2020 Discovery HSE - Cranks But Won't Start

ClearTheCode admin answer: When an engine cranks but doesn't start, it typically indicates a problem with one of the three essentials for combustion: fuel, air, or spark (or sometimes compression, but that's less common for a sudden no-start). Given your strong cranking, the battery is likely fine.

Here's a diagnostic approach:

1. Check for Fuel Delivery:
   • Listen for Fuel Pump: Turn the ignition to the 'ON' position (don't crank) and listen for a faint hum from the rear of the vehicle. This is the fuel pump priming. If you don't hear it, check the fuel pump fuse and relay.
   • Fuel Pressure: A more advanced check involves testing fuel pressure at the rail, but this requires specialized tools.
2. Check for Spark: This is harder without a spark tester, but you can try pulling a spark plug, reconnecting it to its coil, grounding the plug, and having someone briefly crank the engine to see if it sparks (be cautious).
3. Immobilizer System: A fault in the immobilizer system (e.g., a bad key, faulty antenna, or module) can prevent the engine from starting. Look for a security light on the dash that stays on or flashes rapidly when trying to start.
4. Crankshaft Position Sensor: A failing crankshaft position sensor can prevent the PCM from knowing when to fire the injectors and spark plugs, leading to a crank-no-start condition. This often won't throw a code until after multiple failed start attempts.

When to see a shop:

• If you're unable to confirm fuel delivery or spark.
• If there's an immobilizer fault, as these often require dealer-level diagnostics and programming.
• If you suspect a sensor failure (like the crankshaft position sensor), as proper diagnosis usually involves a scan tool to read live data and potential fault codes (even pending ones).