Powertrain Controls - ECM/PCM

Trouble Code 24 Chart:

Diagnostic Trouble Code (DTC) 24:

CIRCUIT DESCRIPTION
A vehicle speed signal is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor (VSS). This sensor produces a pulsing waveform voltage whenever vehicle speed is greater than 2 MPH. The voltage level or amplitude and the frequency of pulses increases with vehicle speed. The PCM conditions this signal and calculates the vehicle speed. The PCM will then supply the signal to the instrument panel (4000 pulses per mile).

DIAGNOSTIC TROUBLE CODE (DTC) 24 WILL SET WHEN
DTC 28 is not present, brake is released, engine RPM is greater than 3000, vehicle speed is less than 5 mph with all conditions met for 4 seconds.

ACTION TAKEN (PCM) WILL DEFAULT TO
The vehicle will default to 3rd gear and the Malfunction Indicator Lamp (MIL) will become illuminated.

DTC 24 WILL CLEAR WHEN
A current DTC 24 will clear after each ignition key cycle. A History DTC 24 will clear after 50 consecutive ignition key cycles without a current DTC 24 being stored.

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

1. Disregard DTC 24 that sets when drive wheels are not turning. The sensor only produces a signal if drive wheels are turning faster than 3 MPH.
2. If circuits 400, 401 and 817 are OK, and if the speedometer works properly, DTC 24 is being caused by a faulty PCM, or an incorrect program.

DIAGNOSTIC AIDS
Tech 1 scan tool should indicate a vehicle speed whenever the drive wheels are turning greater than 3 MPH.
A problem in circuit 817 will not affect the VSS input or the readings on a Tech 1 scan tool.
Check circuit 400 and circuit 401 for proper connections to be sure they are clean and tight, and that the harness is routed correctly.
Refer to Computers and Controls / System Diagnosis / Procedures / Diagnosis by Symptom / Intermittents. - Intermittent Malfunctions