Engine Speed – What is an acceptable engine speed after a preselect or grade braking downshift?
A. The TCM is programmed to command downshifts only when the resulting increase in engine speed will not exceed factory-set limits. Specifically: For the LB7 and LLY diesel engines: Maximum engine speed immediately following a preselect or grade braking downshift can be as high as 4,000 RPM. After a grade braking downshift, if vehicle speed continues to increase, an upshift will occur at 4,800 RPM engine speed. For the L18 gas engine: Maximum engine speed immediately following a preselect or grade braking downshift can be as high as 4,650 RPM. After a grade braking downshift, if vehicle speed continues to increase, an upshift will occur at 5,000 RPM engine speed.
Related Questions
- Engine Speed - If I have manually preselected a lower range resulting in a downshift, but the vehicle is allowed to continue to accelerate, will the transmission upshift?
- Engine Speed - What is an acceptable engine speed after a preselect or grade braking downshift?
- Automatic Grade Braking - Downshifts - To which gear will it downshift in each mode?
