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Our Long-Term Chevy Blazer EV Has Another Charging Problem

We actually had to convince GM that something was wrong

2024 Chevrolet Blazer EV front
  • We're experiencing more charging issues with our long-term Chevy Blazer EV.
  • When connected to a DC fast charger, we've seen rates plummet to as low as 3 kW. The Blazer EV can pull up to 150 kW.
  • We brought our Blazer to a dealer multiple times so have the problem diagnosed and fixed.
  • Chevy offered an explanation and "fix" until an update is deployed.

It's been a month since I took our long-term Chevy Blazer EV to my local dealership for a comprehensive system update. Since the firmware update — and aside from a couple of random, one-time-only issues — we haven't experienced the flickering touchscreen, disappearing user interface overlay or temporarily missing colors we noted previously. However, a different problem has popped up, and one that required us to bring the Blazer back to a dealership yet again. This time, we've noticed that when plugged into a DC fast charger, the charge rate drops off quickly after we initiate a charging session. In practical terms, this means it takes a lot longer for us to charge the Blazer than expected. Buddy, are you ever going to be OK?

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2024 Chevrolet Blazer EV rear

Warning: Numbers ahead

The Blazer EV has a 400-volt electrical system capable of charging at up to 150 kW. When we first brought our Blazer to the dealership last December, we noted charging issues at that time: We only observed speeds near 150 kW for a few moments after connecting to the Blazer's charge port. It would drop precipitously from there. On several occasions, the DC charging session halted after only a few minutes.

The solution was to replace what Chevy calls the F-sensor. This sensor measures the ambient temperature. If the ambient temperature is too high, it throttles or disables charging to prevent damage to the battery. Our sensor was not reading the correct ambient temperature, which explains why the DC charging sessions stopped soon after we plugged the vehicle in.

For a few months, everything was going well. When plugged into a charger capable of offloading electricity at or above 150 kW, the Blazer's sessions followed a traditional charging curve: spiking initially before a gradual decline until the battery hit 80%, our charging limit for everyday driving. In March, I even drove it from my home east of Los Angeles to Palm Springs and back on a single 80% charge; I plugged into my nearby high-speed fast charger with 4% charge remaining and added 73.9 kWh of energy in just 45 minutes, for an average rate of 98.5 kW. These figures will be important in a moment.

I jumped back into the Blazer EV in May and noted no issues. Across several charges at the same station, the average rate hovered between 95 and 105 kW.

The fun begins (again)

The car went to other editors for a month, and I got into the Blazer EV again in early July. Its first charging event drew an average of 75.5 kW. Not great, but I started with 24% battery remaining, and batteries typically draw more power for longer periods when the beginning state of charge (or SoC) is low. I didn't think anything of it.

A couple weeks later, I brought the car into Puente Hills Chevrolet for the aforementioned firmware update. A week after that, I visited the EVgo station I use almost every time I charge an EV, and that's when I knew something was wrong. After charging at full strength for a few minutes, the instantaneous charge rate fell off a cliff once the SoC hit 55%. It bottomed out at 4 kW and stayed there. I waited for a few minutes to see if whatever I was experiencing resolved itself, but I ended the session prematurely after the electrical rate failed to rise. I chalked it up to a fluke and left the EVgo station.

It became evident there was a real problem during the next charge a few weeks later. I plugged into the same station, with 8 miles of range left and a 3% SoC — roughly the same circumstances as my post-Palm Springs charge back in March. But this time, the Blazer charged at its max capacity of about 150 kW for roughly 9 minutes before rapidly declining, falling to 28 kW just a few minutes later. All in all, adding 76.4 kWh took 77 minutes, for an average rate of 59.7 kW. Remember, the average rate back in March during a similar event was 98.5 kW.

2024 Chevrolet Blazer EV charging session

The next charge showed a similar charging curve. A max rate of 140-150 kW for the first few minutes, then a plummet to a dismal 3 kW. This event was accompanied by a bizarre message in the instrument panel that read, "Reduced acceleration. Drive with care," despite the fact that the car was stationary and charging. The charging curve is U-shaped, showing an eventual return to more normal — albeit reduced — levels of roughly 60 kW before the session was complete. With a beginning SoC of 21%, I added 59.4 kWh of electricity over 53 minutes, for an average rate of 67.5 kW. This is a slightly better average rate than the previous charge but still well off what the car is capable of and, crucially, incorporating a bizarre charging curve.

Could it be the charger's fault?

For consistency's sake, I used the same charging station unit every time I recharged the Blazer. Could it be that the unit itself was to blame, and not the car? The first piece of evidence that challenged the idea was the station's output itself. That EVgo station has a screen that shows the instantaneous electricity flow through all plugs that are in use. During the final charging event, the car parked next to me was plugged into the same unit, with the output of 350 kW split between two chargers. We were at similar states of charge — the Blazer at 53% and the other car at 51%. The Blazer was drawing 8 kW, while the other car was drawing 87 kW.

Soon after this charge, it was time for me to hand the Blazer EV off to another editor. I turned the keys over to senior reviews editor Clint Simone and switched into our F-150 Lightning. The Lightning's battery pack is much larger than the Blazer's, but it has a similar charging cap of around 150 kW. I charged the Lightning at the same station I used for the Blazer. Like the Blazer, its charging curve shows a high initial plateau before falling. But in the F-150, it peaked at just under 160 kW before falling to a minimum of 114 kW, which it sustained until the battery was charged to 80%. Its average rate was 130.2 kW.

The second Lightning charge at the same station was similar to the first: a quick climb to about 155 kW, followed by a gradual decline to a bottom of 99 kW with a slight uptick from there till the end. The average rate for this session was 112.6 kW. The beginning SoC for each Lightning session was below 20%.

At this point, I deduced that the charger itself wasn't the culprit. Clint hadn't yet initiated a charging session with the Blazer on his end, but I felt confident that something else was affecting the Blazer EV's charging performance. I asked Clint if he could take the car to a dealership out his way and see if they could find anything wrong.

2024 Chevrolet Blazer EV front

Back to the drawing board

Clint took the Blazer EV to Culver City Chevrolet, the dealer that helped us during the fiasco last December. He explained that on several occasions, the Blazer EV's instantaneous charging rate fell to single-digit levels for a sustained period of time for seemingly no reason. Clint asked that the dealer diagnose the issue and get back to us.

Clint delivered the Blazer to the dealer, and to its credit, the dealer did charge the vehicle with a DC plug and reported no unusual occurrences. However, the dealer's charger maxed out at 35 kW — well within the Blazer's capabilities, and we noted problems with charging at higher rates capable of delivering maximum (kilo)wattage. After taking in our concerns, the dealer explained it would have to get Chevrolet involved if the service techs determined there was indeed a charging issue. No problem, we've been down this road before.

The dealer contacted Clint a week after we first dropped the Blazer off. The car was ready for pickup, and frustratingly, the dealer had determined there was no charging problem.

As noted far above, we experienced charging issues early in our Blazer EV ownership. We had a faulty ambient temperature sensor replaced, which was supposed to solve the problem of reduced or stopped charging. But what if this sensor wasn't the root issue, or the sensor failed yet again? Our staff didn't note any charging irregularities until I took the car back in July, when LA was just starting to heat up after a relatively mild spring. To test whether higher temps were the trigger for the dismal charging rate, I'd have to take the Blazer somewhere warm.

With the Los Angeles basin set for highs in the low 80s over the next week, I decided to charge in reliably hot Palm Springs, which lies roughly 120 miles east of downtown LA. Temps would peak in the low 100s the following Monday, and there was an Electrify America station in nearby Palm Desert with a handful of 350-kW chargers that never seemed to be fully occupied. The plan was set.

Vindication

I pulled into the Target parking lot at 10:30 a.m. and plugged into the only open EA station. My phone's weather app showed the ambient temperature in Palm Desert was 96 degrees, while the in-car display read 99 degrees. The Blazer EV immediately pulled 150 kW, then settled down to 101-105 kW over the next 6 minutes. It remained there until 15 minutes after I started the session, when the instantaneous charge rate fell into the double digits. It dropped rapidly from there — 46 kW at 10:50, 35 kW at 10:51, 21 kW at 10:52 — before it bottomed out at 7 kW at 10:55. It remained there for a while, before climbing back up to 50 kW, where it stayed for the remainder of the charging session. I unplugged at 11:29. The Blazer had taken 61.3 kWh of electricity over its 19% to 80% charge, for an average charging rate of roughly 62 kW. My weather app showed Palm Desert at an ambient temperature of 99 degrees at the end of the session, with the Blazer displaying 109 degrees.

2024 Chevrolet Blazer EV instrument panel

A visit to the dealer

Shortly after the Palm Springs test, we reached out to Chevrolet to see if it could provide an explanation for the severely degraded charging performance. Chevrolet asked to have one of its service engineers pull data from the car to attempt to determine why we were experiencing this issue. We agreed to take it back to Culver City Chevrolet, where GM's engineer would pick up the car, extract the data and hopefully provide an explanation.

I dropped the car off on Monday shortly before noon and explained that, even though the diagnosis would only take a few hours, due to my personal schedule, I needed to leave but another staff member would pick up the Blazer when it was ready. My service adviser called me in the late afternoon and told me they were finished with the Blazer, and I informed him that I'd relay the message to the team and that we'd probably pick the car up the following morning. No problem, he said.

Editorial assistant Albert Hernandez was the hero we needed on Tuesday morning. He went to Culver City Chevrolet, where he had an unusual interaction with our service adviser. Albert expressed concern about taking our car back for a second time without a remedy to the issue we experienced. The adviser then told him that if we didn't pick up the car at that point, the dealer would start assessing a storage fee. Their explanation? Since our Blazer EV issue was being handled by GM, the dealer was merely facilitating the handoffs. The service engineer didn't communicate that a fix was needed, so Culver City Chevrolet wasn't really involved at that moment and thus would charge us a storage fee. To recap, this is the second time we've left this dealer with our broken Blazer, but at least this time, they didn't tell us everything was fine. They did, however, tell us we had to take the Blazer home or they'd charge us money.

Chevy Blazer EV rear three-quarter

Chevy's explanation

After parsing the charging data, Chevrolet explained: "The data our engineering team received showed your charging speed was reduced due to the frequent use of air conditioning while charging, which impacts charging speed when done simultaneously. In the interest of improving the experience for our customers who stay in their vehicles while fast charging (less than a third on average), an over-the-air update is coming soon to improve charging speed while the AC is engaged. For peak charging performance, our recommendation is to fast charge while the vehicle is off."

On one hand, it's good to know that Chevy recognizes there's a problem and seems to have an explanation and short-term remedy. We'll take steps to test the potential fix and verify for ourselves if exiting the vehicle while DC fast charging solves the performance issue.

But the idea that an active air-conditioning system is the sole culprit leaves me with more questions than answers. During the F-150 Lightning test many paragraphs ago, I charged with that car's air-conditioning system at full blast, and the instantaneous charge rate never fell below 99 kW. I've been charging EVs at the nearby EVgo station over the last year, and I always stay in the car with the air conditioning on. The Blazer is the only EV I've seen that has experienced a charging rate degradation to this degree, and this rate plummet wasn't noticeable during charging sessions initiated earlier in the year.

We'll continue to catalog our experiences as we experiment with charging the Blazer and the other EVs that make up our long-term testing program.

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