DTC 72

DTC 72 Chart:

Vehicle Speed Sensor Circuit:

Circuit Description:
Vehicle speed information is provided to the Powertrain Control Module (PCM) by the Vehicle Speed Sensor (VSS), which is a Permanent Magnet (PM) generator mounted in the transmission. The PM generator produces a pulsing voltage whenever vehicle speed is over about 3 mph. The AC voltage level and the number of pulses increases with vehicle speed. The PCM then converts the pulsing voltage to mph, which is used for calculations. The vehicle speed can be displayed with a Tech 1 scan tool.

The PCM supplies a signal, on CKT 817, to operate the speedometer and the odometer. The VSS signal is also sent to the cruise control module.

DTC 72 Will Set When:
Not in P/N, transmission output speed changes greater than 1000 RPM, or in P/N, transmission output speed change greater than 2048 RPM. No DTC 28, and engine speed greater than 200 RPM. All conditions met for 2 seconds.

Action Taken (PCM will default to):
A delayed (soft) landing to third gear and maximum line pressure. DTC 72 will be stored in the PCM memory but will not turn "ON" the Malfunction Indicator Lamp (MIL).

DTC 72 Will Clear When:
The fault condition(s) no longer exist, and the ignition switch is cycled "OFF" then "ON."

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. This test checks the function of the VSS circuit.

2. An intermittent connection at the VSS or PCM may cause a DTC 72 to set. Inspect the harness and all related connections. Check for damaged or pushed out terminals.

3. This test checks to make sure the wire harness is routed away from the exhaust manifold.

4. This test checks for an incorrect PROM or a poor connection.

Diagnostic Aids:
- DTC 24 will set when no vehicle speed is detected at start off.
- DTC 72 will set when vehicle speed has been detected and is lost.