* Crankshaft Position Sensor (CKP): This sensor tells the computer the engine's rotational position. A faulty CKP sensor will prevent the engine from starting, even if the fuel pump is working. This is a very common cause of no-start issues.
* Cam Position Sensor (CMP): Similar to the CKP sensor, the CMP sensor tells the computer the camshaft's position. A malfunctioning CMP sensor can also prevent starting.
* Ignition System: This includes the ignition coil(s), spark plugs, and ignition module. A problem in any of these components could prevent the spark needed to ignite the fuel-air mixture. Worn spark plugs are a common suspect.
* Security System: Your Explorer might have a Passive Anti-Theft System (PATS). If the system doesn't recognize the key, it will prevent the engine from starting. Try a different key if you have one.
* Battery: Even if the fuel pump primes (which uses relatively little power), a weak battery might not provide enough power to crank the engine over. Have the battery tested. A low voltage reading even if the car seems to turn over a bit, could be the culprit.
* Starter Motor: The starter motor is responsible for cranking the engine. A faulty starter won't engage, even if the battery is good. You'll often hear a clicking sound if the starter is the problem.
* Neutral Safety Switch: The automatic transmission needs to be in Park or Neutral for the car to start. Make sure the shifter is securely in one of these positions.
* Low Fuel: Although less likely since the pump is priming, exceptionally low fuel can sometimes interfere with the system.
Troubleshooting Steps:
1. Check the Battery: Have it load tested at an auto parts store. A weak battery can appear fine at first glance.
2. Listen Carefully: When you turn the key, do you hear *any* cranking sound from the engine? If not, the problem is likely with the battery, starter, or neutral safety switch. If you hear clicking, the battery or starter is suspect.
3. Check for Codes: Use an OBD-II scanner to check for diagnostic trouble codes (DTCs). These codes can pinpoint the problem area. Auto parts stores often loan these out for free.
4. Visual Inspection: Look for any loose or corroded connections on the battery terminals, starter, and other ignition components.
5. Start with the Easy Stuff: Make sure the car is in Park (automatic) or Neutral (manual). Try a different key, if available.
If you're not comfortable working on your car yourself, take it to a mechanic for diagnosis and repair. Describing the symptoms precisely (fuel pump primes, no cranking/no start, etc.) will help them narrow down the cause quickly.
