Illustration 181 Schematic for a single coil speed sensor and an ECM driven speedometer

410

TM 9-2320-312-24-2

Troubleshooting Section

With SEP00 and newer software, the ECM can be

configured to receive vehicle speed information

from an Electronic Transmission Control Unit via the

J1939 data link. The transmission must be capable

of supporting the "J1939 ETC1 Broadcast Message

(PGN 61,442 Bytes 2 & 3)". This message provides

the speed of the transmission output shaft. This

feature requires the hardware for the J1939 data

link to be installed in the chassis of the vehicle. This

also requires a transmission that is electronically

controlled and capable of supporting the necessary

J1939 protocol.

When the engine is configured for the J1939

option, the circuit for the ECM vehicle speed input

(terminals 32 and 33) will be ignored. The ECM uses

the "Vehicle Speed Cal (J1939-Trans)" parameter

value in order to calculate vehicle speed. The ECM

uses the parameter value and the speed of the

output shaft that is received over the J1939 data

link to calculate the vehicle speed. The "Vehicle

Speed Cal (J1939-Trans)" parameter is based on

the revolutions per mile of the output shaft. There

are several methods that can be used to arrive

at this calibration value. Refer to Troubleshooting,

"Vehicle Speed Circuit - Calibrate" for details.

Regardless of the source that is used to determine

vehicle speed, the ECM uses the calculated value

for the vehicle speed in the same manner to control

several features and functions. The diagnostics for

vehicle speed function very similarly when either a

hard-wired signal is provided to the ECM from a

speed sensor, or a message is sent to the ECM via

the J1939 data link. If the ECM detects a loss of

vehicle speed or a value that is invalid, a fault code

will be logged in order to alert the operator or the

technician of the presence of a problem.

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Illustration 181

Schematic for a single coil speed sensor and an ECM driven speedometer