The crankshaft position sensor (CKP) provides the engine control module with a primary reference for crankshaft angle and engine speed. The camshaft position sensor (CMP) provides a camshaft phase reference that helps the module identify where the engine is in its combustion cycle and which cylinder is ready for a particular event.
The module uses these signals together to coordinate functions such as ignition and fuel injection and to monitor camshaft timing on applicable engines. Exactly how it uses each signal, whether the engine can start without one of them, and which fallback strategies are available depend on the vehicle.
If you are comparing a crankshaft sensor vs camshaft sensor because a car is hard to start, stalls, or stores a position sensor code, that distinction matters. A symptom or trouble code can point you toward a circuit, but it cannot prove that the sensor itself has failed. Wiring, power supply, a trigger wheel, mechanical timing, and variable valve timing (VVT) faults can affect the same signals.
Crankshaft vs Camshaft Position Sensor at a Glance
| Feature | Crankshaft position sensor (CKP) | Camshaft position sensor (CMP) |
|---|---|---|
| What it detects | Crankshaft rotation and position | Camshaft rotation and position |
| Main information supplied | A crankshaft angle and engine speed reference | A camshaft phase reference and information used for cylinder identification |
| Typical target | A reluctor or trigger wheel associated with the crankshaft | A trigger wheel, target, or feature associated with a camshaft |
| Usual location | Near the crankshaft pulley, engine block, flywheel, or transmission bellhousing, depending on the engine | Near a cylinder head, timing cover, camshaft gear, or distributor assembly, depending on the engine |
| Common related code families | P0335–P0339 for CKP circuit faults | P0340–P0349 for CMP circuit faults |
| Useful scan data | Engine RPM during cranking | CMP or cam/crank synchronization status, where supported |
| If its signal is lost | The engine may stall or crank without starting; the outcome depends on the control strategy | The engine may crank longer, run using a fallback strategy, or fail to start; the outcome depends on the control strategy |
The practical distinction in a crankshaft vs camshaft position sensor comparison: CKP is the primary crankshaft position and speed reference; CMP adds camshaft phase information. The control module interprets both signals according to the engine’s design and operating conditions.
What Does a Crankshaft Position Sensor Do?
The crankshaft position sensor location varies by engine; the sensor detects a rotating target associated with the crankshaft. As the target passes the sensor, it generates a signal that the engine control module uses to calculate crankshaft position and engine speed.
That information is central to engine operation. Depending on the vehicle, the module uses it to schedule ignition and fuel injection, recognize engine rotation during starting, and monitor changes in crankshaft speed associated with misfires.
A CKP sensor does not usually inspect a piston directly. The control module infers crankshaft position from the sensor signal and the known shape of the trigger target. A reference feature, such as a missing-tooth gap on some engines, helps the module establish a repeatable position.
If the module loses the CKP signal, it may no longer have the information needed to calculate engine speed or schedule combustion events. This is why a CKP signal problem can cause a stall or a crank-but-no-start condition. The exact response varies by vehicle.
What Does a Camshaft Position Sensor Do?
The camshaft position sensor location varies by engine; the sensor detects a target associated with a camshaft. Its signal tells the control module the camshaft’s position relative to the crankshaft.
On a four-stroke engine, the crankshaft turns twice for each one camshaft revolution. Crankshaft position alone may not tell the module which of two possible strokes a cylinder is on. The CMP signal helps identify the engine’s position in the full 720-degree combustion cycle.
Depending on the engine design, CMP information supports cylinder identification, sequential fuel injection, starting strategy, and VVT monitoring. An engine may have one CMP sensor or several, including separate sensors for intake and exhaust camshafts.
The sensor reports camshaft position; it does not open the valves or adjust valve timing by itself. If a camshaft is mechanically out of time, a working CMP sensor can still report a position the control module considers incorrect.
How Do Camshaft and Crankshaft Position Sensor Signals Work Together?
The control module compares the CKP and CMP patterns to establish engine position and cylinder identification. That comparison is often called cam/crank synchronization.
The camshaft and crankshaft position sensor signals also help the module check whether camshaft position is plausible relative to crankshaft position. On a VVT engine, the expected relationship may change as the camshaft is commanded to advance or retard.
This is where a common misunderstanding causes unnecessary sensor replacements: a cam/crank correlation fault does not necessarily mean either sensor is defective. Both sensors can generate clear signals while a stretched timing chain, incorrectly installed belt, moved trigger wheel, or VVT problem changes the timing relationship between them.
An oscilloscope can display both signals at once. A technician can compare a chosen CMP edge with a CKP reference feature under the vehicle manufacturer’s specified conditions, then check the result against service data or a known-good capture from the same engine. Pico Technology demonstrates this comparison in its cam and crank correlation guide.
Camshaft and Crankshaft Sensor Symptoms: Can You Tell Which Is Bad?
Usually, no. CKP and CMP faults can both be associated with a check engine light, extended cranking, intermittent starting, stalling, hesitation, rough running, or misfires. Fuel, ignition, wiring, and mechanical faults can cause many of the same complaints.
Comparing camshaft and crankshaft sensor symptoms can guide the first checks, but the pattern cannot confirm a failed sensor:
| What you observe | What to investigate |
|---|---|
| The engine cranks but scan data shows 0 RPM | CKP signal, CKP wiring, power or ground where applicable, starting speed, and scan-data availability |
| Cranking RPM is present but cam/crank sync is absent | CMP signal, CMP circuit, CKP pattern, trigger targets, and mechanical timing |
| The fault appears after the engine warms up | A signal or wiring fault that changes with heat, among other possible causes |
| The engine stalls and the RPM signal disappears at the same time | CKP circuit and related wiring are important checks |
| Rough running occurs with cam timing or VVT codes | Check commanded versus actual cam position, oil-related VVT operation, and mechanical timing |
Cranking RPM is a clue about the crankshaft signal, not a CMP test. A normal RPM reading does not prove the CMP signal is present. Likewise, a zero RPM reading does not prove the CKP sensor itself is bad; the cause still needs to be isolated.
Some engines can start or continue running when a CMP signal is lost by using a fallback strategy. Others may take longer to start or may not start. Do not use “it still starts” as a universal rule for ruling out CMP faults.
CKP vs CMP Trouble Codes: What Do They Tell You?
A camshaft vs crankshaft code comparison can help prioritize checks. A trouble code describes what the control module detected in a circuit or system. It is the beginning of diagnosis, not a replacement instruction.
| Code or code family | General diagnostic direction |
|---|---|
| P0335–P0339 | CKP circuit, signal performance, high or low input, or intermittent signal |
| P0340–P0344 | CMP circuit and signal faults generally associated with Bank 1 or a single-bank engine |
| P0345–P0349 | CMP circuit and signal faults generally associated with Bank 2 on applicable engines |
| P0016–P0019 | Camshaft-to-crankshaft position correlation; check the specified bank and camshaft, including timing and VVT causes |
These code numbers provide a general direction. The exact definition, diagnostic criteria, bank, and sensor position must be confirmed in the OEM service information for that vehicle. Bank 2 applies only where the engine has a second bank, and labels such as Sensor A or Sensor B should not be assigned to an intake or exhaust camshaft without checking the vehicle-specific definition. Manufacturers may also provide additional codes or descriptions.
If CKP and CMP codes appear together, do not assume both sensors failed at the same time. Check freeze-frame data and the order in which faults occurred, then investigate shared power or ground circuits, wiring, trigger targets, and loss of synchronization. A correlation code can also appear when both sensors work but their signals no longer have the expected timing relationship.
Crankshaft Sensor vs Camshaft Sensor: How to Check Which Needs Attention
A useful crankshaft sensor vs camshaft sensor diagnosis moves from information the vehicle already provides to direct circuit and signal tests.
1. Scan the vehicle before clearing codes
Record all stored and pending codes, their full descriptions, and available freeze-frame data. Check whether the complaint occurs during cranking, at idle, when hot, or while driving.
If the vehicle supports enhanced engine data, look for Engine RPM, CMP signal or cylinder identification status, Cam/Crank Sync, and desired versus actual camshaft angles. The names and availability of these parameters vary by vehicle and scan tool.
2. Check Engine RPM while cranking
If the starter is rotating the engine and scan data consistently shows 0 RPM, investigate why the control module is not reporting engine speed. The CKP circuit is a key possibility, but a weak battery, slow cranking, control-module power problem, or scan-data limitation can also affect the result.
If RPM is present, the module is receiving enough information to calculate speed. That does not establish that every CKP pulse is correct or that the CMP signal is valid.
3. Check cam/crank synchronization, if available
A sync status that fails to change to “Yes” can indicate a missing or implausible signal or an incorrect relationship between the signals. It does not identify which component caused the problem.
If the scan tool displays desired and actual camshaft angles, compare them under the engine speed, load, oil temperature, and other conditions specified by the manufacturer. A persistent difference may direct attention toward VVT control, oil supply, a cam phaser, or mechanical timing.
4. Inspect the sensor circuits and targets
Confirm the correct sensor and connector from the wiring diagram. Inspect for damaged wiring, loose or corroded terminals, contamination inside connectors, incorrect sensor installation, and visible trigger-target damage.
Wire count is only an initial clue. A three-wire sensor may use an active design, while a two-wire sensor may be passive or active. Use the wiring diagram, sensor identification, and manufacturer’s test method to determine whether the circuit uses a variable-reluctance, Hall-effect, magnetoresistive, or other design. Confirm its pinout, supply, ground, expected signal, and installation requirements before testing.
5. Compare the actual signals when needed
A multimeter can help check power, ground, and basic signal activity. An oscilloscope is more useful for finding missing pulses, dropouts, noise, and incorrect CMP-to-CKP timing.
If an expected waveform is absent, first confirm the scope connections and settings, the sensor’s supply and ground where applicable, cranking speed, target rotation, and sensor installation or clearance. Then follow the vehicle-specific test procedure to isolate the sensor from the wiring and target.
If both waveforms look clean individually but synchronization or correlation faults remain, capture them simultaneously. Compare the same reference points under the same engine speed and VVT conditions as a vehicle-specific reference. A clean signal can still be incorrectly timed.
Choosing a Scan Tool for This Check
Start with the data the diagnosis requires. Confirm whether a scan tool supports the target vehicle and can display its Engine RPM, Cam/Crank Sync or cylinder identification status, and desired and actual camshaft angles, where those parameters are available. The ability to graph or record supported data is especially useful for intermittent faults. Full-system coverage by itself does not guarantee access to every enhanced engine parameter.
The THINKSCAN 689BT is a standalone option for full-system scanning, reading supported engine codes, reviewing available live data, and checking for returning faults after a repair. For this diagnosis, its value lies in helping you preserve fault information and observe supported parameters during the conditions that trigger the complaint. Check the exact vehicle and function coverage before relying on a particular sync or VVT parameter. Circuit voltage checks still require a multimeter, while raw CKP and CMP waveform analysis requires compatible automotive oscilloscope hardware and vehicle-specific reference data.
THINKSCAN 689BT
Use supported engine data to compare CKP and CMP diagnostic clues before moving to direct circuit or waveform testing.
- Engine RPM Data
- Enhanced Engine Codes
- Cam/Crank Sync Data
- CMP & VVT Live Data
- Live-Data Graphing
- Recording & Rescanning
Available PIDs and functions depend on the vehicle, engine, control module, and software coverage. Circuit voltage checks still require a multimeter, while raw CKP and CMP waveform analysis requires compatible automotive oscilloscope hardware and vehicle-specific reference data.
Do Crankshaft Camshaft Position Sensors Use the Same Technology?
Not necessarily. Both positions can use passive variable-reluctance sensors or active sensor designs, depending on the engine. When researching crankshaft camshaft position sensors, identify the technology from the vehicle wiring diagram rather than assuming both sensors use the same circuit.
A passive variable-reluctance sensor generates an AC signal as its magnetic field changes. Active designs require an electrical supply and can use different sensing and output methods. Their waveform, voltage, wiring, and test procedure depend on the specific sensor and circuit, not on whether it is called a crankshaft or camshaft sensor.
There is no universal “good resistance” or “correct voltage” that applies to every CKP or CMP sensor. Use the manufacturer’s specification before interpreting a meter reading.
Can You Swap a Crankshaft Sensor With a Camshaft Sensor?
Generally, no. In a camshaft vs crankshaft comparison, the sensors serve different positions in the engine management system, and their fit, connector, signal requirements, and part numbers may differ.
Even if two sensors look alike, appearance is not proof that they are interchangeable. Use the vehicle identification, engine configuration, manufacturer part number, and service information to confirm the correct replacement.
Do you need to replace both at the same time? No routine replacement rule requires it. Test the circuits and identify the cause before buying either sensor. Replacing both together can obscure the original fault and introduces two new parts and installations to check if the problem remains.
What If Both Sensor Signals Look Good?
If CKP and CMP signals are present and stable, continue beyond the sensors. Depending on the code and vehicle, the next checks may include:
- CMP-to-CKP correlation against a vehicle-specific reference
- Timing belt or chain installation and condition
- Trigger-wheel condition and alignment
- Cam phaser position and response
- VVT solenoid operation
- Engine oil level, pressure, condition, and specified viscosity
- Wiring or terminal faults that occur only with heat or vibration
For example, a shifted cam/crank relationship may reflect mechanical timing or VVT operation even though both sensors produce a waveform. VVT and mechanical timing faults can also coexist. Follow the manufacturer’s procedure for establishing the specified VVT reference state before interpreting a correlation measurement.
Frequently Asked Questions
Is a camshaft sensor the same as a crankshaft sensor?
No. The CKP sensor provides a crankshaft position and speed reference. The CMP sensor provides camshaft phase information used for functions such as cylinder identification. The control module interprets both signals according to the engine’s design.
Which sensor is more likely to cause a no-start?
A loss of the CKP signal is often a strong no-start suspect because the module may be unable to determine engine speed and crank position. However, some CMP faults can also cause a no-start on certain engines. Verify RPM, synchronization, codes, and actual signals before choosing a part.
Does a normal cranking RPM reading mean the camshaft sensor works?
No. Engine RPM is generally calculated from crankshaft information. Use a supported CMP or synchronization parameter, then test the CMP circuit or waveform if the result remains unclear.
Can a bad timing chain cause camshaft and crankshaft sensor codes?
Yes. Incorrect mechanical timing can alter the relationship between the signals and set synchronization or correlation faults even when both sensors operate. The exact codes depend on the vehicle and fault.
Is P0340 always a bad camshaft sensor?
No. P0340 directs diagnosis toward CMP circuit operation. Check the connector, wiring, power and ground where applicable, signal, installation, and trigger target before condemning the sensor.
Does replacing either sensor require a relearn?
It depends on the vehicle and repair. Some applications specify a crankshaft position variation learn, cam/crank synchronization procedure, or other calibration after certain repairs; others learn automatically. Check the service procedure for the exact vehicle. Clearing codes is not the same as completing a required learn procedure.
The Practical Difference: Camshaft vs Crankshaft
For a crankshaft vs camshaft position sensor diagnosis, CKP supplies the primary crankshaft angle and speed reference. CMP supplies camshaft phase information that helps the control module identify the engine’s position in the combustion cycle. The module compares the two signals and uses them according to the vehicle’s control strategy.
When either signal is suspected, start with the codes and freeze-frame data. Check cranking RPM and supported synchronization data, inspect the circuits, and test the signals under the conditions that produce the fault. That sequence helps distinguish a failed sensor from wiring, a damaged target, VVT trouble, or incorrect mechanical timing.
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P0340-P0349 Camshaft Position Sensor Codes Explained
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