* Crankshaft Position Sensor (CKP Sensor): This sensor tells the engine's computer where the crankshaft is in its rotation. If it's failing, especially in cold temperatures where the oil is thicker, it may not provide a reliable signal, causing the engine to shut down. Cold temperatures can exacerbate existing problems in this sensor.
* Camshaft Position Sensor (CMP Sensor): Similar to the CKP sensor, a faulty CMP sensor won't accurately tell the computer where the camshaft is, leading to misfiring and stalling, particularly during the initial cold start when the system needs precise timing.
* Fuel Pump: A weak fuel pump might struggle to deliver enough fuel, especially when the fuel is cold and thicker. The added stress of a cold start might be enough to cause it to fail temporarily or completely. You might also hear a weaker-than-usual "whine" from the pump during the key-on-before-crank stage.
* Fuel Filter: A clogged fuel filter can restrict fuel flow, leading to similar issues as a weak fuel pump, especially during cold starts.
* Throttle Body: Ice formation in the throttle body is less likely in warmer climates but possible. This can restrict airflow, leading to stalling.
* Mass Airflow Sensor (MAF Sensor): A faulty MAF sensor provides inaccurate readings of the incoming air. This can cause poor fuel mixture calculations and stalling, especially during cold starts when the engine needs a specific fuel/air ratio.
* Battery: A weak or failing battery might not provide enough power for the starter and other components during a cold start, causing the engine to crank slowly or not at all, effectively quitting almost immediately. Test the battery's voltage and cranking amps.
* Ignition System (Coil Packs, Spark Plugs, Wires): While less likely to cause an immediate stall, issues with the ignition system are more prone to problems in the cold. Weak spark from worn plugs or failing coils would be exacerbated by cold weather's effects on oil viscosity and component responsiveness.
Troubleshooting Steps:
1. Check the battery: This is the easiest and cheapest check. A simple voltage test with a multimeter will show if it's low.
2. Listen for unusual noises: Pay close attention to any sounds during cranking. A weak fuel pump might whine, and a clicking sound might indicate a starter problem (although less likely to cause immediate shutdown).
3. Check engine codes: Use an OBD-II scanner to read any diagnostic trouble codes (DTCs) stored in the car's computer. These codes can often pinpoint the problem.
4. Professional Diagnosis: If you can't identify the problem yourself, take it to a qualified mechanic, especially one familiar with Subarus. They'll have the tools and expertise to diagnose the issue accurately.
It's crucial to address this problem promptly as continued attempts to start the engine with a faulty component can cause further damage.
