The exact cause could be several things, including:
* Transmission fluid level and condition: Low or contaminated transmission fluid is a very common culprit. Check the fluid level (with the engine running and warm) and its condition (color, smell, presence of metal particles). Low fluid can cause overheating and damage.
* Transmission speed sensor: This sensor provides crucial information to the transmission's computer. A faulty sensor can lead to erratic shifting and the blinking OD light.
* Transmission solenoid or valve body issues: Internal problems within the transmission's valve body or solenoids can also trigger the light. These components control fluid flow within the transmission.
* Wiring problems: Damaged or corroded wiring between the transmission, the sensor(s), and the control module can disrupt communication and cause the blinking light.
* Transmission control module (TCM) failure: In rarer cases, the TCM itself might be malfunctioning.
You should not continue driving the van with a continuously blinking OD light. Continued use can cause further damage to the transmission. You'll likely need to have it professionally diagnosed by a mechanic specializing in transmissions or a Ford dealership. They will use a diagnostic scanner to pinpoint the exact problem. Ignoring this warning could lead to a costly transmission repair or replacement.
