Transmission / ISS

TRANSMISSION INPUT SPEED SENSOR

Measures turbine or input-shaft speed for slip, ratio and shift control.

SENSOR GUIDE21/86

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 turbine or input-shaft speed for slip, ratio and shift control.

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

Input speed allows the transmission controller to calculate gear ratio, monitor torque-converter operation and determine whether the transmission is responding correctly to shift commands.

Scan tool data

  • Input or turbine speed
  • Engine RPM
  • Output shaft speed
  • Commanded gear
  • Actual gear ratio
  • Torque converter slip when available

Failure symptoms

  • Harsh shifting
  • Incorrect shift timing
  • Failsafe operation
  • Gear-ratio faults
  • Speed-sensor DTCs

Related DTCs

  • P0715 – Input/Turbine Speed Sensor Circuit
  • P0716 – Input/Turbine Speed Sensor Range/Performance
  • P0717 – Input/Turbine Speed Sensor No Signal
  • P0718 – Input/Turbine Speed Sensor Intermittent

Diagnostic tips

  • Compare input speed with engine RPM and output speed.
  • Internal transmission problems can create incorrect gear ratios even when both speed sensors are operating correctly.
  • Identify sensor technology before electrical testing.

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 transmission speed sensor.

Operating principle

  • A rotating target changes the magnetic field at the Hall element.
  • Sensor electronics generate a digital pulse train.
  • Pulse frequency increases as shaft speed increases.

Circuit identification

Typically 3 wires

Wiring

  • Power/reference
  • Digital signal

Expected readings

  • Signal frequency should increase with shaft speed.
  • The digital signal should have distinct high and low states.

Multimeter testing

  • Verify power.
  • Verify ground.
  • A frequency-capable meter may be useful.
  • A meter may miss short-duration signal dropouts.

Oscilloscope setup

  • DC coupling
  • Edge trigger
  • Voltage scale appropriate to signal level
  • Adjust time base according to shaft speed

Oscilloscope testing

  • Look for clean digital transitions.
  • Verify increasing frequency as speed rises.
  • Look for missing pulses or intermittent dropout.

Waveform interpretation

Typical Hall-effect transmission input-speed digital waveform.

Common failures

  • Sensor power loss
  • Ground fault
  • Signal circuit fault
  • Internal sensor failure
  • Damaged target

Diagnostic tips

  • Graph input and output speed together when diagnosing gear-ratio problems.
Variable Reluctance

Passive magnetic speed sensor producing an AC waveform.

Operating principle

  • A rotating toothed target changes magnetic flux through the sensor.
  • The sensor generates AC voltage.
  • Signal frequency and generally amplitude increase with shaft speed.

Circuit identification

Typically 2 wires

Wiring

  • Signal positive
  • Signal negative

Expected readings

  • An AC waveform should be produced while the shaft rotates.
  • Signal amplitude generally increases with speed.

Multimeter testing

  • Resistance testing may be used when the manufacturer provides specifications.
  • AC voltage can be checked while rotating when appropriate.

Oscilloscope setup

  • AC coupling can be useful
  • Connect across the signal circuits
  • Adjust voltage scale for signal amplitude
  • Adjust time base for shaft speed

Oscilloscope testing

  • Look for a consistent AC waveform.
  • Check for missing or distorted pulses.
  • Watch for low amplitude.

Waveform interpretation

Typical variable-reluctance input-speed sensor AC waveform.

Common failures

  • Open winding
  • Excessive air gap
  • Metal debris
  • Damaged target

Diagnostic tips

  • Low shaft speed can result in relatively low signal amplitude.