Simple/Easy Checks (Do these first!):
* Throttle Cable: A sticking or broken throttle cable can prevent the transmission from receiving the signal to downshift. Check for free movement and proper connection.
* TV Cable (Throttle Valve Cable): This cable (if equipped) regulates shift points based on throttle position. A misadjusted or damaged TV cable is a common cause of shifting problems. Improper adjustment can lead to late or no downshifts.
* Fluid Level: Low transmission fluid is a major cause of shifting problems. Check the fluid level while the engine is running and warm (consult your owner's manual for the proper procedure). Also inspect the fluid for color and smell; burnt smelling fluid indicates significant internal problems.
* Kickdown Switch: The kickdown switch (usually located on the throttle body) signals the transmission to downshift when the accelerator is fully depressed. A faulty switch can prevent downshifts.
More Complex Issues (Require Professional Diagnosis):
* Transmission Solenoids: These electrically controlled valves within the transmission regulate fluid flow to control shifting. A faulty solenoid can prevent downshifts, or cause erratic shifting.
* Governor: This component regulates shift points based on vehicle speed. A malfunctioning governor can prevent downshifts, especially at higher speeds.
* Transmission Valve Body: This contains the hydraulic system that controls shifting. Worn or damaged valve body components can cause a variety of shifting issues.
* Torque Converter: A faulty torque converter can prevent smooth power transfer, leading to hesitation and lack of downshifts.
* Low or Dirty Transmission Filter: A clogged filter restricts fluid flow, impacting shifting performance.
* Internal Transmission Problems: Severe wear and tear on the internal components of the transmission (e.g., clutch packs, bands) can cause a complete failure to downshift. This often presents as a general lack of power and shifting issues.
* Computer/PCM Issues: The Powertrain Control Module (PCM) controls the transmission. A faulty PCM can lead to various transmission problems, including the failure to downshift. This is less likely, but possible.
Troubleshooting Steps:
1. Start with the simple checks: Fluid level, throttle and TV cables (if applicable), and kickdown switch.
2. Check for diagnostic trouble codes (DTCs): Use an OBD-II scanner to read any codes stored in the PCM. These codes can point to the source of the problem.
3. Professional Diagnosis: If the simple checks don't reveal the problem, take your van to a qualified transmission specialist or mechanic. They have the tools and expertise to diagnose more complex issues.
Ignoring transmission problems can lead to catastrophic failure, resulting in costly repairs. Address the issue promptly.
