Models With Digital Cluster

1. If digital speedometer is not operating properly, proceed to step 2. If speedometer is operating properly, proceed as follows:
a. Raise one drive wheel of vehicle, then connect voltmeter between pin 2 of red ECM connector and ground.
b. Manually rotate drive wheel with ignition on and gearshift selector in Neutral. Note voltage reading.
c. If voltage does not vary as wheel is rotated, proceed to step 1d. If voltage reading varies between .6 and 11 volts, road test vehicle in 4th gear at 55 mph and enter diagnostics. If Code 24 is still stored hard, replace ECM. If Code 24 is no longer stored hard, there is an intermittent failure in the system.
d. Disconnect buffer amplifier electrical connector and connect voltmeter between pin C of harness connector and ground. If voltages measure 10 to 12 volts, replace buffer amplifier. If no voltage is recorded, check circuit 961 for an open or short to ground. If circuit is satisfactory, check for a faulty ECM or ECM connector and repair or replace as necessary.
2. If speedometer does not operate properly, proceed as follows:
a. Ensure speedometer cable is properly installed.
b. Disconnect buffer amplifier electrical connector, then connect voltmeter between pin D of harness connector and ground. If voltmeter reads 12 volts with ignition on, proceed to step 2c. If no voltage is recorded, check condition of 20 amp GA-TRANS fuse. If fuse is blown, repair short in circuits fed by fuse. If fuse is not blown, repair open in circuit 39.
c. Connect voltmeter between harness connector pins D and E. If voltmeter still reads 12 volts, proceed to step 2d. If no voltage is measured, repair open in circuit 151.
d. Reconnect buffer amplifier and measure voltage at pin G while manually turning speedometer. If voltage does not vary, proceed to step 2e. If voltage varies between 0 and 5 volts, replace buffer amplifier.
e. Measure voltage at connector pin F. If voltmeter reads between 4 and 6 volts, proceed to step 2f. If no voltage is measured, replace buffer amplifier.
f. Measure voltage at connector pin E. If voltage is within 1 volt of pin F, replace buffer amplifier. If voltage at pin E is more than 1 volt less than pin F, check for a faulty speed sensor. If speed sensor is satisfactory, repair or replace speedometer.