P0118 OBD2 Fault Code in 2003 Chevrolet Trailblazer: AC On Causes Engine Death - Sensor or System Issue?
I initially received a P0118 fault code on my 2003 Chevrolet Trailblazer, but the engine temperature was stable for several weeks, which led me to rule out a thermostat issue. After resetting the code, P0118 reappeared. The problem is now that when I turn on the air conditioning, the vehicle stalls while idling. I'm wondering whether this points to a faulty ECT (Engine Coolant Temperature) sensor or if it's something else entirely. Given that the repair involves removing the wheel and alternator—estimated at $300 labor—I'd like to know if replacing just the sensor is sufficient, or if I should replace both the thermostat and ECT sensor. Additionally, I've noticed that while the AC function works, the blower fan does not operate for either heating or cooling. All fuses are confirmed good, and no diagnostic codes appear on my OBD-II scanner. Is a 'through scan' required, and if so—is it possible to perform this at home with an OBD-II device, or do I need to visit a professional shop?
As summer approaches, safety is key. Replace both the thermostat and ECT sensor using the correct temperature rating—your vehicle is likely draining coolant due to this issue. A fresh coolant flush will also help. If the engine dies when AC is turned on, it may indicate underlying fault codes (such as manufacturer-specific P0999 or higher), or a failing AC compressor (possibly seized or overcharged). An in-depth diagnostic scan is recommended. Without air conditioning, summer driving becomes impractical.