* Transmission Problems: This is the most likely culprit. Problems within the automatic transmission itself could include:
* Low transmission fluid: Check the fluid level and condition. Low fluid or fluid that's burnt, dark, or smells burnt indicates serious problems.
* Faulty valve body: This controls the shifting process. A malfunctioning valve body can prevent proper shifting.
* Worn clutch packs or bands: These components wear over time and can cause slipping or inability to shift.
* Damaged or malfunctioning governor: The governor regulates shift points based on vehicle speed. A faulty governor will lead to incorrect shifting.
* Internal transmission damage: More serious internal problems like broken parts or damaged planetary gears can prevent shifting.
* Stuck or broken shift linkage: Though less common, a mechanical issue in the linkage could prevent the transmission from selecting higher gears.
* Electrical Problems: The transmission's control system relies on electrical components:
* Transmission control module (TCM) issues: The TCM is the "brain" of the transmission. A faulty TCM can cause various shifting problems.
* Wiring harness problems: Damaged or corroded wires can interrupt signals to and from the TCM and transmission.
* Speed sensor issues: The transmission relies on speed sensors to determine when to shift. A malfunctioning sensor will result in improper shifting.
* Other Potential Issues (Less Likely):
* Vacuum leaks: Although less common with electronically controlled transmissions, vacuum leaks can sometimes affect shifting in older vehicles.
Troubleshooting Steps:
1. Check the transmission fluid: This is the *first* thing to do. Low or contaminated fluid is a major problem.
2. Have the transmission fluid and filter changed (if the fluid is dirty): A simple fluid change might resolve minor issues.
3. Check for any diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any codes stored in the car's computer. These codes can point to specific problems.
4. Consult a repair manual specific to your 1991 Chrysler Imperial: Repair manuals provide detailed diagrams and troubleshooting steps.
5. Take it to a qualified mechanic: If you're not comfortable working on the transmission yourself, take it to a transmission specialist or a reputable mechanic. They have the tools and expertise to diagnose and repair the problem accurately.
It's crucial to address this issue promptly. Continuing to drive with the car stuck in low gear will likely cause further damage to the transmission.
