GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Optra 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0720

Circuit Description

The vehicle automatic transmission (A/T) output speed sensor (OSS) is a magnetic inductive pickup that relays information relative to vehicle speed to the transmission control module (TCM).

Vehicle speed information is used by the TCM to control shift timing, line pressure, and torque converter clutch (TCC) apply and release.

The output speed sensor mounts in the case at the speed sensor rotor, which is pressed onto the spur gear. An air gap of 0.1 mm-1.3 mm (0.004-0.05 in) is maintained between the sensor and the teeth on the spur gear teeth. The sensor consists of a permanent magnet surrounded by a coil of wire. As the differential rotates, an AC signal induces a higher frequency and voltage measurement at the sensor. Sensor resistance should measure R at 20°C (68°F). Sensor can measure from 20-8,000 Hz.

Conditions for Setting the DTC
    • Output speed is greater than 9,762 RPM.
    • System voltage is too high or too low.
    • CAN transmitting wiring harness shortage or open
    • The TCM or engine control module (ECM) is defective.
    • Immediately after the above condition occurs

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate
    • The TCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Failure Records buffer.
    • Adopt Emergency/Substitute mode and constant 4th gear by hydraulic control.
    • Open lock up clutch

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF when the malfunction has not occurred after 3 ignition cycles.
    • A history DTC will clear after 40 consecutive warm-up cycles without a fault.
    • Using a scan tool can clear history DTCs.

Diagnostic Aids

When DTC P0720 sets, the possible cause of fault could be the output speed sensor (OSS).

P0720

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

--

Go to Step 2

Go to Diagnostic System Check - Vehicle

2
  1. Install the scan tool.
  2. Turn the ignition ON, with the engine OFF.
  3. Record then clear the DTCs.
  4. Turn the ignition OFF.
  5. Raise and support the drive wheels.
  6. Start the engine.
  7. Shift into gear position D. Observe the output speed on the scan tool.

Is the speed within the specified value?

190-9,762 RPM

Go to Diagnostic Aids

Go to Step 3

3
  1. Turn the ignition OFF.
  2. Disconnect the transaxle wiring connector.
  3. Measure the resistance between terminals 1 and 2 of the transaxle wiring connector.

Is the resistance within the specified value?

825-835 ohms

Go to Step 9

Go to Step 4

4
  1. Remove the oil pan.
  2. Disconnect the output speed sensor wiring connector.
  3. Measure the resistance between terminal 1 of the output speed sensor wiring connector and terminal 1 of the transaxle wiring connector.
  4. Measure the resistance between terminal 2 of the output speed sensor wiring connector and terminal 2 of the transaxle wiring connector.

Is the resistance approximately equal to the specified value?

0 ohms

Go to Step 6

Go to Step 5

5

Repair the malfunctioning terminals, as necessary.

Is the action complete?

--

System OK

--

6
  1. Turn the ignition ON, with the engine OFF.
  2. Measure the voltage of terminal 1.
  3. Measure the voltage of terminal 2.

Is the voltage within the specified value?

11-14 V

Go to Step 7

Go to Step 8

7

Repair the malfunctioning terminals, as necessary.

Is the action complete?

--

System OK

--

8

Replace the output speed sensor.

Is the action complete?

--

System OK

--

9
  1. Disconnect the transaxle wiring connector and transmission control module (TCM) connector.
  2. Measure the resistance between terminal 1 of the transaxle wiring connector and terminal B10 of the TCM wiring connector.
  3. Measure the resistance between terminal 2 of the transaxle wiring connector and terminal B5 of the TCM wiring connector.

Is the resistance approximately equal to the specified value?

0 ohms

Go to Step 11

Go to Step 10

10

Repair the malfunctioning terminals, as necessary.

Is the action complete?

--

System OK

--

11
  1. Turn the ignition ON, with the engine OFF.
  2. Measure the voltage of terminal 1.
  3. Measure the voltage of terminal 2.

Is the voltage within the specified value?

11-14 V

Go to Step 12

Go to Step 13

12

Repair the malfunctioning terminals, as necessary.

Is the action complete?

--

System OK

--

13

Replace the TCM. Refer to Transmission Control Module Replacement .

Is the action complete?

--

Go to Step 14

--

14
  1. After the repair, use a scan tool "clear info" function.
  2. Road test the vehicle.
  3. Review the DTC info.

Has the last test failed or is the current DTC displayed?

--

Go to Step 2

System OK