Camshaft Position Sensor Test

Camshaft position sensor symptoms can manifest in various ways and may include:

• No power
• Stalling
• Poor gas mileage
• Poor acceleration
• Rough idle
• Stumbling
• Hard to start
• No-start condition
• Misfires
• Transmission may feel slow

Depending on your particular vehicle model, the ECM (electronic control module or car computer) may use the CMP sensor to synchronize and sequence fuel injectors and/or set direct ignition timing.

However, these symptoms are not exclusive of a bad or failing CMP sensor. Furthermore, depending on the particular fault and vehicle model, one or more of these symptoms may be present. If a failing sensor meets the enable criteria programmed into the car's computer, the fault will trigger the Check Engine Light (CEL).

So you won't necessarily see the CEL turn on. Even if the engine light comes on and you retrieve a CMP sensor fault trouble code, it's a good idea to test the sensor to make sure you are dealing with a faulty component, a fault in the wire or connector or a related component.

The next sections will help you test your CMP sensor. You may want to have the vehicle repair manual for your particular vehicle make and model. The manual gives you the electrical value specifications, specific tests you may run for your sensor, help you identify wires and locate the sensor, if necessary.

If you don't have a copy of the manual yet, you can buy a relatively inexpensive copy through Amazon. Haynes manuals come with step-by-step procedures and images for many maintenance, troubleshooting and component replacement projects.

I. Camshaft Sensor Types

In general, you can find two types of camshaft position sensors:

• Magnetic type or variable reluctance: Usually, you can identify this type of sensor because of its two wires. The magnetic type produces its own voltage, an alternating current (AC) sine wave signal.
• Hall effect type: This type can be identified by its three wires, one for its reference signal or power, another for its ground, and a third one for a signal voltage sent to the computer.

Make sure you know what type of sensor you have in your system. On some models a magnetic type may have a third, shielded wire used to cancel noise. If necessary, consult your vehicle repair manual.

II. Camshaft Sensor Location

Broadly speaking, you'll find the sensor on top of the engine, on the left side of the valve cover or the front of the engine right by the camshaft sprocket.

Also, keep in mind that, depending on your particular model, you may have more than one CMP sensor. Your vehicle repair manual will help you locate and identify the sensor, if necessary.

III. Camshaft Position Sensor Visual Inspection

Before testing the sensor or circuit wires, make a visual inspection. Damage or contamination of a sensor or wiring can prevent a CMP sensor from sending the required signal to the computer.

Check the connector for:

• rust
• contamination
• damage
• loose wires

Check the wires for:

• breaks
• burns
• looseness

And, depending on the sensor location and accessibility, decide how your are going to test the sensor.

When testing the CMP sensor:

Back probe the CMP sensor, if at all possible, to prevent damage to the sensor, wires or connector.

Another alternative is to unplug the sensor and place a copper strand on each terminal pin and then plug the connector back. Use the strands of copper sticking out of the connector as DMM connecting points during your tests.

If none of these alternatives is possible, you may pierce the sensor wires with a pin. Just make sure to repair the pierced points with electrical tape to prevent corrosion from creeping under the insulation and damaging the wires.

IV. Camshaft Position Sensor Test

Usually, the CMP sensor signal has a low frequency at idle that a fairly decent DMM is able to read both sides of the wave. So, you may see the measured voltage signal fluctuating on your DMM display.

Testing a Magnetic type CMP Sensor

Magnetic type CMP sensors produce their own AC (sine wave) signal. You'll need a digital multimeter (DMM) that can test for AC (alternating current) voltage.

1. Disable the ignition or fuel system to prevent the engine from starting. For this, disconnect the ignition coil, high tension wire from the distributor cap and ground the wire with a jumping wire to the engine block. You can use a metal bracket or bolt on the engine for this. Another way to prevent the engine from starting is to remove the fuel pump fuse. if necessary, consult your vehicle repair manual,
2. Set the transmission to Park (automatic) or Neutral (manual).
3. Engage the emergency brakes.
4. Unplug the CMP sensor.
5. Set your multimeter to DC voltage.
6. Check for voltage at the harness connector with the ignition On, engine Off. Depending on your particular model, you may find around 1.5 volts at the terminal. Consult your vehicle repair manual.
7. Now set your DMM meter to read AC voltage.
8. Connect your DMM leads to the sensor terminal pins.
9. Have an assistant crank the engine for a few seconds.
10. Read the voltage displayed on your multimeter.
11. Compare your results to your repair manual specifications.

Camshaft position sensor resistance test

You can also measure your CMP sensor resistance. Look up the resistance value for your sensor in your vehicle repair manual.

Set your multimeter to Ohms and touch your meter leads to the sensor terminal pins. If there is infinite resistance, the sensor is open and you need to replace it. On some models, you'll get a resistance value between 200 and 900 ohms. Consult your repair manual specifications.

Camshaft position sensor bench test

If you have easy access to the CMP sensor and can remove it from the vehicle, you can bench test the sensor as well.

Set your DMM to AC volts and connect the meter leads to the sensor connector pins.

Pass a metal object, a blade for example, in front of and close to the sensor's magnet. You should see a pulsing voltage signal every time you pass the object in front of the magnet; otherwise, the sensor is not working.

Testing a Hall Effect Type CMP Sensor

A Hall effect sensor produces a squared, digital signal, representing the highest and lowest voltage points.

1. Set your transmission to Park (automatic) or Neutral (manual).
2. Engage the emergency brakes.
3. Remove the fuel pump fuse to prevent the engine from starting. If necessary, consult your vehicle repair manual.
4. Set your DMM to DC volts.
5. Back probe the power wire on the harness connector with your DMM's red lead, and connect your DMM's ground (black) lead to battery negative, the post with the negative (-) sign next to it.
6. Have an assistant crank the engine for a few seconds.
7. You should get a DMM readout of about 5 volts.
8. Now, back probe the ground wire on the harness connector with your DMM's red lead. Leave your DMM's ground (black) lead connected to battery negative.
9. Have an assistant crank the engine for a few seconds.
10. You should get a voltage reading of about 0.1 or 0.2 volts.
11. Now, back probe the signal wire on the harness connector with your DMM's red lead. Leave your DMM's ground (black) lead connected to battery negative.
12. Have an assistant crank the engine for a few seconds.
13. You should get a fluctuating voltage reading between 0 and 5 volts.

If your signal values seems to be off the mark, but power and ground values are OK, replace the CMP sensor. Consult your vehicle repair manual for the electrical value specifications for your particular model, if necessary.

V. Camshaft Position Sensor Codes

Often, a problem with the camshaft position sensor, or its circuit, will trigger the check engine light. In this case, you'll find one or more diagnostic trouble codes (DTC) associated with this sensor. These codes may include one or more of the following:

P0340. This code may indicate

• a problem with the CMP sensor itself
• damaged or loose wire
• a problem with the reluctor wheel
• timing component problem
• ECU (car computer) issue

P0341:

• bad CMP sensor
• faulty wire connection
• damaged reluctor wheel
• wiring too close to spark plug wiring (interference)

P0342:

• bad CMP sensor
• faulty connection or harness problem
• faulty starter or circuit
• battery issue

P0343:

• bad CMP sensor
• faulty ground or signal wiring
• power wire shorted

P0344:

• opened or shorted power wiring
• faulty ground or signal wiring
• signal wiring shorted to ground or power
• reluctor wheel issue
• crankshaft sensor intermittent signal

P1340:

• bad CMP sensor
• harness open or shorted
• faulty connection
• starting system issue
• no battery power

P1341:

• faulty cmp sensor
• bad spark plug or coil
• ignition coil harness or circuit problem
• vacuum leak problem

VI. Camshaft Position Sensor Replacement

Usually, replacing the CMP sensor is a straightforward operation. Depending on your particular vehicle model, you may need to remove one or more components to gain access to the sensor. Then, unscrew one or two mounting bolts and remove it.

Match the new sensor to the old one to make sure you got the correct replacement and install it.

If necessary, consult your vehicle repair manual.

VII. What If My CMP Sensor Tests OK?

If you didn't find anything wrong with your CMP sensor, connector or wiring, don't forget to check your timing belt or chain, specially if you haven't replaced the belt in five years or more. A loose, overstretched, faulty belt, chain or related component will prevent the sensor from doing its job.

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.