Suspect a bad crankshaft position sensor?
The crankshaft position sensor relays engine speed and position to the Engine Control Unit (ECU). This vital information is critical to unlocking optimal performance, allowing the ECU to determine fuel injection and ignition timing precisely.
But how can you tell when this component malfunctions?
Buckle up as we delve into how to test crankshaft position sensor, prevent future problems, and keep your engine purring.
This Article Contains:
- How to Test a Crankshaft Position Sensor Step-By-Step
- 4 Critical Symptoms of a Failing Crankshaft Position Sensor
- What Causes a Crankshaft Position Sensor to Fail?
How to Test a Crankshaft Position Sensor Step-By-Step
When your check engine light is on, you should first use a diagnostic scan tool to read the engine code before diving in and replacing the crank position sensor (CKP sensor). Issues with the crankshaft position sensor generally display codes between P0335 and P0338.
If the trouble code is related to the CKP sensor, visually inspect the sensor for cracks, loose or corroded connector pins, and other signs of damage.
If everything looks good, try one of these tests.
Test 1: Crank Test
If you have a diagnostic tool capable of reading RPMs, attach it to the sensor and crank the engine. It should display an engine speed reading of between 100 and 500 RPM. Anything outside of this range can indicate a bad crankshaft position sensor.
If you don’t have a diagnostic tool, you can manually crank the engine by turning the crankshaft pulley bolt and listening for any irregularities. Any grinding, knocking, or scraping noise could indicate a problem with the CKP sensor or other engine components.
Note: Manual engine cranking has its limitations and should be done cautiously. Ensure you disconnect the battery to avoid accidental starting.
Test 2: Multimeter Test
Testing a failing sensor with a multimeter differs depending on the type of sensor your vehicle has. There are two main types of crankshaft position sensors:
Note: You can also test the cam sensor with a multimeter. However, accessing the cam sensor can require some disassembly.
A. Hall Effect Sensor
These sensors use a magnet and a Hall effect chip to generate a voltage signal as the crankshaft rotates. You’ll need a multimeter set to DC voltage to test this type of sensor.
Note: Hall effect sensors can either have two (2-wire crankshaft position sensor) or three wires (3-wire crank sensor). The steps below are for a “3-wire crank sensor.”
- Before starting, ensure the power is off. Consider disconnecting the battery or removing the fuel pump fuse to be safe. If your car has a distributor, you can unplug the center ignition cable and ground it to the engine using a jumper wire.
- Set the multimeter to DC voltage and the range to 20 volts. Connect the positive leads of the multimeter (red) to the power supply pin of the Hall effect Sensor. Connect the negative (black) to the sensor’s ground pin.
- Enable the power sources you disconnected. This can include undoing anything done in step 1. For example, reconnecting the battery, fuel pump fuse, or ignition cable (also removing the jumper wire).
- The multimeter should display the voltage level. Hall effect sensors commonly operate around 5 and 13 volts but can vary depending on the sensor’s specifications.
- If the multimeter reading differs significantly from the expected voltage, you may have a failing sensor. In this case, it’s best to call a mechanic.
B. Variable Reluctance Sensor
These sensors use a permanent magnet and a coil to generate a voltage signal as the crankshaft rotates. To test this sensor, you can try a resistance test:
- Ensure the car is off or disconnect the battery before beginning.
- Set the multimeter to ohms. This CKP sensor should have about 200 to 2,000 ohms of resistance, so set the multimeter to 20,000 ohms.
- Connect the multimeter’s leads to the CKP sensor.
- If the multimeter reading is within normal range, your crank position sensor is likely fine.
It’s also a good idea to check the sensor wire and wiring harness while testing any type of sensor. An exposed sensor wire or loose wiring harness can cause an intermittent signal. And, if you’re still experiencing engine trouble, it’s best to let a mechanic handle it.
Note: Although unlikely, it’s possible the CKP sensor issue could be caused by the reluctor ring. The reluctor ring is a toothed wheel that attaches to the crankshaft. The best way to check this is through a visual inspection.
Now, before a faulty sensor fails completely, it often throws out clues. Recognizing these early warning signs can save you time and money.
4 Critical Symptoms of a Failing Crankshaft Position Sensor
From rough idling to not starting, these signs can point to a bad crank sensor:
- Lit check engine light: When the powertrain control module (PCM) or the ECU detects a fault in the crank sensor, it activates the check engine light and stores a specific code.
- Engine won’t start: Without the signal from the crankshaft sensor, the engine control unit may not be able to determine the engine’s position for fuel injection. This can lead to issues with ignition timing and starting.
- Engine running rough or misfiring: A faulty sensor can affect timing by sending incorrect information. The spark plugs can fall victim to misfires and incomplete combustion, leaving the engine running rough, vibrating, and hesitant.
- Reduced fuel efficiency: A faulty sensor can throw the entire combustion process, including the spark plug and ignition timing, out of whack. This can affect the fuel pressure as it leads to either excessive fuel injection or fuel being injected at the wrong time.
Note: In addition to a faulty crankshaft position sensor, these symptoms can also suggest problems with the camshaft position sensor or the ignition and fuel system.
Sure, catching a bad crankshaft position sensor early on saves you the hassle. But knowing what causes a bad crank sensor can help stop it from happening again.
What Causes a Crankshaft Position Sensor to Fail?
The factors that can cause crank sensor failure include:
- Wear and tear: The crankshaft sensor can fail with time since it’s exposed to constant engine heat and vibrations.
- Overheating engine: If the engine overheats, it can melt the plastic covering and damage the crankshaft position sensor.
- Moisture and corrosion: Moisture can build inside the sensor’s housing or connector, causing it to erode with time. The corrosion can disrupt the signals, leading to incorrect readings or complete sensor failure.
- Broken timing belt: A broken timing belt can throw a crankshaft and camshaft sensor out of sync. This can confuse the ECU and lead to poor combustion.
Note: The same causes could also lead to a faulty camshaft position sensor, causing it to display similar symptoms to a bad CKP.
Eliminate the Guesswork with AutoNation Mobile Service
Without the crank sensor, your car can run into serious problems, like engine cranking or failing to start altogether.
Why test a faulty sensor yourself when you can leave it to a professional?
AutoNation Mobile Service brings the expertise to your driveway.
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