DTC 24

Code 24 Diagnostic Chart:

Vehicle Speed Sensor (VSS) And Park/Neutral Switch Circuit Diagram:

CIRCUIT DESCRIPTION
Vehicle speed information is provided to the ECM by the vehicle speed sensor which uses a Permanent Magnet (PM) generator and is mounted in the transaxle. The PM generator produces a pulsing voltage whenever vehicle speed is over about 3 mph. The AC voltage level and the number of pulses increases with vehicle speed. The ECM then converts the pulsing voltage to mph which is used for calculations and the mph can be displayed with a scan tool. Output of the generator can also be seen by using a digital voltmeter on the AC scale while rotating the generator.

The function of VSS buffer used in past model years has been incorporated into the ECM. The ECM then supplies the necessary signal to the instrument panel (4000 pulses per mile) for operating the speedometer and the odometer. If the vehicle is equipped with cruise control, the ECM also provides a signal (2000 pulses per mile) to the cruise control module.


NOTE: To prevent misdiagnosis, Disregard a DTC 24 set when drive wheels are not turning.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. DTC 24 will set if vehicle speed equals 0 mph when:
^ VSS indicates less than 3 mph.
^ MAP is less than 30 kPa.
^ Engine speed is between 2200 and 4400 RPM.
^ TP sensor is less than 2%.
^ Not in park or neutral.
^ No DTC 21, 22, 33 or 34.
^ All conditions met for 3 seconds.

NOTE: These conditions are met during a road load deceleration. Disregard DTC 24 that sets when drive wheels are not turning. The PM generator only produces a signal if drive wheels are turning greater than 3 mph.

2. If CKTs 400, 401 and 389 are OK, and if the speedometer works properly, DTC 24 is being caused by a faulty ECM, faulty PROM or an incorrect PROM.

DIAGNOSTIC AIDS:

^ Tech 1 scan tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph.

^ A problem in CKT 389 will not affect the VSS input or the readings on a Tech 1 (or equivalent) scan tool.

^ Check CKT 400 and CKT 401 for proper connections to be sure there clean and tight and the harness is routed correctly. Refer to "Intermittents" in "Symptoms".

^ (A/T) A faulty or misadjusted Park/Neutral Position (PNP) switch can result in a false DTC 24. Use a Tech 1 (or equivalent) scan tool and check for proper signal while in overdrive (4T60E-T4). Refer to CHART C-1A for PNP switch diagnosis check. Chart C-1A Park/Neutral Switch Diagnosis