- Cruise control
- Fast idle control
- Idle speed control
- PTO operation
- Vehicle speed limiting
- Speedometer
- Progressive shift
- Idle shutdown
- Operation of the air inlet heater
- Secure idle theft deterrent
- Trip data
- Maintenance data
There are three different methods that can be used to obtain the information for the ECM to use for calculating vehicle speed. The ECM can calculate vehicle speed by either of the following means:
- The ECM monitors the signal from a vehicle speed sensor in pulses per kilometer (mile). The vehicle speed sensor is connected to the vehicle speed input circuit (terminals 32 and 33 of the ECM). This is the "Vehicle Speed Calibration" option.
- The ECM receives a message over the J1939 data link from the transmission ECU that indicates revolutions per kilometer (mile) of the transmission output shaft. This is the "Vehicle Speed Cal (J1939-Trans)" option.
- The ECM receives a message over the J1939 data link from the Anti-lock Brake System (ABS) that contains information about the wheel speed. This is the "Vehicle Speed Cal (J1939-ABS)" option.
Each of these methods require a specific calibration number to be programmed into the ECM to calculate vehicle speed.
For the "Vehicle Speed Calibration" option that uses the vehicle speed sensor, the ECM must know the number of pulses that are produced by the vehicle speed sensor during each kilometer (mile) of travel by the vehicle. In order to find the number of pulses that are produced by the sensor, multiply the tire size by the axle ratio. Multiply the number that was obtained in the previous calculation by the number of teeth on the output shaft that is used by the sensor to obtain the pulses.
For the "Vehicle Speed Cal (J1939-Trans)" option, the ECM must know the number of times that the output shaft revolves per kilometer (mile) of travel by the vehicle. This can be calculated by one of the following methods:
- Divide the pulses per kilometer (mile) of the sensor on the transmission output shaft by the number of teeth on the transmission output shaft.
- Multiply the axle ratio by the number of revolutions per kilometer (mile) of the tire.
For the "Vehicle Speed Cal (J1939-ABS)" option, the ECM must know a calibration number. The number is calculated by dividing the actual tire revolutions per kilometer (mile) by the tire revolutions per kilometer (mile) that is programmed into the ABS.
The ECM calculates vehicle speed by converting the vehicle speed signal to kilometers per hour (km/h) or to miles per hour (mph). The conversion factor is customer programmable and the conversion factor is stored in pulses per km (PPKM) or pulses per mile (PPM).
The variable for the tire revolution could be affected by changing from bias ply tires to radial tires and vice versa. Also, changing to radial tires that have a low profile could affect the variable for the tire revolution. This result may change the actual vehicle speed which could result in performance complaints or in complaints about fuel consumption. If the configuration of the tire has been changed, determine the new variable for the tire revolution. Enter the new value in pulses per km (PPKM) or in pulses per mile (PPM). The preferred method is obtaining the data from the individual tire manufacturers for the specific tire that is being used.
Note: The ECM speedometer signal is set to 18,600 pulses per km (PPKM) or to 30,000 pulses per mile (PPM). For "GM Truck Manufacturer" configurations, the output of the speedometer is set to
- Use Caterpillar Electronic Technician (ET) to Determine the Configuration for the Vehicle Speed Input to the ECM.
- Establish communication between the Caterpillar Electronic Technician (ET) and the ECM.
- Access the "Configuration Parameter List". View the "Vehicle Speed Parameters". Determine if the vehicle is configured to use the "Vehicle Speed Calibration" option, the "Vehicle Speed Cal (J1939-Trans)" option, or the "Vehicle Speed Cal (J1939-ABS)" option.
Proceed to Test Step 2 if the vehicle is configured to use the "Vehicle Speed Calibration" option.
Proceed to Test Step 3 if the vehicle is configured to use the "Vehicle Speed Cal (J1939-Trans)" option.
Proceed to Test Step 4 if the vehicle is configured to use the "Vehicle Speed Cal (J1939-ABS)" option.
- Calculate Pulses Per Kilometer (Mile) When All of The Variables Are Known.
- Calculate pulses per kilometer (PPKM) or pulses per mile (PPM) according to the following formula:
PPKM = K x Ra x N.
PPM = M x Ra x N.
PPKM - This symbol represents the number of pulses per kilometer.
PPM - This symbol represents the number of pulses per mile.
K - This symbol represents the tire revolutions per kilometer. This is a constant that is divided by the tire static loaded radius.
M - This symbol represents the tire revolutions per mile. This is a constant that is divided by the tire static loaded radius.
Ra - This symbol represents the rear axle ratio. The rear axle ratio can typically be found on the housing of the rear axle, or the rear axle ratio can typically be found on the specification sheet for the vehicle.
N - This symbol represents the number of chopper teeth on the transmission drive shaft. The magnetic pickup sensor is mounted here. The number of chopper teeth is usually 16. Some transmissions have 11 tooth chopper wheels.
- Use Cat ET to enter pulses per km (PPKM) or pulses per mile (PPM) into the ECM.
- Calculate pulses per kilometer (PPKM) or pulses per mile (PPM) according to the following formula:
- Calculate the Revolutions Per Kilometer (Mile) of The Transmission Output Shaft.
- The correct revolutions per kilometer (mile) of the transmission output shaft must be entered for the "Vehicle Speed Cal J1939-Trans" setting. If this value is unknown, either of the following calculations can be used to obtain the correct setting:
- Divide the pulses per kilometer (mile) of the sensor on the transmission output shaft by the number of teeth on the transmission output shaft.
- Multiply the axle ratio by the number of revolutions per kilometer (mile) of the tire.
- Use Cat ET to enter the calculated value into the ECM.
- The correct revolutions per kilometer (mile) of the transmission output shaft must be entered for the "Vehicle Speed Cal J1939-Trans" setting. If this value is unknown, either of the following calculations can be used to obtain the correct setting:
- Calculate Tire Revolutions Per Kilometer (Mile) When All of The Variables are Known.
- The correct calibration number must be entered for the "Vehicle Speed Cal J1939-ABS" setting. If this value is unknown, the following calculation can be used to obtain the correct setting:
Divide the actual tire revolutions per kilometer (mile) by the tire revolutions per kilometer (mile) that is broadcast by the ABS.
For example, the actual tire revolutions per kilometer (mile) could equal 400 revolutions per kilometer (mile). The tire revolutions per kilometer (mile) that is broadcast by the ABS could equal 500 revolutions per kilometer (mile).
The formula would be 400 / 500 = 0.800.
Therefore, 0.800 would be the value that would be entered into the ECM.
- Use Cat ET to enter the calculated value into the ECM.
- The correct calibration number must be entered for the "Vehicle Speed Cal J1939-ABS" setting. If this value is unknown, the following calculation can be used to obtain the correct setting: