Driving with a faulty crankshaft position sensor can have grave consequences for your engine’s longevity, but you may not recognize the symptoms of a defective sensor unless one or more triggers the check engine light. Use the guide below to explore eight common symptoms of a faulty crankshaft position sensor and discover targeted diagnostic tips that help technicians detect failures early, saving time. For specific replacement part numbers and critical brand-specific procedures, trust Identifix Direct-Hit®’s extensive database of make-and-model-specific repair guides.
The Crankshaft Position Sensor’s Role in Engine Performance
Also known as the crank position sensor or engine speed sensor, the crankshaft position sensor provides the engine control module (ECM) with critical information about the crankshaft’s position and rotational speed (RPMs), enabling the ECM to control spark, fuel injection, and timing. The sensor’s location varies across automotive manufacturers, but it is often found near the flywheel, harmonic balancer, or the bottom side of the engine block. Most crankshaft position sensors last anywhere from 50,000 to 100,000 miles under normal operating conditions.
A crankshaft position sensor relays vital information to the ECM with the help of a harmonic balancer or crankshaft pulley. As the crankshaft spins, the crankshaft position sensor generates a magnetic pulse as it interacts with a notched reductor ring mounted on the harmonic balancer. The ECM requires continuous input from the crankshaft position sensor to modulate engine parameters accordingly.
Crankshaft position sensors typically fall into one of two categories: magnetic or Hall effect. More commonly on older vehicles, magnetic crankshaft position sensors feature a coil of wire wrapped around a magnetic core that generates a sine wave, the voltage and frequency of which increase as the engine speed rises. Modern vehicles feature Hall effect crankshaft position sensors, which output a square wave (on/off) and modulate voltage as they react to magnetic field changes.
8 Crankshaft Position Sensor Symptoms to Look For
Vehicles with faulty crankshaft position sensors exhibit one or more symptoms, eight of which we’ve listed below. Each of these symptoms alone is cause for concern and further investigation. However, getting to the bottom of faulty crankshaft position sensors can require more detective diagnostic work than you might think—unless you have Identifix Direct-Hit and Direct-Hit Mobile to rely on.
1. Check Engine Light
A faulty crankshaft position sensor can trigger a check engine light that corresponds to numerous codes, including the following:
The ECM often throws these codes when it receives inconsistent or out-of-range signals, or no signal at all from the crankshaft position sensor. Verify a solid, clean connection by inspecting electrical wires and connectors for loose connections or damage. Freeze-frame data may also show a sharp decline in engine speed each time the crankshaft position sensor falters.
2. Hard Starts
A faulty crankshaft position sensor that fails to signal the ECM can cause hard starts based on an improper air-fuel mixture. This lack of communication forces the ECM to guess when managing the ignition and fueling systems, which may result in the engine failing to start altogether or starting abruptly if it somehow gets the ratio correct. Technicians will observe a lack of fuel pulse, spark timing, and RPMs when the engine cranks but fails to receive the critical data necessary to fire.
For two-wire crankshaft sensors, begin by testing the continuity and voltage using a multimeter. The continuity should be somewhere between 200 and 1,000 ohms. The voltage should spike when a metal object passes over a working sensor.
Using a multimeter, verify that a three-wire crankshaft position sensor has adequate power and ground by measuring voltage and ohms, respectively. To test the signal wire, backprobe it, set the multimeter to volts, turn the key to the “run” position, and observe the voltage. As you crank the engine, the voltage should vary significantly; if not, it’s likely time to replace the sensor completely or investigate a more extensive wiring issue.
3. Random Stalls
A sudden drop in engine speed typically occurs before it stalls due to a failing crankshaft position sensor. Intermittent signal loss prevents the ECM from initiating a spark or injecting fuel. Before taking the vehicle on a test drive to monitor the crankshaft and camshaft signals, inspect any wiring near heat and vibration sources to rule out electrical damage.
4. Erratic RPMs
Erratic engine speed often causes the ECM to store misfire codes based on distorted signals stemming from the crankshaft position sensor. Verify engine speed on the live data feed and be on the lookout for other inconsistencies. Inspect the sensor itself to determine if any dirt or debris is physically preventing a clean signal transfer.
5. Misfire Codes
A defective crankshaft position sensor can also cause poor ignition timing and fuel delivery. Rule out the ignition and fueling systems before verifying that this symptom stems from the crankshaft position sensor. A wide discrepancy in fuel trim values and misfire conditions correlated with engine speed drops often indicate a defective sensor.
6. Reduced Fuel Economy
Incomplete or irregular combustion can greatly reduce fuel economy. Verify the crankshaft position sensor’s accuracy under various loads by taking a test drive and monitoring the long-term fuel trims. Compare the crankshaft position sensor readings to those of the camshaft.
7. Engine Vibrations
Discrepancies in the air/fuel mixture can also cause rough idling and engine vibrations based on inaccurate and intermittent sensor signals. Rule out a damaged harmonic balancer and check for high counts of stored misfire codes.
8. Foul-Smelling Exhaust
High fuel trims, resulting from inconsistent sensor signals, can cause unburned fuel to exit the exhaust. In addition to emitting a foul-smelling odor, this unburned fuel can also significantly reduce the catalytic converter’s lifespan. Monitor oxygen sensor readings, timing errors, and spark loss.
Comprehensive, Model-Specific Data You Can Rely On
Identifying a faulty crankshaft position sensor as the root cause of the symptoms listed above can require some detective work, but it’s well worth the effort when it comes to maintaining efficiency and productivity. Streamline this and other diagnostics and repair processes with Identifix, using our Direct-Hit auto repair software to access make-and-model repair guides for in-depth replacement procedures and specific part numbers. Contact us to learn how you can transform complex diagnostic problems into streamlined repairs and solutions that enhance your bottom line. Did you like this article? Find more great content at identifx.com/blogs and solera.com/blog.
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