Vehicle Speed Circuit

427

TM 9-2320-312-24-2

Troubleshooting Section

Test Step 6. Disconnect the 6V-2197

Idle shutdown

Magnetic Transducer Before Exiting the

"Monitor/Calibrate Timing" Screen on

Operation of the air inlet heater

Cat ET

Secure idle theft deterrent

A. Disconnect the timing probe from the J400

Trip data

engine timing calibration connector.

Maintenance data

B. Install the cover for the J400 connector.

With SEP00 and newer software, there are two

C. Exit the timing calibration screen on Cat ET.

different methods that can be used to obtain the

information for the ECM to use for calculating

Note: Exiting the timing calibration screen on Cat ET

vehicle speed. The ECM can calculate vehicle

will drop the engine rpm to the programmed low idle

speed by either of the following means:

if the cruise control switches were used to maintain

engine rpm during calibration. This is normal.

The ECM monitors the signal from a vehicle

speed sensor in pulses per kilometer (mile). The

Expected Result:

vehicle speed sensor is connected to the ECM

vehicle speed input circuit (terminals 32 and 33).

The magnetic transducer was disconnected before

This is the "Vehicle Speed Calibration" option.

exiting the timing calibration screen on Cat ET.

The ECM receives a J1939 Datalink Broadcast

Results:

Message from the Transmission ECU that

indicates revolutions per kilometer (mile) of the

OK STOP.

transmission output shaft. This option is only

available with SEP00 and newer software. This is

Not OK If the magnetic transducer is still

the "Vehicle Speed Cal (J1939-Trans)" option.

installed after exiting the timing calibration screen

on Cat ET, vehicle speed diagnostic codes may

Each of these methods require a specific calibration

be generated.

number to be programmed into the ECM to calculate

vehicle speed. For the "Vehicle Speed Calibration"

Repair: If vehicle speed diagnostic codes are

option that uses the vehicle speed sensor, the

generated, the vehicle speed diagnostic codes

ECM must know the number of pulses that are

should be cleared.

produced by the vehicle speed sensor during each

kilometer (mile) of travel by the vehicle. In order

STOP.

to find the number of pulses that are produced

by the sensor, multiply the tire size by the axle

i01642395

ratio. Multiply the number that was obtained in the

previous calculation by the number of teeth on the

Vehicle Speed Circuit -

output shaft that is used by the sensor to obtain the

Calibrate

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

SMCS Code: 7493-524

travel by the vehicle. This can be calculated by one

of the following methods:

System Operation Description:

Divide the pulses per kilometer (mile) of the

The ECM uses vehicle speed information for the

sensor on the transmission output shaft by the

following features:

number of teeth on the transmission output shaft.

Cruise control

Multiply the axle ratio by the number of revolutions

per kilometer (mile) of the tire.

Fast idle control

The ECM calculates vehicle speed by converting the

Idle speed control

vehicle speed signal to kilometers per hour (km/h)

or miles per hour (mph). The conversion factor is

PTO operation

customer programmable and the conversion factor

is stored in pulses per km (PPKM) or pulses per

Vehicle speed limiting

mile (PPM).

Speedometer

Progressive shift