* Crank Position Sensor (CPS): This sensor tells the computer the engine's rotational position. A faulty CPS prevents the engine from receiving the signal to fire the spark plugs, resulting in a no-start condition even though the engine cranks. This is a very common culprit in no-start situations.
* Cam Position Sensor (CMP): Similar to the CPS, but for the camshaft. A faulty CMP will also prevent the engine from firing.
* Ignition Coil(s) or Spark Plugs: These are responsible for igniting the air/fuel mixture. A weak or faulty coil(s) or worn spark plugs will prevent combustion. Check for spark at the plugs.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor can provide incorrect readings, leading to a lean or rich fuel mixture that prevents starting.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position. A faulty TPS can cause incorrect fuel delivery and prevent starting.
* Fuel Injectors: While the fuel pump is running, the injectors may be clogged or faulty, preventing fuel from being sprayed into the cylinders.
* Security System: The car's anti-theft system might be preventing the engine from starting. Check for any flashing lights or unusual behavior related to the alarm system.
* Low Compression: While less likely if the car ran fine recently, low compression in one or more cylinders would prevent a start. This would require a compression test.
Troubleshooting Steps:
1. Check for spark: Use a spark tester or carefully hold a grounded spark plug wire near the engine block (be cautious!) while cranking the engine to see if there's spark. If not, focus on the ignition coil(s), CPS, and CMP.
2. Check fuel pressure: Even though the pump runs, verify the fuel pressure at the fuel rail meets specifications (check your car's repair manual). Low pressure points to a problem in the fuel system beyond the pump and filter.
3. Check codes: Use an OBD-II scanner to retrieve any diagnostic trouble codes (DTCs) stored in the car's computer. These codes can pinpoint the problem area.
4. Inspect wiring and connections: Look for any damaged, loose, or corroded wires or connectors, especially those related to the sensors and ignition system.
5. Test sensors: If you have a multimeter, you can test the voltage and resistance of the CPS, CMP, MAF, and TPS to see if they're within specifications. This typically requires a repair manual for accurate testing procedures.
If you're not comfortable performing these checks, it's best to take the car to a qualified mechanic for diagnosis and repair. Trying to guess without proper tools and knowledge can lead to further damage or wasted time and money.
