GMC Sierra 1500 Ambient Air Temperature Sensor: A Guide for 1999-2008 Models
Is your truck's outside temperature display wrong or is your automatic A/C acting up? Your ambient air temperature sensor is the likely cause.
- A bad sensor will cause an incorrect outside temperature display and can disable your automatic A/C.
- This is a very easy and quick part to replace yourself, usually located behind the grille.
- Always check the electrical connector for corrosion before replacing the sensor, as this is a common point of failure.
- It's normal for the temperature to read high at startup due to engine heat; it will correct itself after a few minutes of driving.
What the Ambient Air Temperature Sensor Does on Your Sierra
Think of the ambient air temperature sensor as your truck's personal thermometer. It's a small electronic part, called a thermistor, that changes its electrical resistance as the outside air temperature changes. The truck's main computer reads this signal to operate the outside temperature display and the automatic climate control system. When it fails, the computer gets bad information, which can cause several noticeable problems.
Common Symptoms of a Failing Sensor
A bad ambient air temperature sensor is not a critical failure, but it can be annoying. Here are the most common signs that yours needs to be replaced:
- Incorrect Temperature Display: The temperature shown on your dash or overhead console will be obviously wrong. It might be stuck on a very low number (like -40°F), a high number, or show dashes.
- Automatic A/C Malfunction: If you use the "Auto" setting for your climate control, a bad sensor can prevent it from working correctly. The A/C might not blow cold air on a hot day because the truck thinks it's already cold outside.
- Check Engine Light: A failed sensor can trigger a Check Engine Light. You may see diagnostic trouble codes (DTCs) such as P0071, P0072, or P0073 when you scan the vehicle.
A Note on "Heat Soak"
It is normal for the temperature to read higher than the actual outside temp right after you start your truck, especially if it was parked in the sun or recently driven. The sensor is located near the radiator and gets warm from the engine's heat. After driving for a few minutes, the airflow will cool the sensor and it will begin to show the correct temperature. This is not a sign of a bad sensor.
Choosing the Right Aftermarket Sensor
For a simple part like this, an aftermarket sensor is a perfectly good choice. However, quality can vary between brands. It is also worth noting that the genuine GM part (ACDelco) is often priced competitively with higher-end aftermarket options.
- Professional Grade (Higher Tier): Brands like Standard Ignition (SMP) are often considered a top-tier aftermarket choice. They focus on meeting or exceeding original equipment (OE) specifications and are a common choice for professional repair shops.
- Standard Replacement (Value Tier): Brands like Dorman and Walker Products offer a direct replacement at a lower cost. Dorman is known for making a huge variety of parts and often redesigns components to fix original flaws, though online reviews from mechanics can be mixed regarding long-term durability. For a simple sensor, they are generally a reliable and budget-friendly option.
Check the Connector First!
Before you buy a new sensor, inspect the old one. The sensor lives at the front of the truck and is exposed to rain, snow, and road salt. Over time, the electrical connector and wiring can get corroded or damaged, causing the same symptoms as a failed sensor. If the connector pins are green with corrosion, cleaning it or replacing the connector pigtail might fix your problem without needing a new sensor.
Cost of Replacing the Ambient Air Temperature Sensor
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket Sensor | $9.91 - $72.04 |
| New OEM (ACDelco) Sensor | $15 - $40 |
| Shop Labor | $50 - $100 |
Frequently Asked Questions
Where is the sensor located on my 1999-2008 Sierra?
The sensor is located at the front of the truck, typically mounted on the radiator core support, behind the grille. You can usually see it by looking through the grille openings.
Is this an easy part to replace myself?
Yes, this is a very easy DIY job. In most cases, the sensor is held in by a simple clip or a single small bolt. You just unplug the electrical connector, remove the old sensor, install the new one, and plug it back in. The entire job usually takes less than 15 minutes.
Can a bad temp sensor really make my A/C stop working?
Yes. On trucks with automatic climate control, the system relies on the ambient sensor's reading to decide when to engage the A/C compressor. If the sensor is telling the computer that it's -20°F outside, the system will not turn on the A/C, even if it's 90°F in the cabin.
Do I need to reset the computer after replacing the sensor?
Generally, no. Once the new sensor is installed, the system should start reading the correct temperature after a short drive. If you had a Check Engine Light, you may need to clear the code with an OBD2 scanner, but it will often clear itself after a few drive cycles.
Technical Specifications
OEM Part Numbers: 15047946 25775833 15029274
Typically a two-terminal thermistor sensor that plugs into a wiring harness behind the front grille.
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The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
- GMC Sierra 1500: