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Vehicle Speed Parameters
Vehicle Speed Calibration
OEM
Description:
The value ( Pulses per Mile, PPM) of this parameter is
used by the ECM to convert the vehicle speed signal
into miles per hour (or kilometers per hour). The value is
calculated using tire revolutions per mile, rear axle ratio
and the number of teeth on the transmission chopper
wheel. This parameter is programmed by the OEM.
PPM = M x Ra x N
Example: 31,200 = 502 x 3.90 x 16
M = Tire revolutions per mile. This information is
available from the tire manufacturer.
R
a
= Rear Axle Ratio. This is typically found
on the housing of the rear axle, or on the
specifi cation sheet for the vehicle
N = Number of chopper teeth on the transmission
drive shaft where the magnetic pickup is
mounted. The value is typically 16, but may be
11.
Available:
All electronically controlled on-highway engines
Range:
Engine
Range
Cat
Default
Minimum Maximum
3126E, C9
GM
4000 PPM
(2485 ppkm)
384000 PPM
(238080 ppkm)
32000 PPM
(19884 ppkm)
3126E, C7, C9
OTHER
4000 PPM
(2485 ppkm)
384000 PPM
(238080 ppkm)
Not
Programmed
C-10, C-12,
C-15, C-16
4000 PPM
(2485 ppkm)
150000 PPM
(93226 ppkm)
14000 PPM
(8696 ppkm)
C11, C13, C15
& All EPA07
4000 PPM
(2485 ppkm)
150000 PPM
(93226 ppkm)
Not
Programmed
Advantages:
Proper calculation of the Vehicle Speed Calibration
parameter is essential for proper cruise control and
speedometer (if controlled by the ECM) operation, and
accurate Fleet and Driver Trip Data.
Disadvantages:
Miscalculation of the Vehicle Speed Calibration
parameter will cause all values calculated by the ECM
using the Vehicle Speed value to be in error (e.g. vehicle
miles, fuel economy, etc.). Precise calculation is critical
to provide accurate calculated values from the ECM.