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Camshaft Position Sensor (CMP): Understanding The Structure, Symptoms, Maintenance, And Costs

By R&D
Published on December 21st, 2023

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Elimination of the distributor in modern vehicles created the need for an alternate means of monitoring engine RPM and crankshaft position, determining the correct spark plug firing sequence, and controlling fuel injector and ignition timing. These functions are facilitated by the crankshaft and/or camshaft position sensor.

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The Camshaft of the Engine

Overview of the Camshaft Position Sensor (CMP):

The crankshaft and camshaft position sensors monitor the speed of the crankshaft or camshaft, and supply a series of high- and low-voltage pulses which represent the speed of rotation to the vehicle’s Engine Control Module (ECM). The frequency of voltage pulses increases as crankshaft/camshaft rpm increases. Sensors of this type offer the added benefit of eliminating ignition timing variations due to wear and/or backlash in the timing chain and distributor gear, as well as eliminating the need for timing adjustments.

The ECM uses these signals primarily for spark timing or fuel injector control. On OBDII-compliant vehicles, the crankshaft position sensor also serves to detect variations in crankshaft speed caused by ignition misfire. If these variations are significant or frequent enough, the ECM stores a Diagnostic Trouble Code (DTC) and illuminates the Malfunction Indicator Lamp (MIL).

Common Symptoms of a Faulty Camshaft Position Sensor:

Some common symptoms of a faulty camshaft position sensor are listed below. Be aware that these symptoms can occur due to various reasons, such as faulty sensor wiring, magnetic interference, worn internal components, or sensor circuitry malfunction.

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a. Difficulty Starting the Engine: If the CMP is faulty, it can result in starting problems that may be intermittent or prolonged. This happens because the ECM receives incorrect timing information.

b. Rough Idling or Stalling: Inaccurate camshaft position data can cause issues such as irregular idle, engine misfire, and sudden stalling during driving.

c. Reduced Power and Acceleration: If the CMP is not functioning properly, it can cause a disturbance in the timing of fuel injection and ignition, which can result in reduced engine performance and slow acceleration.

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d. Malfunction Indicator Lamp (MIL): If an issue with the CMP is present, the ECM can often detect inconsistencies in the camshaft position data and activate the MIL.

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Maintenance Tips:

The CMP is constructed to last for the life of the car, and there is no set maintenance schedule for CMP replacement. The sensor is only replaced when it is damaged or defective. However, regular maintenance will help extend the lifespan of your vehicle’s CMP. Recommended maintenance actions include:

a. Keep Engine Clean: A buildup of engine dirt and debris can cause voltage fluctuations in the sensor, leading to damage over time.

b. Inspect Wiring: Check the wiring and connector of the CMP sensor for any looseness or damage.

c. Keep Oil Clean: Operating an engine with dirty or old oil can result in premature wear of engine components, including the CMP sensor.

To ensure optimal engine performance and reliability, it is important to maintain the CMP. Here are some helpful maintenance tips to keep the CMP in good condition:

a. Regular Inspections: Make sure to conduct routine inspections on the wiring harness and connector of the CMP for any indications of damage, corrosion, or loose connections. If problems are observed, take immediate action to prevent further damage.

b. Keep CMP Clean: Regularly clean the vicinity of the CMP to avoid the accumulation of dirt, debris, or oil, which may negatively affect the sensor's functionality or result in incorrect readings.

Cost of Camshaft Position Sensor:

The price of a camshaft position sensor can vary based on a number of factors including the vehicle’s make and model, the sensor brand, and the source of purchase. Additionally, prices may differ between suppliers or retailers, making it difficult to obrain an accurate cost estimate without detailed information.

The cost of a camshaft position sensor typically varies between $20 and $100. However, if you opt for premium or OEM sensors, the price may go beyond $100. It's crucial to make sure that the replacement sensor is suitable for your vehicle model and meets the necessary quality standards.


To ensure precise engine operation and performance, the Camshaft Position Sensor (CMP) plays a crucial role. It is important for vehicle owners and technicians to have knowledge of its structure, symptoms of failure, and testing/replacement procedures. This enables accurate diagnosis of engine issues and the maintenance of engine health. Faulty CMPs should be promptly replaced to maintain optimal engine performance, fuel efficiency, and longevity, resulting in a smoother driving experience. Regular maintenance also contributes to the longevity of the engine.

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