Engine position / CMP

CAMSHAFT POSITION SENSOR

Reports camshaft phase so the control module can identify cylinder position and synchronize sequential injection and variable valve timing.

FIELD GUIDE02/13

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 / DIGITAL

Hall-Effect CMP

Usually 3 wires: supply, ground and signal

Produces a square-wave window pattern supplied by the controller.

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

+ Load-test supply and ground.

+ Scope CMP with CKP on a second channel.

+ Verify every edge repeats at the same crank position.

EXPECTED

✓ Full logic-level switching

✓ Stable phase relationship

✓ No extra or missing edges

COMMON FAULTS

— Stuck logic level

— Mechanical timing shift

— Poor sensor ground

TYPE 02PASSIVE / ANALOG

Inductive CMP

Usually 2 wires, sometimes shielded

Self-generates a bipolar AC pattern; output depends on target speed and air gap.

Reading the signal

Good waveform

A passive variable-reluctance pickup produces an alternating signal as the target moves. Amplitude generally increases with speed, and tooth spacing or index features repeat consistently at a steady speed.

Faulty waveform

Weak output during cranking, recurring distorted teeth or random dropouts can arise from excessive air gap, target damage, wiring or the pickup. Compare at the same speed and polarity; a low-speed trace should not be judged against a high-speed amplitude.

TYPE-SPECIFIC TESTS

+ Scope across the two signal wires.

+ Check amplitude during cranking, not only at idle.

+ Compare the complete pattern against CKP timing.

EXPECTED

✓ Bipolar AC pattern

✓ Repeatable lobe spacing

✓ Adequate cranking amplitude

COMMON FAULTS

— Low cranking amplitude

— Open winding

— Target or air-gap damage

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

Reports camshaft phase so the control module can identify cylinder position and synchronize sequential injection and variable valve timing.

02

Circuit architecture

Hall and magnetoresistive designs use a powered semiconductor element; some older applications use a variable-reluctance pickup. A target wheel or patterned cam feature changes the output as the cam rotates.

03

Controller interpretation

The controller compares cam edges with the crank reference to identify compression stroke, schedule sequential injection and measure commanded phaser movement. The relationship—not a generic edge position—is the important evidence.

04

Normal response

Square-wave Hall signal on most modern applications. Pattern repeats once or several times per cam revolution. Edges remain aligned with the CKP reference on every cycle.

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 reference voltage or battery feed and sensor ground.
  2. Capture the signal during cranking and at idle.
  3. Use a second channel on CKP to check cam-to-crank correlation.
  4. Inspect for repeatable edges and a stable phase relationship.
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

CMP information helps identify engine phase and supports sequential injection, ignition, variable valve timing and synchronization.

Scan tool data

  • CMP position
  • Desired cam angle
  • Actual cam angle
  • CKP/CMP synchronization
  • VVT data

Failure symptoms

  • Extended cranking
  • No-start on some applications
  • Poor performance
  • VVT faults
  • Correlation DTCs

Related DTCs

  • P0340 – CMP Sensor A Circuit
  • P0341 – CMP Range/Performance
  • P0342 – CMP Circuit Low
  • P0343 – CMP Circuit High
  • P0344 – CMP Circuit Intermittent

Diagnostic tips

  • Do not overlook mechanical timing.
  • Compare CMP and CKP waveforms for correlation diagnosis.

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 camshaft position sensor.

Operating principle

  • A target alters the magnetic field at the Hall element.
  • Sensor electronics produce a digital signal.

Circuit identification

Typically 3 wires

Expected readings

  • Signal switches between defined voltage states.
  • Pattern must remain correctly synchronized with CKP.

Multimeter testing

  • Verify power.
  • Verify ground.
  • Check signal switching.

Oscilloscope setup

  • DC coupling
  • Monitor CMP signal
  • Use CKP on another channel for correlation testing

Oscilloscope testing

  • Look for clean transitions.
  • Compare CMP against CKP.
  • Check for intermittent dropout.

Waveform interpretation

Typical Hall-effect CMP digital waveform.

Common failures

  • Circuit fault
  • Internal sensor failure
  • Target damage

Diagnostic tips

  • A good-looking CMP waveform can still be incorrectly timed relative to CKP.
Variable Reluctance

Passive magnetic camshaft position sensor.

Operating principle

  • Target movement changes magnetic flux.
  • The sensor generates AC voltage.

Circuit identification

Typically 2 wires

Wiring

  • Signal positive
  • Signal negative

Expected readings

  • AC signal amplitude varies with speed.

Multimeter testing

  • Check resistance only when specified.
  • Check AC output when appropriate.

Oscilloscope setup

  • AC coupling can be useful.
  • Monitor CMP and CKP simultaneously for correlation.

Oscilloscope testing

  • Check waveform consistency.
  • Compare phase relationship with CKP.

Waveform interpretation

Typical passive variable-reluctance CMP waveform.

Common failures

  • Excessive air gap
  • Target damage

Diagnostic tips

  • Use correlation data rather than judging the CMP waveform in isolation.