2020 Forester Cranks But Won't Start

ClearTheCode admin answer:

A 'cranks but no start' condition on your 2020 Subaru Forester Premium can be frustrating, especially when it was running fine previously. This usually points to a lack of one of the three essentials for combustion: spark, fuel, or compression. Since it's cranking strongly, we can likely rule out a completely dead battery or starter motor.

Here's a systematic approach to diagnose the issue:

1. Check for Fuel Delivery:
   • Listen for Fuel Pump: Turn the key to the 'ON' position (without cranking) and listen for a faint hum from the rear of the vehicle for a few seconds. This indicates the fuel pump is priming.
   • Fuel Pressure: If you have a fuel pressure gauge, check the pressure at the fuel rail. Low or no pressure indicates a fuel pump, fuel filter, or fuel line issue.
   • Action: If no hum, check the fuel pump fuse and relay. If they're good, the pump itself might be faulty.
2. Check for Spark:
   • Spark Plugs/Coils: A lack of spark can prevent starting. While harder to check without tools, a failing crankshaft position sensor or camshaft position sensor can prevent spark.
   • Action: If you have a spark tester, pull a spark plug wire (if accessible) and test for spark. If not, consider if any recent work might have disturbed ignition components.
3. Check for Air (and Sensors):
   • Air Intake: Ensure the air intake isn't blocked. While less common for a sudden no-start, it's a quick check.
   • MAF Sensor: A completely failed Mass Air Flow (MAF) sensor can sometimes prevent starting, though it usually throws a code.
4. Immobilizer System:
   • Security Light: Check if the security light on your dashboard is flashing or staying on solid when you try to start. A fault in the immobilizer system (key not recognized) will prevent the engine from firing.
   • Action: Try your spare key to rule out a faulty transponder chip in your primary key.
5. OBD-II Scan: Even without a Check Engine Light, pending or stored codes might exist. Hook up your scanner to check for any codes, especially related to engine sensors (crankshaft, camshaft, MAF).

When to see a shop: If you've confirmed fuel pump operation and spark, and the immobilizer light isn't indicating an issue, it's best to have your Forester towed to a professional mechanic or Subaru dealership. Diagnosing sensor failures, complex electrical issues, or internal engine problems (like timing belt/chain issues, though less likely for a sudden no-start on a 2020 model) requires specialized diagnostic equipment and expertise.