* Neutral Safety Switch (NSS) Failure: This is the most likely culprit. The NSS is a crucial safety device that prevents the engine from starting unless the transmission is in Park or Neutral. A faulty NSS might not be registering the Park position correctly, thus preventing the starter from engaging. The crackling noise could be the starter motor struggling to engage due to the partially functioning switch.
* Faulty Starter Motor: While the starter *does* engage in Neutral, the added load of the engine trying to turn over in Park (with greater resistance) might reveal a weakness in the starter motor itself. The crackling sound could be the motor's brushes or solenoid struggling. A failing starter often makes clicking or grinding noises.
* Low Battery Voltage: Though you mentioned it started in Neutral, a weak battery might have enough power to crank in a less demanding position (Neutral), but not enough to overcome the increased resistance of the engine and transmission in Park.
* Faulty Ignition Switch: A problem within the ignition switch itself could be preventing the proper signal to reach the starter when in Park. This is less likely if it starts in Neutral.
* Wiring Issues: Damaged or corroded wiring in the circuit between the NSS, ignition switch, and starter motor could interrupt the signal or power flow necessary to start in Park.
* Transmission Problems (Less Likely): While less probable, a problem within the transmission that interferes with the proper Park position engagement could indirectly affect the NSS signal. This is less likely given the Neutral start.
Troubleshooting Steps:
1. Check the battery voltage: Make sure the battery is adequately charged. A low voltage can cause intermittent starting issues.
2. Inspect the NSS: Locate the NSS (usually on the transmission) and visually inspect it for any obvious damage. You may need to test it with a multimeter to confirm its functionality.
3. Listen carefully to the sounds: Pay close attention to the sounds you hear when trying to start in Park. A distinct clicking suggests a problem with the starter solenoid, while grinding indicates internal problems within the starter motor.
4. Check the wiring: Examine all wiring related to the starting system for any signs of damage, corrosion, or loose connections.
5. Professional Inspection: If you can't identify the problem yourself, take your Cavalier to a qualified mechanic for diagnosis and repair. They have the tools and experience to properly diagnose the issue.
The crackling noise in Neutral suggests the problem isn't completely unrelated to the starter itself. It might be worth starting with the battery voltage check, followed by a detailed examination of the NSS and its wiring. A faulty NSS is often the simplest and cheapest fix, but if not, more in-depth diagnosis is required.
