Transmission / OSS

TRANSMISSION OUTPUT SPEED SENSOR

Measures output-shaft speed for ratio, shift and vehicle-speed calculations.

SENSOR GUIDE22/86

Identify the circuit first

ONE NAME.
DIFFERENT SIGNALS.

Pin count is a clue, not proof. Confirm the exact architecture before resistance testing, applying voltage or judging the waveform.

TYPE 01CONSTRUCTION VARIANT

Two-wire inductive / passive

Confirm wiring, pin count and service information before testing.

The coil generates an AC voltage; it has no external power supply.

Reading the signal

Good waveform

Compare the measured signal with the specified input or command under the same operating conditions. Levels, timing and repeatability should match the installed design and a suitable verified reference. There is no universal waveform or scale for every version of this component.

Faulty waveform

An unexplained dropout, missing response, excessive noise or mismatch between command and feedback warrants further testing. First rule out a changed physical condition, incorrect probe reference, supply loss and an unsuitable scope setting; an unusual trace alone does not identify a failed component.

TYPE-SPECIFIC TESTS

+ Measure resistance only when permitted, then scope both wires while rotating. Amplitude must rise with speed and the air gap matters.

+ Verify the specified supply, ground, bias or termination before judging the signal.

+ Repeat the test through the complete operating range.

EXPECTED

✓ Output matches this construction type

✓ Stable levels and repeatable response

✓ Agreement with related scan data

COMMON FAULTS

— Incorrect test method for the sensor type

— Supply, ground or signal-circuit fault

— Installation, target or calibration concern

TYPE 02CONSTRUCTION VARIANT

Three-wire Hall / active

Confirm wiring, pin count and service information before testing.

A supply and ground power a digital output that switches high and low.

Reading the signal

Good waveform

Logic levels and edge transitions are consistent with the installed circuit. Pulse timing changes in the specified way as the input changes; intended index gaps or encoded features repeat correctly.

Faulty waveform

Missing or extra edges, weak switching levels, intermittent pulse loss or a stuck level can indicate supply, ground, wiring, target or sensor problems. A steady level can be normal when the target is stationary. Decode encoded signals using the correct protocol.

TYPE-SPECIFIC TESTS

+ Verify loaded supply and ground, then scope the signal at the sensor and controller.

+ Verify the specified supply, ground, bias or termination before judging the signal.

+ Repeat the test through the complete operating range.

EXPECTED

✓ Output matches this construction type

✓ Stable levels and repeatable response

✓ Agreement with related scan data

COMMON FAULTS

— Incorrect test method for the sensor type

— Supply, ground or signal-circuit fault

— Installation, target or calibration concern

TYPE 03CONSTRUCTION VARIANT

Two-wire magnetoresistive / active

Confirm wiring, pin count and service information before testing.

The module reads a current-modulated signal from a powered two-wire element.

Reading the signal

Good waveform

The measured signal changes consistently with the physical input and stays within the application-specific operating range. Under a steady input, it should remain stable apart from normal noise or control activity.

Faulty waveform

Dropouts, unexpected spikes, a signal pinned near a supply rail, or a biased reading can indicate a problem. Verify the real input, reference and loaded ground before blaming the sensor; a smooth signal can still be inaccurate.

TYPE-SPECIFIC TESTS

+ Use the specified current or voltage conversion method. Do not judge it as an inductive sensor.

+ Verify the specified supply, ground, bias or termination before judging the signal.

+ Repeat the test through the complete operating range.

EXPECTED

✓ Output matches this construction type

✓ Stable levels and repeatable response

✓ Agreement with related scan data

COMMON FAULTS

— Incorrect test method for the sensor type

— Supply, ground or signal-circuit fault

— Installation, target or calibration concern

Correct theory and operation

HOW IT
WORKS.

Understand the sensing method, circuit and controller strategy before interpreting data or replacing the component.

01

Measured condition

Measures output-shaft speed for ratio, shift and vehicle-speed calculations.

02

Signal type

Digital or AC speed signal. A Hall, magnetoresistive or inductive element produces pulses whose frequency follows rotational speed.

03

Controller use

The receiving controller checks range, rationality and rate of change against related inputs before setting a fault or substituting a value.

04

Installation matters

Mounting, target condition, air gap, contamination, temperature, shielding or calibration may affect the result even when the circuit is intact.

Common mistakes

AVOID THE
FALSE CLUE.

COMPLETE TEST SEQUENCE

  1. Identify Hall, magnetoresistive or inductive construction.
  2. Verify supply and ground when required.
  3. Scope the signal while rotating the component.
  4. Compare frequency, amplitude and dropout behavior with related speed inputs.
  5. Repeat the original operating condition and confirm the repair.
DO NOT CONDEMN THE SENSOR

Prove its supply, ground, signal path, physical input and calibration before replacement. Vehicle-specific specifications always win.

SENSOR LIBRARYReturn to all sensors→

Diagnostic details

Purpose

Output shaft speed is used for shift scheduling, gear-ratio calculations and vehicle-speed information on many systems.

Scan tool data

  • Output shaft speed
  • Vehicle speed
  • Input shaft speed
  • Commanded gear
  • Actual gear ratio

Failure symptoms

  • Erratic shifting
  • Incorrect speed information
  • Failsafe operation
  • Gear-ratio faults

Related DTCs

  • P0720 – Output Speed Sensor Circuit
  • P0721 – Output Speed Sensor Range/Performance
  • P0722 – Output Speed Sensor No Signal
  • P0723 – Output Speed Sensor Intermittent

Diagnostic tips

  • Compare OSS with vehicle speed and ISS.
  • Check the tone wheel or magnetic target when accessible.

Construction & type-specific testing

Identify the installed design before testing. Construction, signal format and redundant channels are separate attributes; use only the procedure for the actual component.

Hall Effect

Powered digital output-speed sensor.

Operating principle

  • The rotating target changes the magnetic field.
  • The sensor produces a digital pulse train.
  • Frequency represents output shaft speed.

Circuit identification

Typically 3 wires

Wiring

  • Power/reference

Expected readings

  • Pulse frequency increases with output shaft speed.
  • Signal should contain clean high and low states.

Multimeter testing

  • Verify power.
  • Verify ground.
  • Check frequency where appropriate.

Oscilloscope setup

  • DC coupling
  • Edge trigger
  • Adjust time base for vehicle speed

Oscilloscope testing

  • Look for consistent pulses.
  • Watch for dropout as vehicle speed changes.

Waveform interpretation

Typical Hall-effect transmission output-speed waveform.

Common failures

  • Power or ground fault
  • Signal circuit fault
  • Internal sensor failure
  • Target damage

Diagnostic tips

  • An intermittent OSS may be easier to identify by graphing scan data during a road test.
Variable Reluctance

Passive magnetic output-speed sensor.

Operating principle

  • A rotating target induces AC voltage in the sensor.
  • Frequency represents shaft speed.

Circuit identification

Typically 2 wires

Wiring

  • Signal positive
  • Signal negative

Expected readings

  • AC frequency increases with shaft speed.
  • Amplitude generally increases with speed.

Multimeter testing

  • Check resistance only when specifications are available.
  • Check AC output when appropriate.

Oscilloscope setup

  • AC coupling can be useful
  • Connect across both signal circuits
  • Adjust time base with speed

Oscilloscope testing

  • Look for consistent AC pulses.
  • Check for missing pulses.
  • Check signal amplitude.

Waveform interpretation

Typical variable-reluctance output-speed sensor waveform.

Common failures

  • Open winding
  • Excessive air gap
  • Target damage
  • Metal contamination

Diagnostic tips

  • Compare the signal against vehicle speed and other wheel/speed data.