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Crankshaft Position Sensor (Crank Sensor / CKP)

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Last Updated on: 16th November 2023, 01:54 am

The Crankshaft Position Sensor (CPS / CKP), is an often overlooked, important sensor in modern vehicles. This small sensor monitors the position and speed of the crankshaft.

It feeds critical data to the vehicle’s computer, optimising performance and efficiency and allowing the smooth operation of the engine.

In this article, we’ll delve into the details of what a crankshaft position sensor is, how it functions, and its importance.

What Is the Crankshaft Position Sensor

An electric device known as the crankshaft position sensor, or simply crank sensor (CKP), is employed in internal combustion engines (both petrol and diesel).

Its primary role is to monitor the location and rotational velocity of the crankshaft.

crankshaft position sensor diagram

The placement of the crankshaft position sensor is such that the sensor tip brushes past the teeth on a reluctor ring that is attached to the crankshaft.

The reluctor ring, missing one or more teeth, serves as a reference point for the crankshaft’s position to the engine computer (PCM).

As the crankshaft rotates, the sensor produces a voltage signal in pulses, each of which corresponds to a tooth on the reluctor ring.

  • This data is used by the engine control unit (ECU) to manage the ignition system’s timing, fuel injection, and other engine operations.
  • When used in conjunction with the camshaft position sensor, the crankshaft position sensor helps synchronize the engine and maintain its smooth operation.

For engines with variable valve timing, this synchronization is of utmost importance.

When a four-stroke engine is ignited, the crankshaft sensor provides the ECU with necessary information about when to inject fuel.

By providing a reference point for fuel injection and ignition timing, crankshaft sensors help optimize engine performance and operation.

The crankshaft position sensor is commonly used as the primary reference for determining the engine’s speed in revolutions per minute (RPM).

Before the advent of electronic crank sensors, petrol engines relied on manually adjusting the distributor to a timing mark.

various types of crankshaft position sensors

Types

Crankshaft position sensors come in several forms, including the following.

  1. Inductive sensor
  2. Hall Effect sensor
  3. Magnetoresistive sensor
  4. Optical sensor

Among these, inductive sensors are the simplest and entirely passive electronics.

Compared to inductive sensors, Hall effect and magnetoresistive sensors can detect static (unchanging) magnetic fields. Though not very durable, optical sensors can provide the most accurate detection.

Pick-up coil type sensors often feature a two-pin connection, while the Hall-effect sensor uses a three-pin connection (reference voltage, ground, and signal).

A design feature seen in “three-wire” inductive crank sensors is the third wire, essentially a co-axial shield that prevents the two primary sensor wires from picking up stray electrical pulses within the car engine compartment.

Sensor Placement

Common installation points include the following.

  • the primary crank pulley
  • the flywheel
  • the camshaft
  • the crankshaft

Usually, crankshaft position sensors are found at the base of the engine (primary crank pulley, flywheel, and crankshaft) or near the top of the engine by the timing cover (camshaft).

They have a distinctive appearance different from other sensors.

> Where to find the crankshaft position sensor

appearance of crankshaft sensor highlighted in red

What Happens When a Crankshaft Position Sensor Fails

A faulty crank sensor can lead to various symptoms, such as the engine failing to start or cutting out while running.

This is because diesel engines’ fuel injection or petrol engines’ spark ignition is often timed based on the crank sensor’s position signal.

When it malfunctions, it stops sending the vital information needed for ignition and other system components.

A faulty sensor may cause:

  • Check engine light (CEL) activation
  • Declining engine performance
  • Deteriorating fuel efficiency
  • Difficulty in starting the engine
  • Rough idle and increased vibrations
  • Shuddering, shaking, and jerking
  • Stalling
  • Misfiring

The sensor also feeds speed information to the engine speed gauge (RPM), which could lead to minor shifts in RPMs or deviations from expected values.

A common OBD fault code associated with the crankshaft position sensor is the P0335 code. You should always scan the car with a reputable OBD scanner to further diagnose this issue.

Reasons for Sensor Failure

Common reasons for sensor failure include burning out, wearing out, or simple failure after high mileage (typically over 80,000 miles).

Factors such as exposure to heat (from an overheating engine), rust on connector pins, or wire damage due to vibration can cause the sensor to fail.

Many modern crankshaft sensors are sealed, thus water or other liquids cannot affect them.

If a crankshaft position sensor is replaced, it should be relearned to avoid potential issues.

Starting a Car with a Malfunctioning Crankshaft Sensor

When the crankshaft sensor is not functioning properly, the vehicle may not start.

The reason is that the sensor sends signals about the crankshaft’s position and speed to the ECU, which are critical for proper ignition timing and fuel injection.

Without these signals, the engine might struggle to start or stall shortly after starting.

However, there are cases where a car might start even with a faulty sensor if the damage is partial and it can still send some signals to the ECU.

This could allow the car to start and run briefly, but it might stall or exhibit reduced performance and fuel efficiency.

There may be ways to start a car with a faulty crankshaft sensor or temporarily fix it, but it’s always advisable to replace a malfunctioning sensor.

Consequences of Not Repairing a Faulty Sensor

Neglecting to fix a faulty crankshaft sensor can have severe repercussions for your vehicle.

The sensor plays a crucial role in the engine’s proper functioning, and a malfunctioning one can lead to a range of performance and reliability issues.

Unattended, a faulty crankshaft sensor could even cause engine damage if the vehicle is continuously driven.

Ignoring a faulty crankshaft sensor could lead to a vehicle breakdown. Besides being inconvenient, this could be hazardous if you’re stuck in a remote location or on a busy roadway.

Moreover, it might be illegal to drive a vehicle with a failing crankshaft sensor due to increased emissions.

If the sensor isn’t working properly, the engine might run less efficiently, causing higher emissions that could violate emissions regulations.

To prevent these issues and ensure your vehicle’s safe and reliable operation, it’s crucial to address any problems with the crankshaft sensor immediately and replace it if necessary.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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