Why does the Buick ambient temperature always display -40 degrees?

[FinleyRose]

When the Buick's ambient temperature consistently displays -40 degrees, it indicates a malfunction in the outdoor temperature sensor, which needs to be replaced promptly. Function and principle of the ambient temperature sensor: Its role is to monitor the ambient temperature and control the operation of the air conditioning system. The working principle involves a bimetallic strip inside the sensor, which has different thermal expansion coefficients. This allows the strip to deform when reaching a certain critical temperature range, causing the contacts to connect and complete the electrical circuit. Method for replacing the ambient temperature sensor: Before replacement, first disconnect the negative terminal of the battery. Locate the sensor in front of the radiator, replace it with a new one, and then reconnect the battery.

[VanNorah]

Last time when I was driving my Buick Regal, I encountered the same issue - the ambient temperature on the dashboard kept showing -40 degrees, and the automatic AC mode stopped working properly. This problem is usually caused by a faulty small temperature sensor located near the front radiator grille, which is responsible for detecting outside temperature. Either the sensor got clogged with mud and failed, or rodents chewed through the wiring. When I lifted the car later, I found the sensor connector had indeed come loose. While this minor issue doesn't affect driving, it prevents the automatic AC from intelligently cooling or heating, making summer drives particularly uncomfortable. I recommend checking the sensor connector and wiring as soon as possible - replacing it with an OEM sensor only costs about 200-300 yuan.

[HazelRose]

My old Buick Excelle XT had the same issue recently. In the middle of summer, it showed -40 degrees, and no matter how I adjusted the AC, only hot air came out. A common problem with Buicks is that the ambient temperature sensor at the front is prone to failure. The sensor is located behind the bumper, and even a small stone kicked up from the road can damage it. I replaced the sensor myself: first removed the lower front bumper cover, found a coin-sized plastic sensor, unplugged it, and installed the new one—took just three minutes. If replacing it doesn’t fix the issue, you’ll need to check if the wiring has been damaged by engine bay heat. Buying the part yourself costs around 70-80 RMB, saving over 400 in labor fees!

[LeMax]

The core issue of abnormal ambient temperature display is a fault in the temperature detection circuit. Buick vehicles generally use negative temperature coefficient thermistors for ambient temperature sensors, where resistance changes reflect temperature values. When the signal line is short-circuited to ground, the instrument receives a 0V signal, and the vehicle preset corresponds 0V to -40°C. Troubleshooting involves three steps: disconnect the sensor connector and measure resistance (approximately 2.1 kΩ at room temperature); check the harness-to-ground resistance (should be infinite); finally, inspect the signal voltage at the instrument end (should be 5V when the sensor is disconnected). In most cases, connector corrosion causes the short circuit, so special attention should be paid to waterproofing the front bumper connector during the rainy season.