Diagnostic Aids

Tech 1(R) scan tool should indicate a vehicle speed whenever the drive wheels are turning at greater than 3 MPH.

A problem in circuit 389 will not affect the VSS input or readings on scan tool. Check circuits 400 and 401 for proper connections. Ensure connections are clean and tight, and harness is routed correctly.

DTC 72 is set when PCM detects a loss of the VSS signal as vehicle is moving at road speeds. This would typically indicate a hardware or circuit failure rather than a software or calibration error.

Fig 1: Code 72 Schematic (3.1L) Vehicle Speed Sensor Circuit

Fig 2: Code 72 Diagnostic Flow Chart (3.1L) Vehicle Speed Sensor Circuit