Crankshaft Position Sensor vs Camshaft Sensor Failure Symptoms Comparison

When your car starts acting up stalling at red lights, misfiring under acceleration, or refusing to start on a cold morning two small sensors sit near the top of the suspect list: the crankshaft position sensor and the camshaft position sensor. They share overlapping symptoms, which makes figuring out which one failed a real headache for DIYers and even some mechanics. Knowing how their failure symptoms differ can save you hours of diagnostic time and prevent you from replacing the wrong part.

What Does the Crankshaft Position Sensor Do?

The crankshaft position sensor (CKP) monitors the speed and position of the crankshaft as it rotates. The engine control module (ECM) uses this signal to determine exactly when to fire the spark plugs and inject fuel. Without a clean CKP signal, the ECM essentially loses its timing reference and the engine either runs poorly or won't start at all.

Most CKP sensors sit near the crankshaft pulley or the flywheel/flexplate. They read a reluctor ring (a toothed wheel) and generate a signal the ECM interprets as RPM and crank angle.

What Does the Camshaft Position Sensor Do?

The camshaft position sensor (CMP) tracks the position of the camshaft(s). The ECM uses this data to figure out which cylinder is on its compression stroke so it can sequence the fuel injection and ignition events correctly. It also helps the ECM detect valve timing problems.

On most engines, the CMP sensor mounts near the cylinder head, reading a reluctor on the camshaft gear or sprocket. On engines with variable valve timing (VVT), the CMP signal helps the ECM control cam phasing for performance and emissions.

Crankshaft Position Sensor Failure Symptoms

CKP sensor problems tend to cause more dramatic and immediate drivability issues because the sensor feeds the primary timing signal. Common symptoms include:

Engine cranks but won't start The ECM has no RPM reference, so it won't command spark or fuel.
Random stalling The engine dies without warning, often at low speed or idle. This is a hallmark symptom, especially when the sensor fails intermittently and sets no trouble codes.
No start when hot A failing CKP sensor can work fine when cold but lose its signal once it heats up. Heat soak failures are common on certain GM, Chrysler, and Ford applications, as described in this breakdown of heat-related CKP failures.
Rough idle or misfiring An erratic CKP signal causes spark timing to fluctuate.
RPM gauge drops to zero while driving On many vehicles, the tachometer reads directly from the CKP signal. If it cuts out, the gauge drops.
Check engine light with codes like P0335, P0336, P0337, or P0338 Though notably, some CKP failures produce stalling with no stored codes at all.

A CKP failure that kills the engine without setting a code is one of the trickiest situations. The vehicle may die while driving with no check engine light, leaving you to diagnose based on symptoms alone.

Camshaft Position Sensor Failure Symptoms

CMP sensor failures are generally less severe because many engine management systems can fall back on the CKP signal alone. The ECM uses a default timing strategy and the engine usually still runs. Common symptoms include:

Hard starting or longer cranking time The engine eventually starts, but the ECM takes extra time to sync timing without the CMP reference.
Reduced engine performance Acceleration feels sluggish because the ECM can't optimize fuel injection sequencing or VVT phasing.
Lower fuel economy The default timing strategy runs richer and less efficiently.
Check engine light with codes like P0340, P0341, P0342, P0343, P0344, P0345, P0349, P0365, or P0369.
Engine stalling at idle Less common than with CKP failure, but possible, especially on engines that rely heavily on the CMP for idle control.
VVT-related rough running On engines with cam phasing, a bad CMP can cause the VVT system to malfunction, leading to rough idle, hesitation, or a rattling noise at startup.

How Do You Tell the Difference Between the Two?

This is where most people get stuck. Here are practical ways to narrow it down:

Does the engine start at all?

If the engine cranks strong but absolutely will not fire, suspect the CKP sensor first. A CMP failure almost always still allows the engine to start, even if it takes longer or runs rough afterward.

Are there diagnostic trouble codes?

CKP-specific codes (P0335–P0341 range, depending on manufacturer) point to the crankshaft sensor. CMP codes (P0340, P0344, P0365, etc.) point to the camshaft sensor. But be aware: on some vehicles, a failing CKP can actually trigger CMP codes because the ECM cross-references both signals. Always test before replacing parts.

Does the tachometer work during cranking?

On vehicles where the tach reads from the CKP, a dead gauge during cranking suggests a CKP problem. If the tach shows RPM while cranking but the engine won't start, the CKP is likely sending a signal and the problem lies elsewhere.

How does the engine stall?

A CKP failure tends to cause sudden, complete engine shutdown no sputtering, just an instant loss of power. A CMP-related stall is more likely to involve rough running, stumbling, and a gradual loss of power before the engine dies.

Common Mistakes When Diagnosing These Sensors

Replacing the camshaft sensor when the crankshaft sensor is the real problem. This is the single most common misdiagnosis. Because CMP codes can appear when the CKP is actually failing, people swap the cam sensor and waste money.
Not checking wiring and connectors first. A corroded connector or chafed wire can mimic a sensor failure. Inspect the harness before replacing the sensor.
Ignoring intermittent failures. A CKP or CMP that only acts up when hot might test fine on the bench. If you can't catch the failure with a scan tool, try heating the sensor with a heat gun and monitoring the signal with an oscilloscope or multimeter.
Assuming the sensor is always the problem. A damaged reluctor ring, excessive crankshaft end play, a stretched timing chain, or a worn tone ring can all produce similar symptoms. The sensor itself may be fine.
Clearing codes before driving the vehicle. Freeze-frame data tells you the operating conditions when the fault occurred. Clear it and you lose valuable clues.

Can Both Sensors Fail at the Same Time?

It's uncommon but not impossible. A shared wiring issue like a damaged ground circuit or a corroded splice in the engine harness can take out both sensor signals simultaneously. If both CKP and CMP codes appear together, check the shared power and ground circuits before replacing either sensor.

How Much Does It Cost to Replace Each Sensor?

CKP and CMP sensors are generally inexpensive parts. Expect $15–$75 for the sensor itself on most vehicles, with some European makes running higher. Labor varies depending on accessibility:

Crankshaft position sensor: $50–$250 labor. Some are easy to reach from underneath; others require removing the starter motor or other components.
Camshaft position sensor: $40–$180 labor. These usually sit on top of or near the cylinder head, making them more accessible.

Both sensors are reasonable DIY jobs on most vehicles if you have basic tools and the sensor is accessible. Always use OEM or high-quality aftermarket sensors cheap sensors from unknown brands have a much higher failure rate and can create false signals that confuse the ECM.

Real-World Example

A 2012 Chevrolet Equinox with the 2.4L Ecotec engine starts stalling randomly at traffic lights. No check engine light. The owner replaces the camshaft position sensor based on a forum suggestion. The stalling continues. A mechanic later checks with an oscilloscope and finds the crankshaft position sensor signal dropping out intermittently when the sensor reaches operating temperature. Replacing the CKP sensor fixes the problem. This scenario plays out daily in shops across the country.

Quick Diagnostic Checklist

□ Note exactly when the problem occurs at startup, when hot, at idle, under load, or randomly
□ Scan for codes and record freeze-frame data before clearing anything
□ Check for both CKP and CMP codes, not just one
□ Visually inspect both sensor connectors and wiring for damage, corrosion, or oil contamination
□ Check the CKP sensor's air gap and reluctor ring condition if accessible
□ Monitor the CKP signal with a scan tool or oscilloscope during cranking and running
□ Monitor the CMP signal the same way
□ If the engine won't start, check for RPM signal on the scan tool during cranking no RPM usually means CKP failure
□ Test the sensor's resistance with a multimeter per the manufacturer's specifications
□ Consider heat-testing the sensor if the failure is temperature-dependent

Next step: If you're dealing with a no-start or random stalling condition, start by scanning for codes and checking the CKP signal during cranking. The crankshaft sensor is the more common failure and the one that causes the most noticeable symptoms. If that checks out clean, move to the camshaft sensor and its wiring. And if your car is stalling with no codes at all, that's a strong hint pointing toward an intermittent crankshaft position sensor failure one of the most overlooked diagnostic scenarios on modern engines.

Reference: For general information on OBD-II diagnostic trouble codes, see the OBD-Codes.com trouble code database.