* Park Pawl Failure: This is the most common cause. The park pawl is a small mechanism that physically locks the output shaft of the transmission, preventing it from rotating. Wear, damage, or a broken spring can prevent it from engaging properly. This is a significant internal transmission problem that requires repair or replacement of the transmission.
* Park/Neutral Safety Switch Failure: This switch prevents the vehicle from starting unless the gear selector is in Park or Neutral. If it's faulty, it might not be sending the correct signal to the system, allowing the transmission to move even if the shifter is in Park. This is a less expensive and easier repair than a park pawl issue.
* Shift Linkage Problems: The linkage connecting the shifter to the transmission can become bent, worn, or disconnected. This could lead to the transmission not being properly placed in Park, even if the shifter shows it's in Park. Inspection of the linkage is key here.
* Transmission Control Module (TCM) Issue (less likely): While less frequent in this older model, a malfunctioning TCM (the computer that controls the transmission) could theoretically cause this, though it's less probable than mechanical failures. Diagnosis would require specialized tools.
* Damaged Shift Cable: The cable connecting the shifter to the transmission can be damaged or stretched, preventing the proper engagement of the park pawl.
Important Safety Note: Driving a vehicle with this problem is extremely dangerous. The truck could roll unexpectedly, causing an accident. Do *not* drive the truck until the issue is diagnosed and repaired by a qualified mechanic. Have it towed.
To diagnose the problem, a mechanic will likely:
1. Inspect the shift linkage visually: Check for bends, breaks, or loose connections.
2. Test the park/neutral safety switch: This involves using a multimeter to test its electrical continuity.
3. Perform a road test (with caution, preferably on a flat, safe area): While dangerous, this can help determine if the problem is consistent or intermittent.
4. Inspect the transmission internally (if other checks fail): This requires removing the transmission and often complete disassembly for a thorough inspection of the park pawl and other internal components.
The cost of repair can vary significantly depending on the cause. A faulty safety switch is relatively inexpensive to fix, while a damaged park pawl usually requires a transmission rebuild or replacement, which can be quite costly.
