Our 2022 NX 350h experienced what smelled like overheated brakes while climbing 4,000 feet in 13 miles (Lone Pine to Whitney Portal in CA). I obviously didn’t use the brakes on the way up and the temperature gauge didn’t budge. It was stronger on the passenger side front area. Any thoughts on the culprit? Other than that the NX handled Death Valley and points in between with no issues. As an aside, as part of the 60K service I had the coolant a nd brake fluid replaced last week before the trip. Any thoughts would be appreciated.

 

Doesn't 100% mean it can't be brakes, I've learned from previous hybrid experience the brake calipers can get a bit sticky over time due to lack of use (regen) without regular servicing. My Camry Hybrid starting burning up the rear brakes for just such a reason. I was a real hyper-miler and prided myself on barely using the brakes so max regen all the time. However, that would not be a symptom of climbing, as it would happen all the time (unless, while climbing speed and wind were more likely to reveal the odor). Easy way to tell, if you have an infrared temperature gun, take a short drive when car is cold without using mechanic brakes then measure the temperature of the rotors. If they get very hot, it may be due to a stuck caliper. I learned the harder way on my Camry Hybrid, touched the rotor, Ouch! Super hot.

Also, by chance just had an oil change right before your trip. Sloppy tech, some splashed about that got burnt off?

 

Recent service for any fluids may have resulted in the fresh fluid being dripped on any number of items under the hood that would heat up during harsh use, even antifreeze. Plus the process of draining fluid from under the car can be extremely messy, as right when the drain plug is removed there's a strong stream, a rush of the fluid out of the drain hole, it can go anywhere nearby. If the tech didn't take the time to clean off every last wet spot it could smell once heated up too. I make a point even if I didn't do the work, to get the car outside on the drive at home and carefully spray water around the areas that may have seen spills. Thus diluting the remnants of the spilled fluids. Most likely some brake fluid may have been left on brake calipers right near the bleeder valve where the fluid comes out when serviced.

Other possibilities are plastic bags and other flying debris on road getting trapped under the car and possibly contacting the hot exhaust. Plastic bags stink real bad and slowly roast on an exhaust pipe for a while before it goes away.

When inspecting for hot brakes, the fronts do most of the work, start by getting close to wheel and sniff, brake pads smell bad when they're hot, touch the metal rim - alloy wheel - around where the wheel bolts are, quickly at first then if it's not roasting, put your hand on it to get an idea of it's temp, then quickly go to other wheel and do same. Stay away from touching the rotors they get VERY HOT! If brakes are really hot they may even smoke a little bit too.

Your recent trip obviously really worked the engine, everything really got a good heat soak. But, nothing has indicated it's not running well, no overheating warning on dash etc. Check brake fluid reservoir on level ground to make sure it's sitting at full level to be safe, but keep in mind your motor generators are doing almost all the braking at speed, the brake pads and rotors are typically only called upon when your almost stopped, around 5 mph, so your pads should be ok I would assume.

Safe travels!

 

Thanks to both of you for your complete and thoughtful responses. Some great information to follow up on. We made it home (and went over another high Sierra pass) without incident. Love this ride!

 

Sounds great!
I've taken my '22 350h down to Florida a couple of times through the high elevations of West Virginia, 2700+ miles round trip. Loaded to the gills with my lovely wife's essentials on board. Very impressed, very comfortable seats, never skipped a beat.

 

Brakes on these cars(i got hybrid) are disaster.after two heavy breaking stopping power was very weak and the smell was awful also

 

Typical brake pad materials for everyday drivers are usually formulated for longevity. One good long emergency stop and you'll need to tread carefully for a bit as the pads cool down. These are nowhere near racing performance pads and rotors that can take repeated heavy braking like ceramic(rotors) ceramic(pads) systems. Hybrid's use their motor generators to stop primarily with the pads stepping in around 5mph to 0. The pads will be used in extreme circumstances like emergency braking and repeated heavy use.

 

If you are not using your brakes and got a sulfur smell, its probably the catalytic converter over worked from climbing the hill.