Vacuum modulator
The vacuum modulator is a device that controls the amount of vacuum applied to the transmission's shift valve. If the vacuum modulator is faulty, it can cause the transmission to lock up in manual low.
Governor
The governor is a device that measures the vehicle's speed and sends a signal to the transmission's control unit. If the governor is faulty, it can cause the transmission to lock up in manual low.
Shift linkage
The shift linkage is the mechanism that connects the shift lever to the transmission. If the shift linkage is loose or out of adjustment, it can cause the transmission to lock up in manual low.
Transmission fluid
If the transmission fluid is low or dirty, it can cause the transmission to lock up in manual low.
To diagnose the problem, you will need to check the vacuum modulator, governor, shift linkage, and transmission fluid. If you are not comfortable doing this yourself, you should take your vehicle to a qualified mechanic.
Here are some additional tips that may help you resolve this issue:
Make sure that the transmission is in the correct gear. If the transmission is not in manual low, it will not lock up.
Check the vacuum lines to the vacuum modulator. Make sure that the lines are not cracked or leaking.
Check the governor for damage. The governor is located on the back of the transmission.
Check the shift linkage for looseness or damage.
Check the transmission fluid level. The fluid should be between the "Full" and "Add" marks on the dipstick.
If you are still experiencing problems, you should take your vehicle to a qualified mechanic.
