2018 Cadillac XT5: check engine light

Filed May 26, 2026 · Engine, Steering · MI

Check engine light sensor came on in mid-May which is the result of a faulty thermostat, also triggering a "Steering Assist is Reduced" message on the dashboard which I consider to be a safety issue. This is a known and common problem for this make, year and model and the cost to fix the problem is very expensive. This issue has been reported by many Cadillac owners on their forum. My mechanic confirmed the problem with the thermostat caused the steering assist is reduced message, along with the air conditioning malfunctioning.

Filed Jan 23, 2026 · Engine, Steering · MI

To Whom It May Concern,I am writing to formally report a safety concern involving my 2018 Cadillac XT5, VIN [XXX] . Recently, my vehicle displayed a “Steering Assist Reduced” message on the dashboard while driving. This warning significantly increases the physical effort required to steer the vehicle, especially at low speeds, and I believe it presents a genuine safety hazard.Upon taking the vehicle to an authorized Cadillac dealership, I was informed that the vehicle had stored diagnostic trouble code P0128 (Engine Coolant Temperature Below Thermostat Regulating Temperature). The dealer explained that a malfunctioning thermostat caused the steering assist reduction message to appear. However, at no point did the vehicle illuminate a Check Engine Light, despite the presence of an emissions‑related fault code.I am concerned for several reasons:A critical engine fault (P0128) did not trigger a Check Engine Light, leaving me unaware of any underlying issue. The vehicle reduced power steering assist as a result of an unrelated thermostat malfunction, creating a sudden and unexpected increase in steering effort. This behavior poses a safety risk, particularly in situations requiring quick steering response or low‑speed maneuvering.Cadillac has issued Service Bulletin 17NA158, which acknowledges that thermostat or coolant‑temperature‑related issues can trigger steering assist warnings. This suggests the manufacturer is aware of the problem, yet no recall or corrective action has been issued.Given that steering assist reduction directly affects vehicle control, I believe this issue warrants investigation. A driver should not lose steering assist because of a thermostat fault, nor should a vehicle fail to illuminate a Check Engine Light when a diagnostic code is present.I respectfully request that the federal safety agency review this matter to determine whether a safety‑related defect exists in the 2018 Cadillac XT5 and similar GM vehicles. Sumitting this for my mother. INFORMATION REDACTED PURSUANT TO THE FREEDOM OF INFORMATION ACT (FOI

Filed Mar 25, 2025 · Engine · 86,000 miles · NJ

The contact owns a 2018 Cadillac XT5. The contact stated that while driving at an undisclosed speed, the vehicle stalled with the check engine warning light illuminated. The vehicle was towed to the dealer where it was diagnosed that the engine had failed and needed to be replaced. The vehicle was not repaired. The manufacturer was not made aware of the failure. The approximate failure mileage was 86,000.

Filed Sep 20, 2024 · Engine, Transmission · NJ

The coolant thermostat was broken and gave two check engine codes P0128 and P0128P. AC was not functioning when the thermostat was not working, which can be dangerous in summer. It is also a very common problem with Cadillac XT5 and GMC Acadia.

Filed Apr 26, 2024 · Transmission · MD

Check engine light (power reduced steering drive safely) notice came on. Code reads P0128, coolant below thermostat regulating temperature. This is an on going issue with Cadillac. It’s definitely a defect because if you go on YouTube you will see it’s not just my vehicle even on low miles vehicles. Then you are left with no choice but to get repaired at the dealer only to be ripped off. 180 for diagnostic testing at dealer to find out this is an ongoing issue across the US

Filed Jul 31, 2023 · Engine · PA

When driving the car on Jul 20, the check engine light came on. It went off upon arriving home. We had it checked at our local NAPA Auto Care and they did an Electronic Engine Control Test. The garage did not clear Trouble Codes and advised us to take the car to a dealer. Upon driving the car on Jul 30, the check engine light came on once again. In May 2020, when we had our car in for service, at Sutliff, in State College, PA, they took care of the Engine Control, software issue. This dealer is no longer open so we started taking our car to Blaise Alexander in Altoona, PA We, also, have had several incidents with the Parking Brake not releasing. We took the car to Blaise Alexander, in Altoona, on 3-14-23, and they said that the software showed no problem with the Parking Brake. They advised me to call a tow truck and have it towed into their garage the next time it happened. There is a Cadillac Dealer in Ebensburg, PA which is approx 30 miles away. We are in a dilemma as to have it towed there or have it towed to the GM Dealer in Altoona, PA which is approx 16 miles away. Our car has 50, 813 miles on it. I will have it towed either to the Cadillac dealer or the GM dealer.

Filed May 26, 2022 · Body, Electrical · MI · fire

Driving down the road and my 2018 Cadillac XT5 started on fire for no reason and no engine lights came on. I loss all driving control power steering in the matter of seconds and was trapped in the car waiting for cars to clear so I can run out. The car is with my insurance company the car is now a total loss and I don't think they will investigate. I called GM to make a complaint. The fireman said he had just put a fire out on the same car a week ago. I found out that we have 2 more cars in the Macomb county MI area that caught on fire in the last 3 months same type of car.