DTC 24

Chart - Code 24 Vehicle Speed Sensor:

Wiring Diagram for Vehicle Speed Sensor Circuit.:

CODE 24 - VEHICLE SPEED SENSOR (VSS) CIRCUIT


Circuit Description:
The Electronic Control Module (ECM) applies and monitors 12 volts on CKT 437. CKT 437 connects to the Instrument Panel (IP) Vehicle Speed Sensor (VSS), which alternately grounds CKT 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between "Pulses". The IP cluster receives the vehicle speed signal from a Permanent Magnet (PM) generator mounted in the transmission. A "Scan" tool reading should closely match with speedometer reading with drive wheels turning.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.
1. Code 24 will set if:
CKT 437 voltage is constant
Engine speed between 900 and 4400 rpm
Closed throttle Low load condition (low air flow)
Not in park or neutral
All conditions must be met for 2 seconds
These conditions are met during a road load deceleration.

2. A voltage of less than 1 volt at the 6-way connector indicates that the CKT 437 wire may be shorted to ground. Disconnect CKT 437 at the IP cluster. If voltage now reads above 10 volts, the IP cluster is faulty. If voltage remains less than 10 volts, then CKT 437 wire is grounded or open. If 437 is not grounded or open, check for a faulty ECM connector or ECM.


Diagnostic Aids:

If "Scan" displays vehicle speed, check park/neutral switch CHART C-lA on vehicle with auto transmisssion. If switch is OK, check for intermittent connections. An open or short to ground in CKT 437 will result in a Code 24. If the customer also complained about a loss of mph on the IP, check the PM generator circuit. See WIRING DIAGRAMS. Also refer to "Intermittents" in DIAGNOSIS BY SYMPTOMS - NO TROUBLE CODE STORED.