Camshaft and Crankshaft Sensor Symptoms — How to Tell Which One Is Failing

This article was updated in June 8, 2026 with new products and information by Mark S. Taylor

Your check engine light is on. You scan the codes and see P0340 — camshaft position sensor. Or P0335 — crankshaft position sensor. Or both. Or neither, but the car stalls, misfires, and won’t always start.

These two sensors work as a pair. The engine management system needs both signals simultaneously to run correctly. When either fails — or when both disagree with each other — the symptoms overlap enough to cause real diagnostic confusion. Replacing the wrong one wastes money and leaves the problem unsolved.

This guide explains what each sensor does, what symptoms each produces, how the symptoms differ, how to test both at home, and what the codes are actually telling you — including when the code points to a timing chain problem rather than either sensor.

What Each Sensor Does — And Why the ECU Needs Both

Understanding the function of each sensor is the foundation for everything in this guide.

The Crankshaft Position Sensor (CKP)

The CKP sensor monitors the exact rotational position and speed of the crankshaft by reading a toothed reluctor wheel mounted on the crankshaft. It generates a signal that tells the ECU two things in real time:

• Where each piston is in its stroke at every moment
• How fast the crankshaft is rotating (engine RPM)

The ECU uses this data to calculate both fuel injection timing and ignition timing. It is the primary timing reference — the foundational signal that the entire engine management strategy is built around. Without a CKP signal, the ECU cannot time fuel delivery or spark at all.

The Camshaft Position Sensor (CMP)

The CMP sensor monitors the position of the camshaft — specifically where each camshaft is in its rotation cycle. It reads a tone wheel or reluctor mounted on the camshaft sprocket.

The ECU uses this signal for:

• Cylinder identification — determining which cylinder is approaching TDC on the compression stroke (vs exhaust stroke)
• Sequential fuel injection — injecting fuel in the correct firing order sequence for each cylinder
• Variable valve timing control — on engines with VVT, the CMP signal allows the ECU to monitor and adjust cam timing in real time

Why Both Signals Are Required

Here is the critical insight that explains the symptom differences between the two sensors.

The CKP signal tells the ECU where the pistons are. The CMP signal tells the ECU which cylinders are on the compression stroke vs the exhaust stroke. Without both, the ECU cannot correctly sequence fuel injection — it knows a piston is at the top of its stroke but not whether that cylinder is firing or exhausting.

What happens when the CKP signal is lost: The ECU has no position reference at all. It cannot time fuel injection or ignition. The engine stops immediately or will not start.

What happens when the CMP signal is lost: The ECU loses cylinder identification. On most vehicles it falls back to a non-sequential injection mode — injecting fuel into all cylinders simultaneously rather than in sequence. The engine typically still runs — but less efficiently. Starting may be harder and performance may degrade.

This functional difference explains the most important symptom distinction: A completely failed CKP sensor causes a no-start or immediate stall. A completely failed CMP sensor on most vehicles allows the engine to still run — badly.

Camshaft Position Sensor Symptoms

A failing camshaft position sensor produces symptoms that are often subtler and more varied than CKP failure — particularly on modern engines with variable valve timing.

Rough or Unstable Idle

Without accurate camshaft position data, the ECU’s sequential injection timing becomes imprecise. The engine receives slightly mistimed fuel pulses — causing a rough, irregular idle quality. Unlike the rhythmic miss of a single misfiring cylinder, CMP-related roughness tends to be irregular and variable.

Hard Starting — Especially Cold

On a cold start, the ECU relies on CMP data to correctly sequence the first injection events. A failing CMP sensor forces the ECU into batch injection mode, which is less efficient for cold starts — requiring more cranking attempts before the engine fires. Cold morning hard starts that improve once the engine is warm are a common early CMP failure symptom.

Engine Misfires

An inaccurate CMP signal causes slightly incorrect injection timing for individual cylinders — particularly noticeable at idle and low load. P0300 random misfire codes may appear. These misfires are often misattributed to spark plugs or ignition coils, especially if the misfires are intermittent.

Poor Fuel Economy and Reduced Performance

Batch injection — all injectors firing simultaneously rather than sequentially — is less fuel-efficient than sequential injection. A vehicle running in fallback batch injection mode from a failed CMP sensor uses slightly more fuel and produces slightly less power than normal.

Variable Valve Timing Problems (Modern Engines)

This is where modern CMP sensor failure becomes significantly more complex than older vehicles.

On engines with variable valve timing — virtually all engines manufactured after 2010 — the ECU uses the CMP signal to actively monitor and control cam phasing. The cam actuator (often oil-pressure driven) adjusts the camshaft timing in real time for performance and efficiency.

When the CMP sensor fails on a VVT engine, the ECU loses its ability to monitor actual cam position relative to commanded position. Symptoms include:

• Engine that runs normally at idle but feels significantly underpowered at mid-range RPM where VVT is most active
• Rough running that comes and goes as the ECU attempts VVT adjustments it cannot verify
• Specific VVT-related codes alongside CMP codes — P0011, P0012, P0021, P0022 (cam timing over-advanced or over-retarded)
• Reduced fuel economy as VVT optimization is disabled

Check Engine Light With P0340–P0344 Codes

The ECU logs CMP-specific codes when it detects the sensor signal is absent or outside expected parameters. These codes do not always appear early in the failure process.

Stalling (Less Common Than CKP)

On most vehicles a completely failed CMP sensor does not cause a stall or no-start — the ECU switches to fallback mode and keeps the engine running. However, on some vehicles — particularly those without a fallback injection mode — complete CMP failure does cause a no-start. This varies by manufacturer and model year.

Crankshaft Position Sensor Symptoms

CKP sensor failure tends to produce more dramatic and safety-critical symptoms than CMP sensor failure — because the CKP signal is the primary timing reference that the engine cannot function without.

Engine Stalls While Driving and Restarts After Waiting

The single most distinctive CKP symptom. The engine cuts out suddenly while driving — as if the ignition was switched off. The engine cannot be restarted immediately. After 20–30 minutes of cooling, the car starts and runs normally.

This pattern is caused by heat soak failure — the sensor’s internal components malfunction above a certain temperature and recover when cool. Almost no other single component failure replicates this exact pattern with such consistency.

Engine Cranks But Will Not Start

A completely failed CKP sensor provides no position signal. The ECU cannot time fuel injection or ignition at all. The engine cranks normally at correct speed — the starter is working, the battery is fine — but the engine never fires.

Intermittent Hard Starting

Before complete failure, the CKP sensor may produce a degraded but present signal during some start attempts and no signal during others. Starting becomes unreliable — sometimes first crank, sometimes extended cranking, sometimes no-start. The failure events become more frequent over time.

Random Misfires Across Multiple Cylinders

A degraded CKP signal causes mistimed ignition and fuel injection across all cylinders simultaneously. P0300 random misfire codes appear, sometimes alongside individual cylinder codes. These misfires are commonly misdiagnosed as spark plug or ignition coil failure.

Engine Hesitation Under Hard Acceleration

The CKP signal frequency increases with RPM. A sensor that produces adequate signal at low RPM may fail at higher frequencies encountered during hard acceleration — causing a stumble that closely resembles a fuel delivery or ignition coil fault.

Reduced Fuel Economy

Timing variations from a degraded CKP signal cause combustion inefficiency across all cylinders — wasting fuel. Often one of the earlier subtle signs before dramatic symptoms develop.

For a complete treatment of all CKP sensor symptoms and the heat soak failure pattern, see our detailed guide on crankshaft position sensor symptoms.

Side-by-Side Comparison — Cam vs Crank Sensor Symptoms

Symptom	CMP Sensor (Cam)	CKP Sensor (Crank)
Complete no-start	Uncommon — most vehicles have fallback mode	Very common — no signal = no start
Stalls while driving	Uncommon	Very common — especially heat soak pattern
Stalls and restarts after 20–30 min	Rare	Classic CKP heat soak pattern
Hard cold start	Common	Common
Hard hot start	Less common	Very common — heat soak
Rough idle	Common	Common
Random misfires	Common	Common
Hesitation under acceleration	Moderate	Strong
VVT-related issues	Yes — on modern engines	Not directly
Poor fuel economy	Yes	Yes
Check engine codes	P0340–P0344	P0335–P0339
Severity of failure	Moderate — engine usually still runs	Severe — engine often cannot run
Symptom onset	Often gradual	Can be sudden
Heat sensitivity	Less common	Very common

OBD Codes — Cam vs Crank

Crankshaft Position Sensor Codes

Code	Meaning
P0335	CKP sensor A circuit malfunction
P0336	CKP sensor A circuit range/performance
P0337	CKP sensor A circuit low input
P0338	CKP sensor A circuit high input
P0339	CKP sensor A circuit intermittent

Camshaft Position Sensor Codes

Code	Meaning
P0340	CMP sensor A circuit malfunction — Bank 1
P0341	CMP sensor A circuit range/performance — Bank 1
P0342	CMP sensor A circuit low input — Bank 1
P0343	CMP sensor A circuit high input — Bank 1
P0344	CMP sensor A circuit intermittent — Bank 1
P0345	CMP sensor A circuit malfunction — Bank 2
P0365	CMP sensor B circuit malfunction — Bank 1

Variable Valve Timing Codes (When CMP Fails on VVT Engine)

Code	Meaning
P0011	Cam timing over-advanced Bank 1
P0012	Cam timing over-retarded Bank 1
P0021	Cam timing over-advanced Bank 2
P0022	Cam timing over-retarded Bank 2

The Correlation Code

Code	Meaning
P0016	Crankshaft-camshaft position correlation — Bank 1 Intake
P0017	Crankshaft-camshaft position correlation — Bank 1 Exhaust
P0018	Crankshaft-camshaft position correlation — Bank 2 Intake
P0019	Crankshaft-camshaft position correlation — Bank 2 Exhaust

P0016 — When It’s Not the Sensors at All

This is the most important section in this guide for drivers who have been told both sensors need replacing.

P0016 — and its siblings P0017, P0018, P0019 — are correlation codes. They mean the ECU is receiving signals from both the cam sensor AND the crank sensor, but the two signals are not in the relationship they should be. The cam position and crank position don’t agree with each other.

What causes a correlation code:

The relationship between cam and crank position is fixed by the timing chain or belt. If a P0016 appears with both sensors testing electrically sound — the sensors are actually doing their jobs correctly. They’re accurately reporting positions that are genuinely out of sync. The timing chain is the cause.

Timing chain stretch: As a timing chain wears over miles, it stretches and sags. This allows the camshaft to slip slightly behind its correct timing relationship with the crankshaft. The CMP signal shows the cam is slightly retarded relative to what the CKP signal reports it should be. P0016 appears.

What happens if P0016 is misdiagnosed as a sensor problem: A mechanic or driver replaces both the cam sensor and the crank sensor. Both sensors test perfectly electrically. Both sensors are replaced. P0016 returns immediately — because the sensors were never the problem. The timing chain is stretched and needs replacement.

How to distinguish timing chain stretch from sensor failure:

• P0016 with both sensors reading electrically normal = timing chain problem
• P0016 with one or both sensors reading out of specification = sensor may be at fault
• P0016 that is accompanied by a rattling sound from the engine on startup = timing chain rattle — strong confirmation
• P0016 on a vehicle with over 100,000–150,000 miles without a timing chain service = high probability of chain stretch

The consequence of missing this: A stretched timing chain is a significant repair — $800–$2,500 on most vehicles. But driving with significant timing chain stretch risks catastrophic engine damage if the chain jumps a tooth or breaks. A P0016 that points to chain stretch should not be dismissed or patched with sensor replacement.

Is It the Cam, the Crank, or Both? — Diagnostic Decision Guide

Use this decision guide before replacing anything.

Observation	Most Likely Cause	First Step
Engine cranks normally, won’t start at all	CKP sensor	Check CKP live data during cranking
Engine starts but runs very rough, eventually starts after cranking	CMP sensor	Check CMP code and live data
Engine stalls while driving, restarts after 20–30 min	CKP heat soak	Hot restart test, CKP replacement
Engine stalls while driving, restarts immediately	Could be either — or fuel	Scan for codes first
Rough idle, hard cold start, fuel economy down	CMP sensor likely	Check CMP codes, VVT codes
P0335 code only	CKP sensor	Test CKP circuit
P0340 code only	CMP sensor	Test CMP circuit
P0335 AND P0340 both present	Could be wiring, could be both sensors	Check common ground and wiring first
P0016 present, sensors test electrically normal	Timing chain stretch	Do not replace sensors — inspect chain
P0016 AND P0011/P0012 present	VVT and timing issue	Timing chain inspection priority
VVT performance symptoms, no misfire codes	CMP sensor on VVT system	Check CMP and VVT actuator

How to Test Both Sensors at Home

Step 1 — Scan for all codes

Pull every code present — not just the active ones. Pending codes and stored codes matter. Note whether codes are CKP-specific, CMP-specific, correlation codes, or VVT codes. This map guides the entire diagnosis.

Step 2 — Check live data during cranking

Connect a scan tool with live data capability. Monitor both the CKP RPM signal and the CMP signal simultaneously during a cranking event:

• CKP should show RPM rising and falling with the starter
• CMP should show a signal pattern synchronized with the CKP signal
• A completely absent CKP reading during normal cranking = CKP sensor or wiring failure
• A present CKP signal with absent or erratic CMP signal = CMP sensor or wiring

Step 3 — Resistance test — CKP sensor

Disconnect the CKP connector. Set multimeter to ohms. Test between signal terminals:

• Magnetic pickup type: 500–1,500 ohms — zero or infinite = failed
• Hall effect type: test for supply voltage (5V or 12V) at power terminal instead

Step 4 — Resistance test — CMP sensor

Disconnect the CMP connector. Set multimeter to ohms. Test between signal terminals:

• Magnetic pickup type: 200–900 ohms — varies by manufacturer, confirm with service data
• Hall effect type: check supply voltage at power terminal; signal output should toggle between low voltage and supply voltage as engine cranks

Step 5 — Wiring harness flex test — both sensors

With each connector disconnected and the multimeter monitoring resistance, flex and move each wiring harness along its full length. Any change in resistance reading during movement indicates a broken wire inside the insulation — causing symptoms identical to sensor failure. This test is critical for CKP sensors, which are mounted in the hottest area of the engine bay and have harnesses subject to heat cycling.

Step 6 — The hot restart test (CKP specific)

After a full warm-up drive, turn the engine off and immediately attempt a restart. If the engine won’t start hot but starts fine after 20–30 minutes of cooling — CKP heat soak is confirmed. If the engine restarts immediately after being switched off hot — CKP heat soak is not the issue for that symptom.

Step 7 — Monitor simultaneous live data during a drive

The most comprehensive home test: drive with a Bluetooth OBD adapter and live data app active. During any symptom event — rough running, hesitation, stumble — review what the CKP and CMP channels showed at the exact moment of the event. A dropout in the CKP channel during a stumble is definitive. A CMP channel anomaly during a VVT symptom event pinpoints that sensor.

Should You Replace Both Sensors at the Same Time?

This is a legitimate practical question — and the answer depends on the situation.

Cases where replacing both makes sense:

• Both P0335 and P0340 are present and both sensors test at the edge of specification
• The vehicle has over 150,000 miles and neither sensor has been replaced
• One sensor has been confirmed failed and the other shows borderline resistance
• The labor to access one sensor also requires removing the other — the additional parts cost is minimal compared to returning to the shop for the second replacement

Cases where replacing both is unnecessary:

• Only one sensor has a confirmed fault and the other tests within specification
• P0016 is present — replacing sensors won’t fix the correlation code if the timing chain is stretched
• The failed sensor was clearly caused by a specific event (wiring damage, oil contamination) that doesn’t apply to the other sensor

Cost consideration: Sensors themselves are relatively inexpensive — $20–$100 each for most vehicles. If replacing both sensors requires the same labor access, the incremental cost of adding the second sensor is often less than $50 in additional parts. In that scenario, replacing both simultaneously is reasonable insurance.

Is It Safe to Drive With Either Sensor Failing?

Symptom	Safe to Drive?	Action
CMP code only, engine runs normally	Yes, short term	Diagnose within a week
Rough idle from CMP failure	Caution	Diagnose within a few days
VVT symptoms from CMP failure	Yes, short term	Diagnose within 2 weeks
CKP code only, starts reliably	Caution — progressive	Replace within a week
CKP intermittent hard start	No — will worsen	Fix promptly
CKP stall event occurred	No — safety risk	Fix before next significant drive
P0016 with timing chain symptoms	No — chain damage risk	Diagnose immediately
Both sensors failing	No	Fix immediately
Engine cranks but won’t start	No	Tow to shop

Repair Cost Summary

Service	DIY Friendly?	Average Cost
OBD scan (both sensors)	Yes	$0–$25
CKP sensor replacement — parts	Yes — intermediate	$20–$100
CKP sensor replacement — shop	N/A	$150–$350
CMP sensor replacement — parts	Yes — intermediate	$20–$80
CMP sensor replacement — shop	N/A	$100–$300
Both sensors replaced — shop	N/A	$200–$550
CKP relearn procedure	Mechanic sometimes	$0–$100
CMP/VVT relearn procedure	Mechanic sometimes	$0–$100
Wiring harness repair	Mechanic recommended	$100–$350
Timing chain replacement (P0016)	Mechanic only	$800–$2,500

FAQs About Camshaft and Crankshaft Sensor Symptoms

What is the difference between camshaft and crankshaft position sensor symptoms?

The key difference is severity. A completely failed crankshaft position sensor causes the engine to stop running entirely or prevents starting — the CKP signal is required for both fuel injection and ignition timing. A completely failed camshaft position sensor on most vehicles allows the engine to still run because the ECU falls back to batch injection mode. CKP failure tends to be more dramatic and safety-critical. CMP failure tends to produce subtler symptoms like rough idle, hard cold starting, and VVT issues.

Can a bad camshaft sensor cause a no-start?

On most modern vehicles with fallback injection modes, a completely failed CMP sensor does not prevent starting — the ECU switches to batch injection. However, on some vehicles without a fallback mode, particularly some European and older vehicles, complete CMP failure can cause a no-start. When a no-start occurs with a P0340 code present, testing whether the vehicle has a fallback mode is an important diagnostic step.

What does the P0016 code mean?

P0016 is a cam-crank correlation code — it means the ECU is receiving signals from both sensors but the cam position and crank position are not in the correct relationship. On most vehicles the cause is timing chain stretch rather than sensor failure. If both sensors test electrically normal but P0016 is present, do not replace the sensors — have the timing chain inspected.

How do I know if it’s the cam or crank sensor causing my stalling?

The 20–30 minute restart window is the most distinctive diagnostic clue. If the engine stalls while driving and restarts normally after 20–30 minutes of cooling, the crankshaft position sensor heat soak is the cause. If the engine stalls but restarts immediately or within seconds, the CMP sensor or another cause is more likely. Scanning live data during a stall event to check which sensor’s signal dropped out provides the definitive answer.

Should I replace both cam and crank sensors at the same time?

If both sensors are original on a high-mileage vehicle, if both show borderline resistance readings, or if the labor to access one requires access to the other anyway — replacing both simultaneously is reasonable. If only one sensor has confirmed fault and the other tests within specification, replacing both is not necessary. Never replace both sensors when P0016 is the primary code — that code points to the timing chain, not the sensors.

How much does it cost to replace cam and crank sensors?

Individual sensor replacement typically costs $100–$350 at a shop depending on the vehicle and sensor accessibility. Replacing both sensors at the same visit typically costs $200–$550. The sensors themselves cost $20–$100 each — the majority of the cost is labor, which varies significantly based on how accessible each sensor is on the specific vehicle.

The Bottom Line

Camshaft and crankshaft sensors work as a team — the ECU needs both to run the engine correctly. When either fails, the symptoms overlap enough to create diagnostic confusion. The key to avoiding expensive misdiagnosis is understanding what each sensor is actually responsible for.

The CKP sensor is more critical — it’s the primary timing reference, and its failure tends to be more dramatic. The CMP sensor failure tends to be subtler — the engine usually still runs, just not as well. And when you see P0016, stop before replacing either sensor and investigate the timing chain first.

Quick Summary:

• CKP failure = dramatic symptoms — complete no-start, stall while driving, heat soak pattern
• CMP failure = subtler symptoms — rough idle, hard cold start, poor fuel economy, VVT issues
• The 20–30 minute stall-and-restart pattern = CKP heat soak, almost definitively
• P0016 correlation code usually points to timing chain stretch — not sensor failure
• VVT-related codes alongside CMP codes indicate modern engine VVT system issues
• Live data monitoring during a symptom event provides the most definitive diagnosis
• Both codes present simultaneously — check the wiring and common grounds before replacing both sensors
• Always check whether the specific vehicle has a CMP fallback mode before concluding a no-start is CMP-related