* Low or Dirty Transmission Fluid: This is the easiest and cheapest thing to check first. Low fluid can cause all sorts of transmission problems, including inability to shift into drive. Dirty fluid can cause sticking valves and other internal issues. Check the fluid level (with the engine running and the transmission warmed up) and the condition (it should be reddish-pink, not brown or black). If it's low or dirty, a fluid change and filter replacement are crucial.
* Transmission Internal Problems: This is the more likely and costly scenario. Several internal components could be failing, including:
* Forward clutches: These are responsible for engaging the forward gears. If they're worn, burned, or broken, you won't be able to go into drive.
* Shifting mechanism: The internal parts that control gear selection might be malfunctioning, preventing the transmission from engaging the forward gears.
* Valve body problems: The valve body controls fluid flow within the transmission. A problem here can lead to shifting issues.
* Torque converter: This component transfers power from the engine to the transmission. A faulty torque converter can prevent forward motion.
* Shift Linkage/Cable Issues: While less likely, problems with the linkage or cable that connects the shifter to the transmission could be at fault. This could be a broken cable, bent linkage, or a problem with the shifter itself. Inspect for any visible damage or unusual play in the linkage.
* Solenoids: These electrically controlled valves regulate fluid flow within the transmission. A faulty solenoid can prevent gear engagement.
* Computer/Sensor Issues: Though less common, a malfunctioning transmission control module (TCM) or a faulty speed sensor could interfere with the transmission's ability to shift into drive.
What to do:
1. Check the Transmission Fluid: This is the absolute first step. Do not skip this.
2. Consult a Repair Manual: A repair manual specific to your 1996 Mercury Grand Marquis will provide diagrams and troubleshooting steps.
3. Professional Diagnosis: Unless you have significant experience with automatic transmissions, you'll likely need a professional mechanic to diagnose the problem accurately. They have the tools and expertise to properly test the transmission fluid, pressure, and electrical components. A simple visual inspection might not reveal the cause.
Don't try to drive the car extensively with this problem, as you could cause further damage to the transmission. Towing it to a mechanic is recommended.
