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Buying a brand-new electric truck is supposed to feel like entering the future. For many early adopters, the promise of EV ownership includes not just torque and tech, but also peace of mind. But sometimes, that dream gets interrupted by a single fault code that changes everything, and that’s exactly what happened to Leandro Nesi. He recently posted in the “GMC Sierra EV Group” on Facebook, sharing a frustrating experience with his 2024 GMC Sierra EV:
“It’s no longer the best truck I ever had. It looks like every single Sierra EV truck will have this problem. This is a 2024 VIN number xxx900. The error is related to the high voltage isolation. The vehicle will not charge so I left it at the dealer. Now I’m fighting to get a decent loaner.”
What makes this story particularly interesting is how fast his ownership sentiment changed. Just a short time ago, Leandro was enthusiastic about his Sierra EV’s capability. But that optimism turned to concern once the high voltage isolation fault made charging impossible. For a truck that costs as much as the Sierra EV does, being stranded at the dealership without a working fix or loaner vehicle definitely adds insult to injury.
Not Just an Isolated Incident
While this may sound like a one-off issue, I’m sadly seeing otherwise. Different owners are already reporting similar concerns, and Jamaal Baldwin was one of the first to reply to the post:
“Nice. I just went into the shop today for the same issue.”
It hints that we might be seeing the beginning of a pattern with early production Sierra EVs. If this turns out to be a manufacturing defect or design oversight, it could impact a much larger group of buyers than GM anticipated.
Rick Colbert then chimed in with insight that adds another layer:
“This is becoming a widespread problem. I finally got a fix for my 2024 Hummer. The battery cooling system has a couple of fittings that need to be replaced. Once that’s done it should work correctly. Message me and I’ll send you the part numbers. I also posted it in this form.”
It’s worth noting that the Hummer EV shares GM’s Ultium platform with the Sierra EV, which may indicate a shared vulnerability across the brand’s electric truck lineup. For owners trying to make sense of whether their truck is at risk, this kind of personal experience data is important to keep in mind.
Finally, there’s this eye-opening comment from Pablo JE:
“Two Sierra EVs so far and both have had multiple issues. I know this battery issue can’t be avoided. It’s going to happen sooner or later, but at this point I’m just waiting for more things to break so I can drop this brick at the dealer, get everything fixed, and be done with it for good. I’ve had it with this truck. Right now, I’m getting a trade-in offer of $85K.”
When you read about owners facing these setbacks, two trucks with failures like these stand in stark contrast to the energy surrounding other owners that test drove the Sierra EV and loved it despite having no EV experience.
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But What Is a High-Voltage Isolation Fault?
In simple terms, a high-voltage isolation fault means the vehicle’s onboard systems have detected that high-voltage components aren’t properly insulated from the chassis. It’s a serious safety issue, and as a precaution, the vehicle disables charging. This kind of fault can be caused by a number of different things including wiring damage, a bad component, or even an issue in the battery cooling loop which Rick mentioned.
These issues obviously become more alarming when they affect essential functionality like charging. For a truck marketed with long road-trip range and advanced tech, a failure to charge renders it completely unusable.
Expectations vs. Reality
Plenty of owners have jumped into this truck’s experience with high hopes. Some fell in love with the way the truck drives, having praised the Denali trim for its luxury ride quality and comfort, while others expected reliability and refinement on par with GM’s gasoline-powered HD trucks. Although honestly, even that last statement might not be true for many owners nowadays.
We’ve already covered cases where owners had back-to-back issues with their Edition 1 Sierra EVs and even reported that some of the truck’s advertised features weren’t active at all. That kind of inconsistency shakes trust in the brand’s first-generation EV lineup.
What strikes me most is that this isn’t just about a missed feature though. A fundamental trust issue in a new technology platform is not something that GMC needs. When someone spends over $80,000 on a flagship electric truck, they’re not just buying into a brand, they’re buying into a lifestyle shift. When that shift fails, it certainly leaves a lasting mark on owners and prospective buyers.
We know that GM has bold plans and that the Sierra EV is a big part of those plans. But bold plans need solid execution. If early adopters like Leandro are dealing with high-voltage failures and service delays, it begs the question: How scalable is this technology right now? And more importantly, how well is it being supported on the service side when things go wrong?
This hits harder knowing that some buyers even traded in reliable workhorses like the 3500HD to make the leap into EVs, as seen in this story about switching to a Max Range Sierra EV powered by solar. It sure shows commitment, but will the truck return that commitment?
Key Takeaways
- High-voltage isolation fault: This issue will render the Sierra EV unable to charge, potentially stranding owners.
- Early production VINs: Models ending in 900 seem vulnerable to this issue according to Leandro.
- Shared Ultium platform risk: The problem may be tied to the same platform used across GM EVs, including the Hummer EV.
- Loaner support challenges: Dealer loaners appear inconsistent, compounding the inconvenience for affected owners.
- Battery cooling fittings: Faulty fittings could be part of the problem, based on firsthand owner repairs.
- Buying considerations: If you’re considering a Sierra EV, make sure you understand the potential service timeline and warranty terms.
Let’s Hear From You
Do you think problems like this are just part of being an early adopter? Or are they signs of deeper engineering and service network concerns?
And if you own a Sierra EV or another Ultium-based GM EV, have you had any major issues with yours?
Aram Krajekian is a young automotive journalist bringing a fresh perspective to his coverage of the evolving automotive landscape. Follow Aram on X and LinkedIn for daily news coverage about cars.
Image Sources: The “GMC Sierra EV Group” public Facebook group and GMC’s gallery.
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Source: torquenews.com
