DTC 24

Code 24 Chart:

Wiring Diagram For VSS:

CIRCUIT DESCRIPTION:

The ECM applies and monitors 12.0 volts on circuit 437. Circuit 437 connects to the Vehicle Speed Sensor (VSS), which alternately grounds circuit 437 when the drive wheels are turning. This pulsing action takes place about 3683 times per mile, and the ECM will calculate vehicle speed based on the time between pulses.

1. Code 24 will set if:
a. No malfunction Codes 21, 22, 33, or 34.
b. Speed sensor indicates less than 5 mph.
c. Engine speed is between 1500 and 4400 rpm on a 1.6L engine, or between 2000 and 4400 rpm on a 2.0L engine.
d. Park/Neutral indicates not in park or neutral.
e. Coolant temperature is greater than 85°C (185°F).
f. MAP sensor has less than 49 kPa (7.0 psi) on a 1.6L engine, or less than 23 kPa (3.0 psi) on a 2.0L engine.
g. All conditions must be met for 3 seconds.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This test uses the "Scan" tool to verify the VSS sensor operation.
2. The ECM supplies 12.0 volts to circuit 437, but this signal should not illuminate the test light. This step verifies that circuit 437 is not shorted to a voltage source.
3. By probing circuit 437 with a test light several times a second, a vehicle speed signal should be generated and displayed on the "Scan" tool.
4. This test must be done using a voltmeter. This will check for 12.0 volts being supplied to circuit 437 by the ECM.
5. Circuit 439 is the ignition feed that supplies operating power to the VSS.
6. Circuit 450 supplies the ground path for VSS operation. If circuit 450 is open, VSS cannot pulse circuit 437 to ground.


DIAGNOSTIC AIDS:

1. A faulty or misadjusted park/neutral switch can result in a false Code 24. Use a "Scan" tool and check for a proper signal while in drive or overdrive. See CHART C-1A for P/N switch diagnosis.
2. The "Scan" tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 mph.
3. If a Code 24 is intermittent, see DIAGNOSIS BY SYMPTOM.