Car Won't Start? Diagnostic Checklist
Systematic Diagnosis: Why Won't My Car Start?
A no-start condition has three possible root causes: no spark, no fuel, or no compression. This checklist helps you narrow it down without expensive shop visits.
Step 1: What Happens When You Turn the Key?
| Symptom | Most Likely Cause | Fix |
|---|---|---|
| Nothing at all — no lights, no sound | Dead battery or loose connection | Check battery terminals, jump start |
| Clicks but won't crank | Weak battery or bad starter | Try jump start; if it clicks fast = battery, single click = starter |
| Cranks normally but won't fire | Fuel or ignition problem | Continue to Step 2 |
| Cranks slowly | Dying battery or corroded terminals | Clean terminals, test/replace battery |
Step 2: Check for Spark
Remove a spark plug, reconnect it to the wire, ground the plug against the engine block, and have someone crank the engine. You should see a bright blue spark. No spark? Check ignition coils, crankshaft position sensor, and fuses.
Step 3: Check for Fuel
Turn the key to ON (not start). Listen for the fuel pump — you should hear a 2-second whirring sound from the rear of the car. No sound? Check the fuel pump fuse and relay first.
Step 4: Check for Error Codes
Even if the car won't start, an OBD2 scanner can often still read codes with the ignition in the ON position. Common no-start codes include P0335 (crankshaft sensor), P0230 (fuel pump), and P0340 (camshaft sensor).
When to Call a Tow Truck
- Smoke or burning smell from the engine bay
- Fluid leaking under the car
- You've tried the above steps and can't isolate the cause
- The car started briefly then died — could be a fuel pump or immobilizer issue