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Test Step 2. Calculate the Revolutions Per Kilometer (Mile) of the Transmission Output Shaft

 

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Vehicle Speed Circuit - Calibrate
Up
TM-9-2320-312-24-2 Truck Tractor Yard Type: 46 662 GVWR DED 4x2 M878A2 Manual
Next
Test Step 4. Inspect the Speedometer Calibration
428
TM 9-2320-312-24-2
Troubleshooting Section
Test Step 2. Calculate the Revolutions
The tire revolution variable could be affected by
Per Kilometer (Mile) of the Transmission
changing from bias ply tires to radial tires, and
Output Shaft
vice versa. Also, changing to low profile radial
tires could affect the tire revolution variable. This
result may change the actual vehicle speed which
A. The correct revolutions per kilometer (mile) of
could result in performance complaints or fuel
the transmission output shaft must be entered
consumption complaints. If the tire configuration has
for the "Vehicle Speed Cal J1939-Trans" setting.
been changed, determine the new tire revolution
If this value is unknown, either of the following
variable. Enter the new value in pulses per km
calculations can be used to obtain the correct
(PPKM) or pulses per mile (PPM). The preferred
setting:
method is obtaining the data from the individual
tire manufacturers for the specific tire that is being
Divide the pulses per kilometer (mile) of the
used.
sensor on the transmission output shaft by the
number of teeth on the transmission output
Note: The ECM speedometer signal is set to 18,600
shaft.
pulses per km (PPKM) or 30,000 pulses per mile
(PPM). For "GM Truck Manufacturer" configurations
Multiply the axle ratio by the number of
with SEP00 or newer software, the output of the
revolutions per kilometer (mile) of the tire.
speedometer is set to 2,485 PPKM (4,000 ppm).
This setting cannot be changed. All speedometers
B. Program the calculated value into the ECM.
that are driven by the ECM output (J1/P1 terminal
36 and terminal 37) must match the fixed output of
Expected Result:
the ECM for proper operation.
The value is within the valid range of the ECM.
Test Step 1. Determine if the ECM
Receives the Vehicle Speed Input
Results:
from the "Vehicle Speed Calibration"
Option or from the "Vehicle Speed Cal
Yes Once the value is entered, verify that the
(J1939-Trans)" Option.
ECM is accurately measuring vehicle speed.
Proceed to Test Step 4.
A. Connect Caterpillar Electronic Technician (ET) to
No Recalculate the value and re-enter the
the cab data link connector. If the software for
correct value into the ECM. STOP.
the ECM is older than SEP00, proceed to Test
Step 3.
Test Step 3. Calculating Pulses Per
Kilometer (Mile) When all the Variables
B. If SEP00 or newer software is used in the ECM,
are Known.
access the "Configuration Parameter List". View
the "Vehicle Speed Input" parameter. Determine
A. Calculate pulses per kilometer (PPKM) or pulses
if the vehicle is configured to use the "Vehicle
per mile (PPM).
Speed Calibration" option, "J1/P1:32&33" or the
"Vehicle Speed Cal (J1939-Trans)" option.
PPKM = K Ra N.
Expected Result:
PPM = M Ra N.
The ECM is using software that is dated prior to
K This symbol represents the tire revolutions
SEP00 or the ECM is configured to use the "Vehicle
per kilometer. This is a constant that is divided
Speed Calibration" option.
by the tire static loaded radius.
Results:
M This symbol represents the tire revolutions
per mile. This is a constant that is divided by the
Yes Proceed to Test Step 3.
tire static loaded radius.
No The ECM is configured to use the "Vehicle
Ra This symbol represents the rear axle ratio.
Speed Cal (J1939-Trans)" option. Proceed to Test
The rear axle ratio can typically be found on the
Step 2.
housing of the rear axle, or the rear axle ratio
can typically be found on the specification sheet
for the vehicle.

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