Quick answer
A faulty crankshaft position sensor usually causes a check engine light, hard starting or no start, stalling when the engine is hot, misfires, rough idle and worse fuel economy. Common codes are P0335–P0339. Replacement typically costs $120–$400, and the part alone is often $20–$150.
- What it does
- Tells the engine control unit the crankshaft's position and rotational speed, so it can control ignition timing and fuel injection.
- Top symptoms
- Check engine light, cranks but won't start, stalling when warm, misfires, rough idle, poor fuel economy.
- Common codes
-
P0335P0336P0337P0338P0339 - Typical cost
- $120–$400 total; more if the sensor sits behind the flywheel or transmission.
- Safe to drive?
- Not for long. A bad crankshaft sensor can stall the engine suddenly in traffic.
Check it on the go: plug in the Carista OBD2 adapter and read fault codes and live engine RPM data from your phone.
What does a crankshaft position sensor do?
The crankshaft position sensor (CKP sensor) tracks the exact position and rotational speed of the crankshaft and sends that signal to the engine control unit (ECU). The ECU is the brain of your engine management system. Without a clean CKP signal, it cannot work out when to fire the spark plugs or open the fuel injectors.
Most modern crankshaft sensors are either magnetic (inductive) or Hall-effect types. They read a toothed reluctor wheel on the crankshaft or flywheel. A missing tooth or gap in the wheel gives the ECU a reference point for top dead center.
The ECU uses the CKP signal for three key engine control jobs:
- Ignition timing: firing each spark plug at the right moment in the combustion cycle.
- Fuel injection: timing and sizing each injector pulse, together with the camshaft position sensor.
- Engine speed (RPM): the rotational speed reading shown on your tachometer and used by the transmission and stability systems.
The sensor usually sits near the crankshaft pulley at the front of the engine, on the side of the engine block, or near the flywheel by the transmission bellhousing. Its location has a big effect on replacement cost.
8 symptoms of a faulty crankshaft position sensor
The symptoms of a faulty crankshaft sensor often come and go at first, then get worse as the sensor or its wiring degrades. Here are the signs to watch for.
1. Check engine light comes on
The check engine light is usually the first warning. When the ECU sees a missing, weak or erratic CKP signal, it stores a diagnostic trouble code (DTC) and lights the warning lamp.
The light can also appear with misfire codes (P0300–P0308) or a crank/cam correlation code (P0016–P0019).
2. Engine cranks but won't start
If the CKP signal drops out completely, many engines will crank but never fire. The ECU has no reference for spark or fuel injection, so it shuts both off as a safety measure.
3. Engine stalls, especially when hot
A failing sensor often works when cold and cuts out once the engine bay heats up. Heat expands internal cracks in the sensor or its wiring. The engine may stall at idle or while driving, then restart after it cools down.
4. Misfires and engine stumbling
A weak or noisy signal throws off ignition timing. You may feel jerking, stumbling or hesitation under load, and the ECU may log random misfire codes.
5. Rough idle and vibration
An unstable RPM signal makes the idle surge or shake. You may notice the tachometer needle jumping or dropping to zero while the engine is still running.
6. Poor acceleration and power loss
When ignition timing and fuel injection drift, the engine loses power. Some cars enter limp mode to protect the engine, limiting RPM and speed.
7. Worse fuel economy
Mistimed injection wastes fuel. A drop in fuel economy, together with any of the signs above, points to a sensor problem rather than driving habits.
8. Erratic tachometer or shifting issues
On many cars the tachometer and automatic transmission rely on the same rotational speed data. A bad crankshaft sensor can cause a jumpy rev counter, harsh shifts or a dead tachometer.
What causes a bad crankshaft position sensor?
Most crankshaft sensor failures come from heat, contamination or wiring damage, not from the sensor simply wearing out. The usual causes are:
- Heat cycling: years of heating and cooling crack the sensor's internal windings or electronics.
- Damaged or corroded wiring: chafed harnesses, broken wires and green, corroded connector pins interrupt the signal.
- Oil or coolant leaks: a leaking valve cover, rear main seal or water pump can soak the sensor and degrade its seal.
- Metal debris: magnetic sensors attract fine metal particles that blur the signal.
- Incorrect air gap: a sensor that sits too far from the reluctor wheel after a repair gives a weak reading.
- Damaged reluctor wheel: bent, cracked or missing teeth on the tone ring mimic a sensor fault.
- Electrical problems: a weak battery, poor grounds or a failing alternator can create a noisy signal.
Because wiring and reluctor-wheel faults set the same codes, check the connector and harness before you buy a new sensor.
How to diagnose a faulty crankshaft position sensor
Start with the fault codes. They tell you whether the ECU has flagged the crankshaft sensor circuit or something else, such as the camshaft sensor or fuel system.
- Scan for codes. Connect Carista OBD2 scanner to the port under the dashboard and read the stored and pending codes. Look for P0335–P0339 and any misfire or crank/cam correlation codes.
- Check live data. With the engine cranking or idling, watch the engine RPM reading. A reading of 0 RPM while cranking, or an RPM value that drops out at random, points to a missing CKP signal.
- Inspect the wiring and connector. Look for oil soaking, chafed insulation, loose plugs and corroded pins.
- Test the sensor. A mechanic can check resistance on magnetic sensors or the signal pattern with an oscilloscope. Compare results with the manufacturer's specification.
- Clear the codes and re-test. After a repair, clear the codes and drive the car. If the check engine light stays off, the fix worked.
Read more: How to Read OBD2 Live Data: A Step-by-Step Guide
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Crankshaft position sensor replacement cost
Most drivers pay about $120–$400 to replace a crankshaft position sensor at a shop. The sensor itself is cheap; labor and access drive the final bill. For example, RepairPal estimates $169–$226 for a 2025 Chevrolet Tahoe and $161–$306 for a 2016–2017 Honda HR-V.
What moves the price:
- Sensor location: front-mounted sensors take minutes; some engines require removing the starter, intake or even the transmission.
- Part quality: OEM or OE-supplier sensors cost more but are less likely to fail early.
- Labor rates: dealers charge more per hour than independent shops.
- Extra repairs: a damaged harness, connector or reluctor wheel adds to the bill.
DIY replacement is realistic on many cars with an accessible sensor. Disconnect the battery, unplug and unbolt the old sensor, fit the new one with the correct air gap, then clear the codes with Carista OBD2 scanner. Some vehicles also need a crankshaft position relearn procedure after replacement.
Can you drive with a bad crankshaft position sensor?
You can sometimes drive short distances, but it isn't safe to keep doing it. A failing sensor can cut the engine without warning, which means sudden loss of power steering assist and brake boost in traffic. It can also leave you stranded with a car that cranks but won't start.
To keep crankshaft sensors healthy and catch problems early:
- Fix oil and coolant leaks near the sensor promptly.
- Keep the battery, alternator and ground connections in good condition.
- Use a quality replacement sensor and set the correct air gap.
- Scan for codes as soon as the check engine light appears, before an intermittent fault becomes a no-start.
FAQs
How do I know if my crankshaft position sensor is bad?
Look for a check engine light with codes P0335–P0339, cranking without starting, stalling when hot, misfires and a jumpy tachometer. Confirm it by reading the codes and watching live RPM data with an OBD2 scanner such as Carista.
What happens when a crankshaft position sensor fails while driving?
The engine can stall suddenly because the ECU loses its ignition timing and fuel injection reference. It may restart after cooling down, but the fault will return.
How much does it cost to replace a crankshaft position sensor?
Typically $120–$400 including parts and labor. It can exceed $600 if the sensor sits behind the flywheel or transmission.
Can I replace a crankshaft position sensor myself?
Often, yes. Accessible sensors take 30–60 minutes with basic tools. Clear the codes afterwards, and check whether your car needs a crankshaft relearn procedure.
Can a bad crankshaft sensor damage the engine?
It rarely causes direct mechanical damage. However, misfires can overheat the catalytic converter, and sudden stalling is a safety risk.
Can I check a crankshaft position sensor with my phone?
Yes. Plug a Bluetooth Scanner like the Carista OBD2 tool into the OBD2 port, then use the Carista app to read fault codes and view live engine data.
*Disclaimer: The information provided in this article is intended for educational and informational purposes only and should not be considered as professional advice. While we strive to provide accurate and up-to-date content regarding OBD2 tools, diagnostics, and related automotive issues, the specifics of each vehicle may vary.
*Always consult your vehicle’s manufacturer guidelines and consider seeking professional assistance when dealing with complex or critical diagnostic issues.
