Transmission Related:
* Low Transmission Fluid: This is the most common and easiest to check first. Low fluid can cause all sorts of shifting problems, from harsh shifts to complete failure to shift. Check your fluid level (consult your owner's manual for location and proper level) and the condition of the fluid (it should be red and clean, not brown or burnt smelling). Low fluid often indicates a leak somewhere in the system that needs attention.
* Faulty Transmission Solenoids or Valves: These electrical components control fluid flow within the transmission. A malfunctioning solenoid can prevent the transmission from shifting correctly. Diagnosis usually requires a scan tool to check for error codes.
* Worn Clutch Packs or Bands: These are internal components that wear out over time. Worn clutches or bands can cause slipping, difficulty shifting, or inability to shift at all. This is a major repair.
* Internal Transmission Problems: More serious issues like broken gears, damaged planetary gears, or other internal failures require a complete transmission overhaul or replacement.
* Transmission Linkage Problems (Manual): If it's a manual transmission, problems with the linkage (cables or rods) connecting the shifter to the transmission itself can prevent shifting. This includes bent, broken, or disconnected components.
Other Potential Causes:
* Shift Cable Adjustment (Automatic): While less common, an improperly adjusted shift cable can interfere with gear selection in an automatic transmission.
* Faulty Neutral Safety Switch: This switch prevents the car from starting unless the gear selector is in Park or Neutral. A faulty switch could prevent shifting or starting.
* Electrical Problems: Problems with the car's electrical system, such as a blown fuse or a faulty wiring harness, could affect the transmission's operation. Check all relevant fuses.
* Computer Issues (PCM/TCM): The Powertrain Control Module (PCM) or Transmission Control Module (TCM) controls the transmission's operation. A malfunctioning computer can cause various shifting problems. A scan tool is needed for diagnosis.
Troubleshooting Steps:
1. Check the transmission fluid level and condition. This is the easiest and most important first step.
2. Check fuses related to the transmission. Consult your owner's manual.
3. Have the car scanned for diagnostic trouble codes (DTCs). This will provide clues as to the cause of the problem. An OBD-II scanner is needed.
4. Inspect the transmission linkage (if manual). Look for bent, broken, or disconnected components.
Important Note: If you are not comfortable working on your car yourself, take it to a qualified mechanic for diagnosis and repair. Transmission problems can be complex and costly to fix. Ignoring the issue can lead to further damage and more expensive repairs down the road.
