Car won't start? Start with the symptom, not the part.
Before buying a starter, battery, fuel pump, or another expensive guess, determine what the vehicle is actually doing. This flowchart walks through the basic diagnostic path for a vehicle that either won't crank or cranks but won't start.
START WITH WHAT THE CAR IS ACTUALLY DOING
A vehicle that “won't start” can have very different problems. Before replacing anything, pay attention to what happens when you turn the key or press the start button.
ENGINE DOESN'T CRANK
If the engine doesn't turn over at all, start with the starting and electrical system.
Check the battery state of charge, battery terminals and cables, grounds, fuses and relays, and the starter circuit. A single click, rapid clicking, complete silence, or very slow cranking can each point the diagnosis in a different direction.
Don't assume a starter is bad just because the engine won't crank. A weak battery, poor cable connection, bad ground, starter relay, park/neutral switch, clutch switch, wiring problem, or security system can produce similar symptoms.
ENGINE CRANKS BUT WON'T START
If the starter is turning the engine normally but the engine won't run, the starting system has already done its job.
Now you're looking for the things an engine needs to run: fuel, ignition, air, compression, and correct timing.
Check for spark. Verify fuel delivery. Look for obvious air-intake problems. A scan tool can also provide valuable clues from stored trouble codes and live data.
The goal isn't to immediately identify the failed part. The goal is to determine which system isn't doing its job, then narrow the problem from there.
TOOLS COMMONLY USED FOR NO-START DIAGNOSIS
You don't need every diagnostic tool ever made to begin troubleshooting. A few basic tools can answer a surprising number of questions:
- Digital multimeter for battery voltage, power, ground and electrical testing
- Test light for quick power and circuit checks
- Spark tester for checking ignition output safely
- Fuel-pressure gauge for verifying fuel-system pressure
- Noid light for checking injector control signals
- Scan tool for diagnostic trouble codes and vehicle data
- Compression tester when a mechanical problem is suspected
- Basic hand tools for access, connections and component inspection
DON'T FORGET THE SIMPLE STUFF
Before diving deeply into diagnostics, think about what happened immediately before the problem started.
Was the battery recently disconnected? Was something repaired? Did the vehicle sit for weeks? Is the security light flashing? Did the problem begin immediately after fueling, maintenance, extreme weather, or electrical work?
A loose connector from yesterday's repair can save you from spending three hours diagnosing tomorrow's imaginary fuel-pump failure.
ONE TEST AT A TIME
Good troubleshooting is a process of eliminating possibilities.
Observe the symptom. Test the system. Follow the evidence.
Avoid replacing parts simply because they're commonly associated with a particular symptom. Confirm what you can before spending money.
That's the difference between diagnosing a problem and shopping for guesses.
SAFETY NOTE
Automotive electrical, fuel and ignition systems can involve high current, high voltage, moving components, hot surfaces and flammable fuel. Use appropriate test equipment, follow the vehicle manufacturer's service information, and don't perform a procedure you're not comfortable doing safely.
Vehicle designs vary considerably, so this guide is intended as a general troubleshooting starting point, not a replacement for model-specific service information.
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