How to Test a 3-wire Cam with a Multimeter

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Have you ever noticed unstable idle, stalling on acceleration and bucking in your car? Well, this could be an issue with your Camshaft Position Sensor.

A cam is fastened to the shaft to form the integral part of the camshaft. The movements of a camshaft in a rotational motion determines the opening and closing of the valves.

Opening and closing of valves in the engine system, enhances fuel to enter and the exhaust to exit out of each cylinder. Therefore, it is essential to have the perfect timing of the camshaft movements.

The camshaft fitted with a sensor communicates to the engine computer on when to release fuel from the injector to ensure it happens at the same time the camshaft opens the intake valve.

The Camshaft Position Sensor, commonly abbreviated as CMP, gives camshaft position information by use of the Powertrain Control Module to enhance fuel synchronization.

When using engines fitted with 3-wire sensors, the CMP variably hesitates the sensor. The highest mark on the camshaft projections prompts the CMP hesitating the sensor. The distributor engine utilizes the conventional distributor fitted with Hall Effect transistor.

The three-wire cam uses a unique Hall Effect device.

A tiny current flow through the coil causes the contact to trip, thus turning on a large circuit. A real small current streaming from terminal one to terminal two allows a real high current flow from terminal one to terminal three. While using the Hall effect transistor, the tiny current is not applicable.

Instead, there is the ignition of the high-current path by the magnetic fields. The magnetic fields could arise from a magnet fitted in the rotating part under the sensor or from a notch already disturbing the sensor.

​How to Test a 3- Wire Sensor

  1. Locate the ground, the power, and the signal wires using your car’s repair manual. Set your multimeter to DC volts to test the sensor’s circuit.
  2. Turn the ignition key on, but let the engine stay OFF.
  3. Touch the black cable on your multimeter to the ground and the other probe cable to touch the power wire.
  4. Check the readings on the multimeter and compare them with the manual’s specification.
  5. Let your helper start your car’s engine.
  6. Touch the ground wire with the black cable and the signal wire with the red probe.
  7. Check your readings and compare them with your car’s manual’s specifications.
  8. In case the voltage reading is lower than the specification of your car, or the absence of any signal from your vehicle, there are high chances that the sensor is faulty.
  9. Uninstall the sensor and diagnose it for symptoms of physical damage.

What are the signs of a faulty CMP? These symptoms include intermittent rough running, hesitation, bucking, unstable idle, prolonged crank time on a cold engine, stalling on acceleration, stumble, and lousy fuel budget.

Stay calm as we explore ten steps on…

​How to Diagnose the CMP Sensor Using 3-Wire Sensors

  1. Switch off your car
  2. Disconnect the Camshaft Position Sensor
  3. Put the power on, with the engine off
  4. Measure the circuit between the terminals and sensor connector using an appropriate multimeter
  5. Check the readings. In case the multimeter reads a voltage of 10.5 and above, then the CMP sensor is in good condition. If the multimeter reads otherwise, continue to the next steps.
  6. Turn off the ignition.
  7. Fix a cut-out box in between the PCM and CMP
  8. Scale the monitor of your multimeter to a scale below a voltage of 5
  9. Test the volts between cut-out-box terminals with the engine running at varying RPM
  10. Check the reading. In case the volts change above 0.1 volts, the sensor is good. If the reading is otherwise, then your sensor is faulty.

If you are the Do-It-Yourself type of a person, then you can consider replacing the Camshaft Position Sensor. But how do you go about it? Here are simple steps to go about the process.

(CAUTION! Before detaching the CMP sensor, set the cylinders from number 1 to 10 After Top Dead Corner of the thumb stroke. Master the arrangements of the sensor’s electrical connection so that you make sure it remains the same after the installation.)

  • Place the cylinder number 1 at 10 degrees After Top Dead Center
  • Match the CMP sensor terminal connector with the engine assembly
  • Detach the camshaft position sensor maintaining the sensors and the screws
  • Disconnect the holding bolt and retaining down clamp
  • Remove the oil transitional pump tube together with the camshaft sensor casing.
  • Detach the CMP sensor casing from the covering of the front engine.

After removing the existing and faulty Camshaft Position Sensor, here is how to go about installing a new one.

  1. Locate the plastic cover attached to the new crankshaft sensor. The plastic cover should be in contact with the top surface of the camshaft sensor housing.
  2. Change the oil pump shaft from the previous camshaft position to the new sensor housing.
  3. Fix the camshaft housing to ensure that the gear interaction happens when the locator’s tool pointer is pointing 30 degrees anticlockwise.
  4. Make sure there is an alignment of the sensor terminal connection with its match points.
  5. Connect the hold-down bolt and clamp and tighten the bolt properly.
  6. Remove the sensor casing and repeat the above procedure from the first step.
  7. Fix the sensor retaining the screws.
  8. Tighten the screws to 2-4 Nm
  9. Connect the engine control sensor wiring to the sensor.
  10. Attach the starter coil, radio starter capacitor, and starter coil bracket.
  11. Fix back the black battery lead.

The 3-wire sensor is applicable when the car’s computer requires a constant 5.0 voltage, and the produced signal is tiny and needs to be amplified for it to be of use. These signals are subject to be affected by interference from radiation signals. The current flowing via the spark plug radiates out to other wires nearby. Therefore, it is always advisable to put wiring harnesses back to where they belong.

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