* Thickened Transmission Fluid: This is the most common culprit. As the temperature drops, transmission fluid thickens significantly. If the fluid is already old or low quality, the increased viscosity makes it difficult for the pump to circulate it properly, preventing the transmission from engaging gears. This is exacerbated if the fluid is contaminated with debris.
* Fluid Leaks: A leak, even a small one, can lead to low fluid levels. Low fluid levels make the problem of thickened fluid even worse. Check for leaks around the transmission pan, lines, and seals.
* Transmission Filter Clogged: A dirty or clogged transmission filter restricts fluid flow, contributing to the shifting problem when the fluid is thick.
* Internal Transmission Problems: While less likely to be solely temperature-dependent, problems with the transmission's internal components (valves, solenoids, clutches) can worsen in cold weather. Worn parts may not function correctly with the thicker fluid. This could be a more serious and expensive repair.
* Low Battery Voltage: While less directly related, a weak battery can provide insufficient power to the transmission's solenoids, which control shifting. This is more likely to manifest as sluggish shifting or problems with other electrical components in the vehicle.
* Shift Linkage (Manual Transmission): If it's a manual transmission (unlikely in a Venture, but possible), frozen linkage could prevent shifting.
Troubleshooting Steps:
1. Check the Transmission Fluid: This is the first and most important step. Check the fluid level with the engine running and warmed up (if possible). Note the color and smell. Dark, burnt-smelling fluid indicates it needs changing. If the level is low, you have a leak and that needs addressing immediately.
2. Change the Transmission Fluid and Filter: If the fluid is old, dark, or low, a change is essential. This often resolves the problem.
3. Check for Leaks: Carefully inspect the transmission and surrounding areas for any signs of fluid leakage.
4. Battery Check: Test the battery's voltage to ensure it's supplying sufficient power.
5. Professional Diagnosis: If the problem persists after checking the fluid and for leaks, take it to a qualified mechanic for a proper diagnosis. They have tools and expertise to check for internal transmission problems.
It's crucial to address this issue promptly. Driving with a transmission problem can cause further damage and lead to costly repairs.
