Intermittent Failure

Fig. 19 Speed sensor wiring circuit. Models with mechanical speedometer:

Fig. 20 Speed sensor wiring circuit. Models with digital speedometer:

If this code is not displayed during the third pass of diagnostic codes, the problem is an intermittent failure. To help isolate the problem, lift drive wheels and allow vehicle to idle in low gear. Manipulate related wiring while observing parameter .1.2. If the failure is induced, the vehicle speed reading will drop from its normal value to a reading of 0 mph.
The speed sensor generates an electrical signal representative of vehicle speed and the buffer amplifier amplifies and inverts this signal for use by the ECM. Code 24 indicates that the speed signal is not being received by the ECM when the vehicle is in fourth gear. Possible causes of this condition are:
a. Defective speed sensor.
b. Defective buffer amplifier.
c. Defective wiring, or electrical connectors.
d. ECM unable to process the speed signal.
e. Inoperative speedometer.