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

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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.