Vehicle Speed and Speedometer Circuit

408

TM 9-2320-312-24-2

Troubleshooting Section

4. Repeat the test step.

E. Turn the ignition key switch to the ON position.

5. If the problem is resolved with the test ECM,

F. Access the "AT/MT/HT XMission Interface Test"

reconnect the suspect ECM.

through the following menus:

"Diagnostics"

6. If the problem returns with the suspect ECM,

replace the ECM.

"Diagnostic Tests"

7. Verify that the repair eliminates the problem.

"Special Tests"

STOP.

Note: The "Transmission Style" must be programmed

to "AT/MT/HT Option 1", "AT/MT/HT Option 2",

i01632415

"AT/MT/HT Option 3", or "AT/MT/HT Option 4" for the

Vehicle Speed and

"AT/MT/HT XMission Interface Test" to be available.

This will allow output 7 to control the AT/MT/HT

Speedometer Circuit - Test

transmission relay.

SMCS Code: 7463-081; 7493-081

G. While the voltage test lamp is being observed,

cycle the special test on and off.

System Operation Description:

H. Stop the special test.

Use this procedure under the following situation:

Expected Result:

Use this procedure to troubleshoot the system only

under the following conditions:

The voltage test lamp behaves in the following

manner:

There is an active diagnostic code.

The voltage test lamp turns on when the test is

There is an easily repeated diagnostic code that

active.

is associated with the vehicle speed circuit.

The voltage test lamp turns off when the test is

Refer to Troubleshooting, "Vehicle Speed Circuit -

not active.

Calibrate" if the vehicle speed is being calibrated

in ppm (pulses per mile) or PPKM (pulses per

Results:

kilometer).

Yes The ECM is OK. There is a problem in the

The following background information is related

harness.

to this procedure:

Repair: Perform the following repair:

The vehicle speed circuit consists of the vehicle

speed source and associated wiring. The

Repair the engine harness or replace the engine

vehicle speed source is installed by the vehicle

harness. Verify that the repair eliminates the

OEM. Usually, a sensor reads movement of the

problem.

transmission output shaft from the teeth on a

chopper wheel. The ECM converts the signal from

STOP.

the vehicle speed source into vehicle speed for the

following functions:

No Temporarily connect a test ECM. Repeat this

test step. If the problem is resolved with the test

Cruise control

ECM, reconnect the suspect ECM. If the problem

returns with the suspect ECM, replace the ECM.

Fast idle

Repair: Perform the following repair:

Idle speed control

1. Temporarily connect a test ECM.

Progressive shift

2. Remove all jumpers and replace all connectors.

Speedometer

3. Recheck the system for active diagnostic

PTO operation

codes.