Driver demand / APP

ACCELERATOR PEDAL POSITION SENSOR

Multiple redundant position tracks report driver demand to the powertrain controller for electronic throttle control.

FIELD GUIDE06/13

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 01ACTIVE / REDUNDANT ANALOG

Dual Analog APP

Shared or separate references with two/three outputs

Multiple voltages rise together or maintain a specified inverse/ratio relationship.

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

+ Graph every APP track.

+ Sweep slowly and pause at several positions.

+ Verify the specified ratio and shared grounds.

EXPECTED

✓ Correlated smooth tracks

✓ Repeatable endpoints

✓ Stable ratio

COMMON FAULTS

— One-track dropout

— Reference fault

— Connector fretting

TYPE 02ACTIVE / DIGITAL DATA

Digital / SENT APP

Power, ground and one or more digital data circuits

Pedal position is carried in timed data frames rather than a variable DC voltage.

Reading the signal

Good waveform

Check the correct physical interface and decode the transmitted data. Valid frames, expected update timing and measurements that agree with the real input support normal operation. Pulse shape alone does not establish measurement accuracy.

Faulty waveform

Corrupted or missing frames, unexpected pauses, invalid status bits or implausible decoded values can indicate a fault. Verify supply, ground and the applicable bus before replacing the sensor; do not apply CAN waveform expectations to LIN, SENT or another interface.

TYPE-SPECIFIC TESTS

+ Verify powers and grounds.

+ Decode the signal with compatible equipment.

+ Compare decoded position with scan data and pedal travel.

EXPECTED

✓ Valid repeating frames

✓ Position count follows travel

✓ No status or CRC errors

COMMON FAULTS

— Corrupt frames

— Line stuck high/low

— Supply noise

Correct theory and operation

HOW IT
WORKS.

Understand the component, its circuit and the controller's strategy before interpreting the waveform or beginning disassembly.

01

Sensing principle

Multiple redundant position tracks report driver demand to the powertrain controller for electronic throttle control.

02

Circuit architecture

Two or more potentiometric or non-contact sensing tracks move from the same pedal mechanism but produce independent signals. Separate reference or low-reference circuits may be used to reduce common-cause failure.

03

Controller interpretation

The powertrain controller interprets correlated tracks as driver torque demand—not as a direct throttle cable position. Implausible correlation, missing reference voltage or an unsafe rate of change triggers reduced-power operation.

04

Normal response

Two or three smooth, correlated tracks. Stable rest and full-travel endpoints. No sudden disagreement between tracks.

05

System relationship

Judge the signal only under a defined operating condition. Verify its power, reference, ground, mechanical input and related scan data before deciding the sensing element is incorrect.

Common mistakes

AVOID THE
FALSE CLUE.

COMPLETE TEST SEQUENCE

  1. Verify powers and grounds shared by the pedal tracks.
  2. Graph all APP parameters on the scan tool.
  3. Depress and release the pedal slowly several times.
  4. Confirm each track is smooth and their ratio stays consistent.
DO NOT CONDEMN A SENSOR

until its power, ground, signal circuit, mechanical target and related system inputs have been verified.

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Diagnostic details

Purpose

APP sensors tell the electronic throttle system how much acceleration the driver is requesting.

Scan tool data

  • APP sensor 1
  • APP sensor 2
  • Commanded throttle
  • Actual throttle position

Failure symptoms

  • Reduced power
  • No throttle response
  • Intermittent throttle response

Related DTCs

  • P2122 – APP Circuit Low
  • P2123 – APP Circuit High
  • P2127 – APP Circuit Low
  • P2128 – APP Circuit High
  • P2138 – APP Correlation

Diagnostic tips

  • Compare all available APP signals.
  • Check shared reference and ground circuits.

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.

Potentiometer Position Sensor

A moving wiper changes the division of a reference voltage. Redundant tracks may share or have separate circuits.

Operating principle

  • A moving wiper changes the division of a reference voltage. Redundant tracks may share or have separate circuits.

Circuit identification

Application-specific; see wiring below

Wiring

  • Reference, low reference and wiper signals; count and track relationship vary.

Expected readings

  • Smooth repeatable travel without dropouts; redundant tracks maintain their specified relationship.

Multimeter testing

  • Graph all tracks during slow permitted travel. Check reference and low reference before diagnosing a worn track.

Oscilloscope setup

  • Identify the output interface and approved test points before connecting. Set the range, coupling and probes for that circuit.

Oscilloscope testing

  • Graph all tracks during slow permitted travel. Check reference and low reference before diagnosing a worn track.
  • Do not force an electronic throttle against its drive. Dual-track describes redundancy, not the sensing technology.

Waveform interpretation

Smooth repeatable travel without dropouts; redundant tracks maintain their specified relationship. No universal known-good waveform is specified for this design.

Common failures

  • Connection, supply or signal-path faults where applicable
  • Damage, installation error or loss of calibration appropriate to this design

Diagnostic tips

  • Do not force an electronic throttle against its drive. Dual-track describes redundancy, not the sensing technology.
  • Construction, output format and number of redundant channels are separate attributes.
Contactless Inductive Position Sensor

An excited coil system senses a conductive target without a sliding electrical contact.

Operating principle

  • An excited coil system senses a conductive target without a sliding electrical contact.

Circuit identification

Application-specific; see wiring below

Wiring

  • Powered electronics with application-specific analog or digital output.

Expected readings

  • Repeatable position data and correct redundant-channel correlation.

Multimeter testing

  • Verify power and ground, then compare channels throughout permitted travel. Decode the actual interface rather than testing internal coil resistance.

Oscilloscope setup

  • Identify the output interface and approved test points before connecting. Set the range, coupling and probes for that circuit.

Oscilloscope testing

  • Verify power and ground, then compare channels throughout permitted travel. Decode the actual interface rather than testing internal coil resistance.
  • An inductive target need not be a magnet. Confirm construction and interface from service information.

Waveform interpretation

Repeatable position data and correct redundant-channel correlation. No universal known-good waveform is specified for this design.

Common failures

  • Connection, supply or signal-path faults where applicable
  • Damage, installation error or loss of calibration appropriate to this design

Diagnostic tips

  • An inductive target need not be a magnet. Confirm construction and interface from service information.
  • Construction, output format and number of redundant channels are separate attributes.
Hall-Effect Position Sensor

A magnetic target changes the field measured by a powered Hall element.

Operating principle

  • A magnetic target changes the field measured by a powered Hall element.

Circuit identification

Application-specific; see wiring below

Wiring

  • Powered electronics; analog or digital channels depend on application.

Expected readings

  • Smooth position response with the specified channel relationship.

Multimeter testing

  • Check target alignment and graph redundant channels while moving through permitted travel.

Oscilloscope setup

  • Identify the output interface and approved test points before connecting. Set the range, coupling and probes for that circuit.

Oscilloscope testing

  • Check target alignment and graph redundant channels while moving through permitted travel.
  • Do not resistance-test powered sensor electronics or infer sensor type from wire count alone.

Waveform interpretation

Smooth position response with the specified channel relationship. No universal known-good waveform is specified for this design.

Common failures

  • Connection, supply or signal-path faults where applicable
  • Damage, installation error or loss of calibration appropriate to this design

Diagnostic tips

  • Do not resistance-test powered sensor electronics or infer sensor type from wire count alone.
  • Construction, output format and number of redundant channels are separate attributes.