8206noco.fm Page 179 Thursday, July 2, 1998 1:19 PM
SYMPTOM RELATED DIAGNOSTICS BUFFERED MPH (continued) Test 32
Test 64
Checking for proper voltage to the speedometer when the truck is moving
Checking for a loose connection 1. Reconnect the speedometer. 2. Test drive the vehicle.
If the speedometer is now working, testing has apparently corrected a loose connection. Recheck all connectors to ensure proper connections. If the speedometer is still not working, proceed to Test 128.
Test 128 Checking for a defective speedometer or V-MAC II module 1. Install a speedometer that is known to be good. Make sure the dip switches on the back of the speedometer are set properly. 2. Test drive the vehicle.
If the speedometer is now working, replacing the speedometer has corrected the problem. If the speedometer is not working, reinstall the original speedometer and replace the V-MAC II module. Retest to be sure the problem has been corrected.
Figure 297 — Speedometer Connector
1. Remove the jumper between J1B connector pins P1 and W2. 2. Reconnect the J1B connector. 3. Turn the ignition key to the ON position. 4. Measure the voltage on the buffered MPH line on the speedometer connector while the vehicle is being driven at more than 10 mph.
If the voltage is between 1.75 and 3.25 volts, proceed to Test 64. If the voltage is not within this range, replace the V-MAC II module. Retest to be sure the problem has been corrected. Page 179
