P0720

Circuit Description
The Output Shaft Speed Sensor provides the Powertrain Control Module (PCM) with an AC voltage input whenever the drive wheels rotate. The frequency of the AC voltage signal increases with wheel speed. The PCM calculates the vehicle speed from the frequency of the AC signal. The PCM uses the above information in order to determine shift points.

Conditions for Setting the DTC
^ When the 4L switch is open, no Output Shaft Speed Sensor signal is received when the VSS (speedometer) signal is received.
^ When the 4L switch is open, no Output Shaft Speed Sensor signal is received when the engine runs at higher than torque converter stall speed in DRIVE range. Torque converter stall speed is 2300-2600 RPM.

Action Taken When the DTC Sets
^ DTC P0720 stores.
^ The PCM enters fail-safe mode.
^ The Malfunction Indicator Lamp (MIL) turns ON. The PCM uses the VSS (speedometer) for shift control during fail-safe mode operation.

Diagnostic Aids
Inspect for the following conditions:
^ A faulty output shaft speed sensor
^ Faulty electrical circuits between the output shaft speed sensor and the PCM
^ A faulty PCM

The following conditions may cause an intermittent:
^ A reduced connection
^ Rubbed through wire insulation
^ A broken wire inside the insulation

Inspect the PCM harness connectors for the following conditions:
^ Backed out terminals
^ Improper mating
^ Broken locks
^ Improperly formed or damaged terminals
^ Reduced terminal-to-wire connections

If DTC P0720 cannot duplicate, the information included in the Freeze Frame data may be useful in determining the vehicle operating conditions when the DTC set.

DTC Confirmation Procedure
1. Turn the ignition switch to the LOCK position.
2. Connect the scan tool to the data link connector (DLC).
3. Turn the ignition switch ON.
4. Use the scan tool in order to clear the following items:
^ DTC P0720
^ Any pending DTCs
5. Start the engine.
6. Shift the transfer case to the 2H position.
7. Drive the vehicle to at least 40 km/h (25 mph) in Drive (D) range for at least 10 seconds.
8. Stop the vehicle.
9. Use the scan tool in order to test for a pending DTC.

Test Description
The numbers below refer to the step numbers on the diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. The scan tool creates an electronic copy of the data taken when the fault occurred. The information then stores in the scan tool for later reference.
2. This step is to verify that the scan tool can read the PCM input information from the output shaft speed sensor.
3. This step tests for a faulty output shaft speed sensor (See the above figure).
4. This step tests for an open in the WHT wire.
5. This step tests for an open in the ORN wire.
6. This step tests for a faulty PCM.
7. This step measures the voltage output of the output shaft speed sensor.