than 150 milliseconds. From the driver's seat, he said there would be no perceptible change in handling or performance in nearly any driving condition. The only way I would've noticed, he said, is if I'd been at a complete stop, turned the steering wheel all the way to lock, and floored the gas. Then, he said, I might have gotten a slight wiggle. I can't think of any situation in which I might do that on public roads, so it's hardly a concern.
Roma also said there was no danger of damage to the diff. At worst, the hydraulic pump would have to run a little more often to keep pressure up, which might shorten the life of the pump slightly. The warning message I received was actually designed to appear when the differential is getting worn out, somewhere at least 150,000 miles down the line.
There's more good news. See, our car is sort of a special case. The diffs that shipped with the bad casting were all used in laboratory tests, development vehicles, and press cars. According to Roma, only 50 to 100 of these diffs made it into finished cars, and all of those cars are owned by Cadillac (including our tester). There's virtually no risk, then, that any customer would experience what I did.
How, then, did I end up with a bum diff? The simple answer is the car fell through the cracks. Cadillac engineers first identified the problem more than a year ago in their development vehicles and most were fixed then. Ours, an early-build "journalist special," as Roma called it (it's equipped with only the performance options -- no sunroof or other upgrades that most customers will spec), was sent to us before it was identified as having the bad casting. Moreover, our car went nearly twice as far as any other before the warning appeared.
That's part of the reason Cadillac wanted the entire diff back. Had this been a customer car, Roma said, the dealer tech would have opened up the diff, replaced the casting, and all would have been well. In this case, Cadillac engineers had almost forgotten about the casting issue, it had been so long since it had arisen. They wanted the complete diff back so they could study it and make sure it was the known casting issue and not some new problem.
The be-all, end-all is that our problem was a rare one that shouldn't have affected any customers. Indeed, a lot of digging though Cadillac owner Internet forums and news articles failed to turn up any mention of differential problems in the new CTS. The roughly $4500 service was covered by the warranty, and our car is now as good as new.
During the service, we also had the dealer fix a problem with the tire-pressure monitoring system. Only the left rear tire's pressure was showing in the digital display, not the other three. The problem, oddly enough, was a bad sensor in the left rear wheel. A new sensor, covered by warranty, cured the problem.
The dealer also performed two recall fixes, one for the automatic-transmission shift cable and another for the windshield wipers. Both were handled free of charge.
In the end, the total cost to us was 10 days in a standard (and brand-new) CTS loaner car and no money out-of-pocket. Given how ugly things can get with defective components, we got off pretty light, and I'm back to enjoying the Vsport like nothing ever happened.
More on our long-term 2014 Cadillac CTS VSport: