When your car starts acting up, the crankshaft position sensor isn’t usually the first thing that comes to mind—but it should be high on the list. This small but essential sensor is crucial in keeping your engine running smoothly. From hard starts to unexpected stalling, a faulty crank sensor can cause headaches that leave you stranded at the worst possible moment.
In this post, we’ll break down the most common symptoms of a bad crank sensor, why it fails, and how to diagnose the issue. Whether you’re a seasoned DIYer or just curious about what’s happening under the hood, this guide will help you stay ahead of the problem.
Let’s dive in and uncover the telltale signs of a crank sensor on its last legs.

Table of Contents
What Does the Crank Sensor Do?
Top Signs of a Bad Crank Sensor
What Does the Crank Sensor Do?
The crankshaft position sensor is like the brain’s messenger for your engine. It constantly monitors the position and speed of the crankshaft—the rotating shaft that converts the energy from your pistons into usable power for your wheels.
This sensor sends real-time data to your car’s engine control module (ECM), telling it exactly when to fire the spark plugs and inject fuel into the cylinders. Without this precise timing, your engine wouldn’t run efficiently—or at all.
Think of the crank sensor as the conductor in an orchestra. If it’s off, your engine’s entire performance goes out of sync. Misfires, rough idling, or even a dead engine are just some of the issues you’ll face when this critical sensor starts to fail.
In short, the crank sensor is a small component with a big job: ensuring your engine fires at the right time, every time. You probably won’t even think about it when it’s working properly. But it can throw your entire engine into chaos when it goes bad.
Why the Crank Sensor Fails
Crankshaft position sensors may be small, but they work hard under harsh conditions, and over time, this can take a toll. Several factors can cause a crank sensor to fail, and understanding them can help you spot issues early or even prevent failure altogether.
- Heat Damage
The crank sensor sits close to the engine, where temperatures can soar. Over time, constant exposure to extreme heat can cause the sensor’s internal components to degrade, leading to failure. - Electrical Problems
Wiring issues, corroded connections, or damaged sensor circuits can disrupt the flow of information from the crank sensor to the ECM. A frayed wire or loose connection might cause intermittent issues. - Oil and Dirt Contamination
Leaking engine oil or dirt buildup can coat the sensor, making it less effective at reading the crankshaft’s position. - Physical Damage
Vibrations from the engine, accidental impacts during repairs, or a failing Aux or timing belt can cause direct damage to the sensor or its mounting point, making it inoperable. - Ageing and Wear
Like most components, the crank sensor has a limited lifespan. After years of service, internal wear can cause it to fail.
A failing crank sensor doesn’t always quit suddenly; it often gives warning signs like rough idling, trouble starting the engine, or causing the engine to shut down, but only when the engine reaches operating temperature. Understanding these causes can help you act quickly, saving you from getting stranded or facing a costly repair later on.
Top Signs of a Bad Crank Sensor
When the crankshaft position sensor starts to fail, it doesn’t go quietly. It’s one of those components that gives you plenty of warning—if you know what to look for. Below are the most common symptoms to watch for, and if you notice one (or more), it’s time to investigate.
Engine Stalling or Cutting Out
A bad crank sensor can disrupt the signal to your car’s engine control module (ECM), causing the engine to stall unexpectedly. This might happen while idling, cruising, or accelerating, leaving you in a nerve-wracking situation.
Some failing sensors only malfunction after the engine heats up. This is due to a phenomenon called “heat soak,” where the heat from the engine causes the internal components of the sensor to break down and fail.
Difficulties Starting the Engine
If your car takes forever to start or won’t start at all, a faulty crank sensor could be to blame. Without accurate data on the crankshaft’s position, the ECM doesn’t know when to fire the spark plugs, and the engine just won’t crank over properly.
Engine Misfires
When the crank sensor isn’t sending precise signals, your engine’s timing gets thrown off. The result? Misfires make the engine run rough, hesitate during acceleration, or shake at idle.
Check Engine Light Illuminated
One of the first clues you’ll get is often a glowing check engine light on your dashboard. Modern vehicles are good at detecting crank sensor issues, and the ECM will usually log a diagnostic trouble code (DTC) to point you in the right direction. The most common crank sensor fault code is P0335.
Reduced Engine Performance
A failing crank sensor can mess with the timing and fuel injection, leaving your engine sluggish, underpowered, or even unable to maintain a steady speed. You might notice poor throttle response or feel like your car is struggling to perform.
These symptoms can be frustrating and often show up intermittently, making the issue hard to pinpoint. If you’re experiencing any of these problems, it’s time to dig deeper or consult a scan tool for trouble codes. Ignoring the signs could leave you stranded at the worst possible time.
How to Test a Crank Sensor
Testing a crankshaft position sensor might sound complicated, but it’s manageable for most DIYers with the right tools and a step-by-step approach. Here’s how you can determine if the crank sensor is the culprit behind your engine troubles.
What You’ll Need:
- A multimeter (preferably digital)
- A scan tool (optional, but useful for pulling trouble codes)
- Basic hand tools (to access the sensor)
Step 1: Locate the Crank Sensor
Start by finding the crankshaft position sensor. Depending on your car, it’s typically mounted near the crankshaft pulley, flywheel, or bell housing. Check your repair manual or an online guide for the exact location.
Step 2: Check for Trouble Codes
Before diving in, connect a scan tool to your car’s OBD-II port and look for trouble codes. Codes like P0335 indicate a crank sensor issue. While this doesn’t confirm the sensor is faulty, it’s a good starting point. Common crank fault codes and their description include:
P0335: Crankshaft Position Sensor “A” Circuit Malfunction
This is the most common code associated with crank sensor failure. It indicates the ECM is not receiving a proper signal from the sensor.
Potential Causes:
- Faulty crank sensor
- Damaged or corroded wiring
- Loose or broken connector
P0336: Crankshaft Position Sensor “A” Circuit Range/Performance
This code means the sensor is sending erratic or out-of-range signals.
Potential Causes:
- Failing sensor
- Interference from other electrical components
- Damaged reluctor wheel (the toothed wheel fixed to the crankshaft that the sensor reads)
P0337: Crankshaft Position Sensor “A” Circuit Low Input
This code occurs when the ECM detects an unusually low signal from the sensor.
Potential Causes:
- Faulty sensor
- Poor electrical connection
- Sensor wiring shorted to ground
P0338: Crankshaft Position Sensor “A” Circuit High Input
This indicates the sensor signal is abnormally high or exceeding expected parameters.
Potential Causes:
- Sensor failure
- Open circuit in the wiring
- Signal interference
P0339: Crankshaft Position Sensor “A” Circuit Intermittent
This code appears when the ECM detects an intermittent signal loss from the crank sensor.
Potential Causes:
- Loose connector or damaged wiring
- Sensor beginning to fail
- Vibrations or movement causing signal loss (possibly loose sensor fasteners)
Other Related Codes:
- P0016: Crankshaft-Camshaft Position Correlation (Bank 1 Sensor A)
Indicates a timing issue between the crankshaft and camshaft, which could be caused by a faulty crank sensor or a stretched timing belt/chain.
If your OBD-II scanner shows one of these codes, it indicates that the crank sensor or its related wiring needs attention. Testing the sensor and inspecting its connections can confirm the diagnosis before replacement.
Step 3: Perform a Visual Inspection
Inspect the sensor and its wiring for obvious signs of damage, such as damaged wires, oil contamination, or loose connections. Sometimes, the issue isn’t the sensor itself but a wiring fault. Rodents especially love to eat underhood wiring insulation, so keep a sharp eye for evidence of the presence of rodents.
Don’t forget to check the relocator wheel (if accessible) loose, missing or impact damage to teeth will cause erratic crank signals and set a code.
Step 4: Test the Sensor with a Multimeter
Most crank sensors are two-wire units that generate a voltage when the crankshaft fixed reluctor wheel passes by. To test the sensor, we’ll check for voltage while cranking the engine. However, it’s important to note that this is a basic test and only effective for identifying sensors that have completely failed. It won’t detect intermittent issues or sensors producing outputs below the required specifications.
A better way to test is with a scan tool with live data feature (covered below).
- Unplug the Sensor: Disconnect the wiring harness from the crank sensor.
- Set Your Multimeter: Switch your multimeter to volts.
- Check for Signal Output (Voltage): Crank the engine and measure the sensor’s signal. A fluctuating reading indicates the sensor is working. No signal? It’s likely faulty.
Using a scan tool
Using a scan tool with live data capabilities is the preferred method; it provides more insight into how the crank sensor is functioning while the engine is running/cranking.
- Connect the Scan Tool: Plug the scan tool into your car’s OBD-II port and access the live data feature (some also have graph features; if so, choose it)
- Monitor RPM Data: Start the engine and look for the crank sensor’s output, typically displayed as engine RPM.
- If the sensor is working properly, the RPM reading will respond smoothly as the engine accelerates or decelerates.
- If the reading jumps erratically, cuts out, or doesn’t register at all, the sensor or its wiring could be faulty.
- Compare to Factory Specs: Some scan tools can display more detailed data about the crank sensor. Compare this information to the manufacturer’s specifications to identify irregularities.
Advanced Testing with an Oscilloscope
A technician might use an oscilloscope to test the crank sensor’s signal in a professional shop. This tool can display the sensor’s waveform, which visually represents its output signal.
- What to Look For: A healthy crank sensor produces a consistent and clean waveform. Irregularities, such as missing signals or spikes, can indicate internal damage or issues with the reluctor wheel.
- Why It’s Useful: Unlike a multimeter or scan tool, an oscilloscope can detect subtle issues that may not trigger a diagnostic trouble code but still affect performance.
While using a scope requires specialized equipment and expertise, the live data method with a scan tool is a practical option for most DIYers. Together, these tests can confirm whether your crank sensor is the root of your engine problems or if further diagnosis is needed.
Step 5: Wiggle Test
Reconnect the sensor and start the engine. Wiggle the sensor’s wiring while the engine runs. If it stumbles or stalls, you’ve got a wiring issue.
Step 6: Replace If Necessary
If the sensor fails the resistance or signal test, it’s time for a replacement. Most crank sensors are affordable and relatively easy to swap out.
Replacing a Crank Sensor
Replacing a crankshaft position sensor is usually a straightforward job, but its location can make it tricky on some vehicles. Crank sensors are commonly found near the harmonic balancer at the front of the engine or at the bell housing pointing toward the crankshaft. Let’s walk through the process step by step, covering both scenarios.
Tools You’ll Need:
- Socket set and ratchet
- Wrenches (as needed)
- Screwdrivers
- Penetrating oil
- Harmonic balancer puller (if required)
- Torque wrench (recommended for reassembly)
- Good hand light
Step 1: Locate the Sensor
Refer to your repair manual or online guide to find the exact location of your crank sensor.
- Harmonic Balancer Location: This sensor is mounted at the front of the engine, close to the crankshaft pulley.
- Bell Housing Location: This sensor is installed at the back of the engine, near where the transmission meets the engine block.
Step 2: Prepare for the Job
- Use a jack and jack stands to lift the car if the sensor is hard to access.
- Take pictures during disassembly to ensure everything goes back together correctly.
- Apply penetrating oil to relevant fasteners and allow to soak before starting the job.
Step 3: Remove the Old Sensor
For Sensors at the Harmonic Balancer
- Easy-to-Access Sensors: Remove the mounting bolt(s) and unplug the sensor from the wiring harness. Gently wiggle and pull the sensor out.
- Behind the Harmonic Balancer:
- Remove the auxiliary belt.
- Use a harmonic balancer puller to remove the crankshaft pulley.
- Once exposed, remove the sensor’s bolts and wiring connection. Pull out the sensor.
For Sensors at the Bell Housing
- Easily Accessible Sensors: Remove the mounting bolt(s) and wiring connector, then pull the sensor straight out.
- Hard-to-Access Sensors:
- If the sensor is tucked away or blocked, you may need to remove surrounding components for better access.
- In extreme cases, the transmission may need to be removed to reach the sensor. This is a much bigger job and often better left to a professional unless you have the right tools and experience.
Step 4: Install the New Sensor
- Inspect the Mounting Area: Check for debris, oil, or dirt in the sensor’s hole and clean it if necessary.
- Install the New Sensor: Carefully position the new sensor into place, ensuring it sits flush.
- Secure the Sensor: Reinstall and tighten the mounting bolt(s). A torque wrench is not necessary for these bolts.
- Reconnect the Wiring: Attach the sensor’s electrical connector securely.
Step 5: Reassemble the Surrounding Components
- For harmonic balancer sensors, reinstall the pulley and torque to spec. Refit the auxiliary belt and ensure its ribs are seated correctly in all the pulleys before starting the engine.
- For bell housing sensors, reassemble any components removed for access.
Step 6: Test the Repair
- Start the engine and check for smooth operation. If the sensor was the issue, symptoms like hard starting, stalling, or a check engine light should be resolved.
- Use a scan tool to clear any stored trouble codes and verify the fix.
Replacing a crank sensor can range from a quick afternoon fix to a more involved job. Knowing what’s involved ahead of time will save you from surprises, and as always, patience and preparation are your best tools.
Crank Sensor FAQs
Here are some of the most frequently asked questions about crankshaft position sensors, with straightforward answers to help you understand this critical part of your engine.
Q: Can you drive with a bad crank sensor
A: It’s not recommended. A failing crank sensor can cause your engine to stall, hesitate, or even fail to start, leaving you stranded. Driving with a faulty sensor can also lead to further engine damage in some cases.
Q: How do you test a crank sensor
A: Testing involves using a multimeter to check the sensor signal output. A scan tool can also help by identifying trouble codes related to the crank sensor, such as P0335.
Q: How much does it cost to replace a crank sensor?
A: The cost varies depending on the vehicle and sensor location. Most sensors cost between $50 and $150, with labor costs ranging from $100 to $300. Hard-to-reach sensors (e.g., those requiring transmission removal) will cost more due to additional labour.
Q: Will a bad crank sensor trigger a check engine light?
A: Yes, in most cases. The ECM monitors the crank sensor, and when it detects an issue, it will store a diagnostic trouble code (DTC) and illuminate the check engine light.
Q: Can a bad crank sensor damage my engine?
A: Indirectly, yes. If the sensor fails completely, the engine may stall or refuse to start. Prolonged driving with a faulty sensor can also stress other components, such as the ignition system or catalytic converter.
If you suspect a crank sensor issue, addressing it quickly can save you time, money, and frustration. It’s one of those parts you don’t think about—until it stops working!
You may find the following pages useful:
- About the Author
- Latest Posts
John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.