DTC 24

Chart - Code 24 Vehicle Speed Sensor:

Wiring Diagram for Vehicle Speed Sensor:

CODE 24 - VEHICLE SPEED SENSOR (VSS) CIRCUIT


Circuit Description:
The Vehicle Speed Sensor (VSS) consists of a Permanent Magnet (PM) Generator, Buffer, Speedometer, and Electronic Control Module (ECM). The PM Generator is a permenant magnet assembly attached to the transaxle. As the vehicle moves, the generator creatrs a "sine wave" electrical pulse, which is routed to the buffer. In the buffer, the signal is changed from a "sine wave" to a "square wave" and amplified. The square wave is an "ON/OFF" signal. The length of time between pulses determines vehicle speed. The ECM sends out a 12 volt signal out from terminal A 10. The frequency, by which the signal is pulsed low, is used by the ECM to determine vehicle speed.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. Code 24 will set if vehicle speed equals 0 mph when:
Engine speed is between 1500 and 4000 rpm.
TPS reading shows closed throttle.
Low load condition (Low Air Flow).
Not in park or neutral.
All conditions met for 20 seconds.
2. This step checks to see if the fault is in CKT between ECM terminal A10 and VSS buffer terminal F, including the ECM or the VSS/Buffer circuit. The ECM is the source of 12 volts to the buffer in a normal working system.

NOTE: Disregard a Code 24 that sets when the drive wheels are not turning.



Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.
Check for:
Poor connection or damaged harness, inspect ECM harness connector terminal "A1O" for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Intermittent Test If connections and harness check out OK, raise front wheels, block other wheels, idle engine in low gear and "Scan" vehicle speed, while moving related connectors and wiring harness. If the failure is induced, the "Vehicle Speed" display will change. This may help to isolate the location of the malfunction.

A problem with the Park/Neutral switch can result in a Code 24. See Chart C-1A Park/Neutral Switch Diagnosis.