What would cause a Subaru Impreza to not start?
When a Subaru Impreza won’t start, the cause is most often electrical, ignition, or fuel related rather than a seized engine. Common culprits include a dead battery, a faulty starter, ignition or immobilizer issues, or a problem with fuel delivery.
Starting problems can stem from a wide range of factors, depending on the model year and engine type. This guide details the most frequent causes, how they present, and practical steps to diagnose them, from quick checks you can perform at home to when professional help is warranted.
Common causes a Subaru Impreza may not start
Below is a concise overview of the categories most often responsible for a no-start condition. The items are arranged from the most common to less frequent but still plausible during a no-start scenario.
- Dead or severely discharged battery
- Faulty or failing alternator not charging the battery while the engine is cranking
- Failing starter motor or solenoid
- Worn or failing ignition switch or ignition cylinder
- Ignition system issues causing no spark (bad spark plugs, ignition coils, or wiring)
- Fuel delivery problems (empty fuel tank, failed fuel pump, clogged fuel filter, or failing fuel pressure)
- Fuel pump relay or main EFI/relay failure
- Sensor or control module problems (crankshaft position sensor, camshaft position sensor, or other critical engine sensors)
- Immobilizer/security system not recognizing the key or an anti-theft fault
- Electrical fuses or relays blown or faulty (including the main fuse or ignition relay)
- Electrical grounding issues or damaged wiring harnesses
- Engine mechanical problems (timing belt/chain issue, blown head gasket, or severe loss of compression)
- Vehicle in a no-start condition due to transmission-related safety features (manual clutch switch or similar)
In addition to these, some model-year specifics apply. For example, immobilizer or anti-theft warnings are common indicators of a security system problem, while a no-start with a flashing security light on the dashboard often points to the key fob or immobilizer.
Diagnosing a no-start: practical steps
These diagnostic steps help isolate the cause. Start with the simplest checks and progress to more advanced tests as needed.
- Check the battery: verify you have at least about 12.6 volts with the engine off; if significantly lower, charge or replace the battery. Inspect for corrosion on terminals and ensure the negative ground strap is secure.
- Listen for signs when turning the key: a single loud click or a rapid clicking sound can indicate a weak battery, bad ground, or a failing starter or relay.
- Observe dashboard lights and security indicators: if the immobilizer or security light stays on or flashes in a pattern, the key may not be recognized and the car may not start.
- Check for cranking behavior: if the engine turns over slowly, the battery or starter is suspect; if the engine does not turn at all, focus on power supply, ignition, and starter circuits.
- Inspect fuses and relays: look for blown fuses (EFI, main fuse) and check the starter relay and other relevant relays; replace as needed.
- Test for fuel delivery: ensure there is fuel in the tank and listen for the fuel pump priming when turning the key to ON. If you don’t hear it, the fuel pump, relay, or wiring could be at fault.
- Check for spark: use a spark tester or remove a spark plug to verify if ignition is delivering a spark to each cylinder during cranking.
- Scan for trouble codes: connect an OBD-II scanner to read any codes (for example, P030x misfire codes, P0520 battery/charging issues, or P0685 ECM power input codes) and use the data to pinpoint faulty systems.
- Evaluate mechanical condition: if you suspect timing belt/chain slip or a major compression loss, that requires professional testing (compression test/ leak-down test) and is not a DIY quick check.
These steps form a practical workflow to identify the most likely cause without specialized tools. If the no-start persists after these checks, a professional diagnosis is advised to avoid misdiagnosis or unintended damage.
When to seek professional help
Consult a technician if you experience persistent no-start symptoms after performing basic battery, ignition, and fuel checks, or if you encounter warning lights such as the immobilizer, check engine, or battery/charging icons during diagnosis. Complex issues like ECU faults, immobilizer integration problems, or timing concerns typically require professional diagnosis and specialized equipment.
Model-specific notes
Subaru Impreza models can present particular no-start signals that help narrow down the cause. For instance, a flashing security light usually signals a problem with the key fob or immobilizer system, while a no-start with a strong battery and a single click often points toward the starter or ignition switch. Clues from the owner’s manual and service bulletins for your specific year and engine (for example 2.0L or 2.5L variants) can provide targeted guidance.
Summary
A Subaru Impreza that won’t start is most often related to power, ignition, fuel delivery, or security systems. Start with the basics—battery health, terminal connections, and whether the starter engages—then move to fuel delivery and spark checks, and finally scan for trouble codes. If in doubt, or if the immobilizer light is involved, seek professional help to avoid misdiagnosis and potential damage.
