Code 72, Vehicle Speed Sensor Loss - 3.4L "F" Body, 4.3L & 5.7L "B", "D" & "F" Bodies

Fig 1: Code 72, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp.

Fig 2: Code 72, Circuit Diagram (4.3L & 5.7L B Body) Courtesy of General Motors Corp.

Fig 3: Code 72, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp.

Fig 4: Code 72, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp.

Fig 5: Code 72, Flow Chart (B, F & D Bodies) Courtesy of General Motors Corp.

Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than about 2 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

1. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals.
2. Ensure harness is routed away from hot exhaust components.
3. If software/calibration is incorrect, code will set. Ensure calibration is correct before replacing PCM.