Code 24 - Vehicle Speed Sensor
The ECM applies and monitors 12 volts on circuit No. 437 to Vehicle Speed Sensor (VSS). VSS alternately opens and grounds circuit No. 437 when drive wheels are turning. This pulsing action takes place about 2000 times per mile and ECM calculates vehicle speed based on time between pulses. "Scan" tester reading should closely match speedometer reading.
CAUTION:
To avoid damaging drive axle CV joints, control arms must be supported when wheels are turning off of ground.
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- This test monitors ECM voltage on circuit No. 437. With drive wheels turning, pulsing action varies voltage. This variation is greater at low speeds to an average of 4-6 volts at about 20 mph (32 km/h). Cruise control must be off for accurate test results.
- This test checks for a grounded circuit. A voltage of less than one volt indicates that circuit No. 437 is shorted to ground. Disconnect circuit No. 437 at VSS. The VSS is faulty if voltage now reads more than 10 volts. If voltage remains less than one volt, circuit No. 437 is grounded. If circuit is not grounded, check for a faulty ECM connector or ECM.
- A steady 8-12 volts at ECM connector indicates circuit No. 437 is open, or a faulty VSS.
- This is a normal voltage condition and indicates a possible intermittent condition.
- This step will isolate whether problem is in circuit No. 437 or ECM.
NOTE:
To prevent misdiagnosis, the technician should review electrical section or electrical troubleshooting manual and identify the type of vehicle speed sensor used prior to using this chart. Disregard Code 24, if set when drive wheels are turning.
- No fault found. See INTERMITTENTS in TROUBLE SHOOTING section.