Why is my Subaru turning on but not starting?
It’s usually caused by fuel delivery problems, ignition faults, or a security/immobilizer issue that prevents the engine from firing. This guide outlines the most common causes and practical steps you can take to diagnose the problem.
Security and immobilizer issues
Many no-start situations in Subarus trace to the vehicle’s anti-theft system or key recognition problems. If the immobilizer won’t acknowledge the key, the engine may crank but fail to start. Here are typical signs and quick checks.
- The security/immobilizer light behaves oddly or stays on/off in an unusual pattern.
- Using a spare key or re-synchronizing the key fob temporarily resolves the issue, if only briefly.
- You may need dealer or locksmith assistance to reprogram or re-sync the key if the system won’t recognize it.
Concluding: If the immobilizer is at fault, the symptom is often a no-start with security indicator activity. Professional service or key reprogramming is often required to restore normal starting.
Fuel delivery problems
Without adequate fuel reaching the cylinders, the engine may turn over but not catch. Common culprits include an empty tank, a failing fuel pump, or a clogged fuel filter.
- Low or empty fuel can mimic a starting failure even if the fuel gauge seems misleading.
- A weak or failing fuel pump may not provide enough pressure to start the engine.
- Blown fuses or a faulty fuel pump relay can interrupt fuel delivery to the rails.
- A clogged or old fuel filter can restrict flow and prevent starting.
Concluding: If you suspect fuel delivery is the culprit, listen for the fuel pump priming when you turn the key to ON and check relevant fuses/relays as a starting point.
Ignition system faults
Issues with sparks or timing can prevent combustion even when the engine turns over. Symptoms often point to wear or failure in ignition components or timing sensors.
- Worn or fouled spark plugs can fail to ignite the air-fuel mixture reliably.
- Failed ignition coils or damaged spark plug wiring can produce weak or no spark.
- Crankshaft position sensor (CPS) or camshaft position sensor (CMP) faults can prevent proper engine timing and startup.
- A faulty engine control module (ECU) configuration or sensor data can misfire or prevent starting.
Concluding: Ignition issues often require inspecting spark quality, coil health, and key timing sensors, with scanning for fault codes to pinpoint the faulty component.
Sensor and ECU faults
Modern Subarus rely on multiple sensors to determine when and how to start. Failures here can stop the engine from starting even if other systems look nominal.
- Crankshaft position sensor or camshaft position sensor failures disrupt timing data needed for ignition and fuel injection.
- Mass air flow (MAF) sensor or manifold absolute pressure (MAP) sensor problems can misread air intake and stall startup attempts.
- ECU/PCM faults or corrupted software can prevent proper engine control and starting sequences.
Concluding: Sensor or ECU faults are often diagnosed with an onboard scanner and may require replacing a sensor or reflashing/updating the ECU software.
Electrical issues and fuses
A car’s electrical health underpins starting performance. Loose connections, corroded terminals, or blown fuses can interrupt critical circuits.
- Weak or dead battery, or loose battery terminals, can prevent the engine from starting even if the accessories power up.
- Blown EFI/injection fuses, ignition fuses, or a faulty ground strap can interrupt essential circuits.
- Alternator issues can lead to insufficient charging, causing the battery to dip during a start attempt.
Concluding: Start with a battery voltage check and inspect all visible electrical connections and fuses related to the starting and fuel systems.
Mechanical timing or compression issues
Less common but critical, mechanical problems can leave a Subaru unable to start because the engine cannot properly compress or time the spark and fuel delivery.
- Timing belt/chain failure or backlash can prevent proper valve timing and combustion.
- Severe engine wear or dropped compression in one or more cylinders can stop an engine from starting.
Concluding: Mechanical problems usually require a professional assessment, including compression tests and, if needed, timing system inspection or replacement.
Diagnostic steps you can take
To narrow down the issue without jumping straight to a house call, use these practical checks. They help distinguish between fuel, ignition, and sensor/electrical problems.
- Check the battery and cables. Ensure the battery reads about 12.6 volts with the engine off and higher when cranking. Inspect for corrosion and secure connections.
- Listen for fuel pump priming. When turning the key to ON, you should hear a brief pump hum or whir from the rear of the car. If you don’t, inspect the fuel pump fuse/relay and the pump itself.
- Scan for trouble codes with an OBD-II scanner. Codes related to CPS, CMP, MAF, or fuel delivery can guide you to the faulty system.
- Check for spark, if safe to do so. A diagnostic spark test can reveal ignition issues; if no spark appears, inspect ignition coils and related wiring.
- Check fuel pressure if possible. A gauge reading within spec confirms fuel delivery; a low reading points to pump, relay, or filter issues.
- Inspect immobilizer/key function. Try a spare key and observe the security indicator. If the immobilizer light remains active or you can’t start with any key, plan for dealer or locksmith assistance.
Concluding: If the no-start persists after these checks, a dealer or qualified technician with Subaru-specific diagnostic tools should perform a deeper inspection, as the issue could involve the ECU, immobilizer, or a failing component beyond basic home testing.
Summary
In Subaru no-start scenarios, the most common culprits are fuel delivery problems, ignition or spark faults, and immobilizer/security issues, followed by sensor/ECU and electrical faults. Begin with basic checks—battery, fuses, and whether the fuel pump primes—then use an OBD-II scan to guide you. If uncertainty remains or the problem involves security systems or engine timing, seek professional diagnosis to avoid further damage or misdiagnosis.
Why does my Subaru car turn on but won't start?
Electrical system issues, such as blown fuses, corroded battery terminals, or damaged wiring, can also prevent a Subaru car from starting. It's essential to inspect the electrical system components and connections for signs of damage or corrosion and address any issues promptly.
How do I know if my Subaru starter is bad?
How to Tell the Signs of a Broken Subaru Starter
- Slow or No Cranking. One of the primary signs of a broken starter motor in a Subaru is slow or no cranking when you turn the key in the ignition.
- Clicking Noise.
- Grinding Sound.
- Frequent Stalling.
- Smoke or Burning Smell.
How do you force restart a Subaru?
Press and Hold the Power Button: Press and hold the power button for approximately 10-15 seconds until the screen goes blank and the system powers off. Wait a Few Moments: Allow the system to remain powered off for a few moments before pressing the power button again to restart it.
What does it mean when my car will turn on but not start?
A car that turns on but won't start likely has a problem with the fuel, spark, or air system, or a faulty starter, even if the battery has power. Common issues include a clogged fuel filter, bad spark plugs, or a failing fuel pump. Less common but still possible causes include electrical problems like a faulty ignition switch or immobilizer.
You can watch this video to learn about the common problems and things to check when your car won't start: 1mBudget MechanicYouTube · Dec 8, 2023
Fuel and air issues
- Empty fuel tank: Check the fuel gauge, and consider that parking on a hill can sometimes prevent a car with low fuel from starting, says this YouTube video.
- Clogged fuel filter: A dirty filter can block fuel from reaching the engine.
- Faulty fuel pump: If the pump isn't working, it can't send fuel to the engine. You may hear a clicking sound from the fuel pump relay, but the pump itself could still be bad.
- Bad spark plugs: Worn-out spark plugs can't ignite the fuel properly.
Electrical and starter issues
- Weak or dead battery: Even though the lights turn on, the starter motor requires more power to crank the engine than the lights or radio do, says this YouTube video.
- Faulty starter motor or solenoid: A clicking sound when you turn the key often points to a bad starter or starter solenoid.
- Bad alternator: The alternator charges the battery while the car runs. If it's not working, the battery will eventually lose its charge, leading to a no-start condition even if it seems fine at first.
- Faulty ignition switch: The switch that turns the car on may be broken.
- Blown fuse or relay: A blown fuse or a bad relay in the fuel or ignition system can prevent the car from starting.
Other possibilities
- Bad timing belt or low engine compression: These can prevent the engine from running correctly even if it turns over.
- Immobilizer issue: The car's anti-theft system may be preventing it from starting.
What to do
- Check the obvious first: Make sure the car is in Park or Neutral, and try moving the steering wheel slightly if it's locked.
- Inspect the battery: Check the battery terminals for corrosion and make sure they are tight. If the car starts after cleaning and tightening them, or with a jump start, the battery is likely the issue.
- Listen for sounds: A rapid clicking sound often indicates a weak battery, while a single click could mean a bad starter solenoid. A whirring sound could point to a failing fuel pump.
- Consult a mechanic: Some issues, like a bad fuel pump, ignition switch, or timing belt, require professional diagnosis and repair.
