Description:
This parameter must be programmed when a Two Speed Axle On/Off Switch is used by the ECM in order to adjust the vehicle speed calibration. When a two speed axle is used, the change in gear ratios from the high speed range to the low speed range alters the calibration of the Vehicle Speed Limit and Vehicle Speed Calibration, which require a calibration adjustment to ensure the ECM-driven speedometer and ECM stored information correctly reflect the actual vehicle speed.
Available:
All electronically controlled on-highway engines covered in this handbook
Range:
Advantages:
Proper calculation of the Low Speed Range Axle Ratio and High Speed Range Axle Ratio parameters is essential for proper cruise control and speedometer (if controlled by the ECM) operation, and accurate fleet and driver trip data.
Disadvantages:
None
Recommendations:
Let the OEM calculate the Low Speed Range Axle Ratio and High Speed Range Axle Ratio parameters based on the truck specifications.
Recalculate and program the Low Speed Range Axle Ratio and High Speed Range Axle Ratio parameters if any changes are made to the rear axle ratios. Note that repairing or replacing the rearend with the same axle ratio will not cause a problem or require any recalculation for this parameter.