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Probable Cause - No speed messages from the Engine ECU.
Procedure:
1. Switch the ignition on and wait for the initialization to end.
2. When the SMC pointer begins to sweep, wait for 3 minutes to see if a NO DATA
message appears. Do not press the Select or Reset buttons during this time.
3. If a NO DATA message appears, then go to Section 5.5.8.
4. If a NO DATA message does not appear, connect the HDT to the diagnostic
connector and see if the Engine ECU is placing road speed data on the J1708 data
bus.
a. If road speed data is present, replace the SMC.
b. If road speed data is not present, check the Engine ECU by following the
engine manufacturer's diagnostic procedures.
Probable Cause - J1708 data bus open between the Engine ECU and the SMC.
Procedure:
1. Switch the ignition on and wait for the initialization to end.
2. When the SMC pointer begins to sweep, wait for 3 minutes to see if a NO DATA
message appears. Do not press the Select or Reset buttons during this time.
3. If a NO DATA message does not appear, then go to Section 5.5.7.
4. If a NO DATA message does appear, switch the ignition off.
5. Open the dash panel and unplug the 6-pin connector from the rear of the SMC.
6. Place a jumper from the 6-pin harness connector pin 3 (J1708 Bus +) to pin 5
(J1708 Bus –).
7. Unplug the Engine ECU and locate J1708 data bus circuit wires 417 and 418.
8. Use an ohmmeter to measure the resistance between circuit wires 417 and 418.
a. If more that about 10 ohms are measured, the wiring is probably open.
Inspect the wiring harness for open or damaged wires and connector pins.
b. If less than 10 ohms are measured, replace the SMC.
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