* Transmission Issues: This is a strong possibility. A failing torque converter, low transmission fluid, problems with the transmission valve body, or a worn-out transmission itself could all cause this. The engine may be running fine, but the transmission isn't receiving the necessary power or isn't engaging properly.
* Engine Problems: While less likely given the timing (stalling *after* putting it in gear), a weak engine could struggle to handle the load of the transmission engaging. This might be due to issues with:
* Fuel System: A clogged fuel filter, failing fuel pump, or issues with fuel injectors could starve the engine of fuel, causing a stall under load.
* Ignition System: Problems with the spark plugs, ignition coil, or distributor (if applicable) could prevent the engine from combusting the fuel properly.
* Air Intake System: A severely restricted air filter or other intake problems could limit the engine's ability to breathe.
* Sensors: Various sensors monitor engine and transmission operation. A faulty sensor, such as a crankshaft position sensor, throttle position sensor, mass airflow sensor, or others, can send incorrect information to the engine control module (ECM), leading to stalling.
* Vacuum Leaks: A leak in the intake manifold or vacuum lines can cause erratic engine operation and stalling, especially under load.
* Alternator/Battery: Though less common as the immediate cause, a failing alternator or weak battery might not provide enough power to run the engine under the added strain of engaging the transmission. This is more likely to manifest as slow cranking or dimming lights, but a severely deficient charging system could be a factor.
* Throttle Body: A dirty or malfunctioning throttle body can lead to inconsistent fuel delivery.
What to do:
1. Check your fluids: Start by checking your transmission fluid level. Low fluid is a significant cause of transmission problems. Also check your engine oil level.
2. Have it diagnosed professionally: The best approach is to take your Trailblazer to a qualified mechanic for a proper diagnosis. They have the tools and expertise to accurately pinpoint the issue, saving you time, money, and potential further damage. Simply describing the symptoms to them will help them focus their diagnostic efforts.
Don't attempt extensive repairs yourself unless you have significant mechanical experience. Improper repairs can worsen the problem.
