Home · 2021 Mercedes-benz S-class Phev · Complaints

What 33 owners told NHTSA about the 2021 Mercedes-benz S-class Phev

These are the actual owner complaints behind this car’s reliability verdict, filed with the federal government, unedited. They’re unverified reports, not confirmed defects: read them as leads for your pre-purchase inspection, not a diagnosis.

All (33)Crash / fire / injury (4)Electrical system (10)Wheels (6)Driver assistance (5)Engine & cooling (5)Brakes (3)Engine (3)Lane Departure (3)Speed control (3)Communication (2)Fuel system (2)

3 of 33 complaints match · Speed control · clear filters

Jan 27, 2022Electrical systemSpeed controlEngine

Background: This is a V-8, gas vehicle.The 12-volt battery gives CRITICAL CHARGE notifications constantly. Incident: Dry pavement, 400-mile, January winter night, highway driving in Wisconsin Northwoods at posted 70 mph; some with cruise control, some without cruise control. Seat belt was in use. On four occasions, car independently, without any warning, dropped from 70 mph to 35 mph, projecting me forward. No reduction in speed signage No small town drive through. With car and semi-truck traffic behind me, luckily no rear end collisions, injury or death occurred. During dealership repair service 12/09/2021 - 12/17/2021, along with mailed pending recall from manufacturer for ENGINE CONTROL SOFTWARE UPDATE, was told December 28, 2021 it would occur. When car returned for service on 01/18/2022 (and is still in for service today - 01/26/2022), I was told 01/14/2022 was the update release. I have not received any updated manufacturer notifications. Dealership (Illinois) says CONTROL MODULE on order from West Coast. (Photo - Portion of text response from Dealership Service Writer on 01/26/2022 is attached.) Dangerous vehicle. This newly designed model has engineering problems. Should not have been released to sales market. Numerous ELECTRICAL Problems have occurred since my August 5, 2021 purchase.

NHTSA ODI 11449057

Nov 29, 2021Speed controlTransmission & drivetrainCrash1 injury

The contact owns a 2021 Mercedes-Benz S580. The contact stated while driving at 60 MPH, the contact pressed a button on the steering wheel to engage the cruise control function on the vehicle. The contact stated when driving past a mileage sign stating 40 MPH, the vehicle suddenly reduce in speed to 40 MPH, while the contact was on the highway in the fast lane. The contact was able to move the vehicle over to the side of the road waited a few minutes took off the cruise control function and reapplied it back on and continued to drive the vehicle again. After a few minutes when the contact was exiting off the highway and the contact drove past a sign that said 60 MPH when suddenly the vehicle automatically accelerated on its own which caused the contact to rear-end a parked vehicle in front of them. The air bags did not deploy or the S.O.S. signal did not turn on. The contact was injured where they broke two bones in the right foot, left knee injury, and whiplash on their neck due to the seat belt. There was medical treatment at the scene. A police report was filed. The vehicle was towed to a local dealer where the vehicle was inspected but could not diagnose the caused the failure. The vehicle was not repaired. The manufacturer was made of the failure. The failure mileage was approximately 976.

NHTSA ODI 11442018

Jul 26, 2021Speed controlLane Departure1 injury1 death

UNKNOWN

NHTSA ODI 11426542

Working with the data? Download all 33 complaints as CSV · fetched from NHTSA July 20, 2026

How to use these: a complaint is one owner’s report, filed voluntarily and published unverified. Patterns matter more than any single story. If several owners describe the same failure at similar mileage, put that system at the top of your pre-purchase inspection list. Back to the full 2021 Mercedes-benz S-class Phev verdict →