Cam and crank sensor failure: signs and costs

August 20, 2026The drivway Team

There's a specific kind of car problem that makes people doubt themselves. The car stalls at a red light, restarts on the third try, and drives home perfectly. You take it to a shop, they can't reproduce it, and you leave with an invoice for a diagnostic and no repair. Two weeks later it strands you in a parking lot on a hot afternoon.

That pattern — intermittent, heat-related, no obvious cause — points more often than not at one of two small sensors: the crankshaft position sensor or the camshaft position sensor. The parts are cheap. The diagnosis is where the money is, and where a good shop earns it.

What these two sensors actually do

Modern engines don't guess. The engine computer needs to know exactly where the crankshaft and camshafts are, degree by degree, to decide when to fire each spark plug and each fuel injector.

The crankshaft position sensor (CKP) reads a toothed ring on the crankshaft. It's the primary timing reference — the signal the computer uses to know engine speed and piston position. Lose it completely and the engine won't run at all.
The camshaft position sensor (CMP) reads the camshaft, telling the computer which cylinder is on its compression stroke and, on engines with variable valve timing, whether the cams are where they were commanded to be. Lose it and many engines will still start and run, just badly.

That difference is why the symptoms differ, and it's the first thing to sort out.

The symptoms, and which sensor they point to

Crankshaft sensor (CKP) — the stalling and no-start one:

The engine dies without warning, often at idle or as you lift off the throttle, and restarts after a wait.
Cranks but won't start, especially after the engine is hot — then starts fine once it cools down. This "heat soak" pattern is the single most recognizable crank-sensor symptom, and it's why the problem so often refuses to appear at the shop on a cold morning.
The tachometer drops to zero or goes erratic while cranking or driving. That's a strong tell, because the tach reads straight off this sensor on most cars.
A check engine light with P0335 (crankshaft position sensor "A" circuit malfunction) or a related P0336/P0339.

Camshaft sensor (CMP) — the runs-badly one:

Long cranking before it fires, then it runs.
Rough idle, misfires, hesitation on acceleration, sometimes a noticeable loss of power or reduced fuel economy.
Occasionally a car that won't shift normally — some transmissions use engine data the computer can't produce cleanly without a good cam signal.
A check engine light with P0340, P0341, or a cylinder-specific variant.

Should you keep driving it?

Treat an active crank-sensor fault as a stop-driving problem. An engine that shuts off at highway speed takes power steering and brake assist with it — the brakes and steering still work, but they get heavy and unfamiliar at exactly the wrong moment. If your car has stalled unexpectedly in traffic, get it diagnosed before your next long drive rather than after it.

A cam sensor fault that shows up as a rough idle is less urgent, but it isn't nothing: a persistent misfire dumps unburned fuel into the exhaust, and that's how a $200 problem turns into a $1,500 catalytic converter.

The trap: the cheap part that hides an expensive cause

Here's the part worth knowing before you approve anything. These codes name a circuit, not a part. P0340 means the computer didn't get a valid cam signal — it does not mean the sensor is bad. The same code is regularly caused by:

A damaged wiring harness or corroded connector. These sensors live in hot, dirty places, often against the back of the engine or low near the crank pulley. Heat-hardened insulation, chafed wires, oil-soaked connectors, and rodent damage all produce identical codes.
Oil contamination on the sensor tip, usually from a leaking cam seal or valve cover gasket. Replacing the sensor fixes it for a few months, then the new one fails the same way. The leak is the actual repair.
A damaged reluctor or tone ring — the toothed wheel the sensor reads. A chipped tooth reads as a missing signal.
A stretched timing chain. This is the expensive one. A worn chain lets cam timing drift relative to the crank, so the computer sees a cam signal that's real but wrong, and logs a cam code — very often alongside P0016 (crank/cam correlation). A shop that replaces the sensor here has fixed nothing, and the chain keeps wearing.

So ask one question before the work starts: "Did you confirm the sensor itself is bad, or just read the code?" A real answer sounds like "we scoped the sensor signal, checked the reference voltage and ground at the connector, and compared cam-to-crank correlation on the scan tool." An answer that's only "it's got a P0340" is a parts guess with your money.

If you see P0016 or any correlation code sitting next to the cam code, say so out loud and ask specifically whether timing chain stretch has been ruled out. That one question is worth more than everything else in this article.

What should this cost?

Diagnosis first. Expect $100–200 at an independent shop for a proper diagnosis, and more if the fault is intermittent and they need to road-test with a scan tool recording. Many shops credit it toward the repair. On a symptom this intermittent, paying for real diagnosis is almost always cheaper than paying for parts twice.

If it is just the sensor:

Crankshaft position sensor, independent shop: commonly $150–400 all-in on a typical four-cylinder or V6 where the sensor is reachable. The part itself is usually $40–150.
Camshaft position sensor, independent shop: commonly $150–350, and many engines carry two or four of them — replacing one is the norm, not the set.
Dealership: generally 20–35% higher for the same job, mostly a labor-rate difference (independents typically bill $90–150/hr against a dealer's $150–250+) plus OEM-only parts pricing. On a luxury brand the gap can approach double.
Awkward-access engines run higher. A sensor buried under the intake manifold, behind the timing cover, or at the back of a transverse V6 can turn a 20-minute job into three hours, and $500–800 is realistic when major components have to come off first.

If it's one of the other causes:

Repairing a chafed wire or corroded connector: often $100–300, and it's the outcome you want.
Fixing the oil leak contaminating the sensor: varies widely — a valve cover gasket is commonly $150–450; a cam seal more.
Timing chain replacement: this is the four-figure branch, commonly $1,000–2,500+ depending on engine, and considerably more on engines where the chain is at the transmission end.

One note on parts: position sensors are a component where cheap really is cheap. Bargain-bin sensors have a well-earned reputation for failing within a year or reading inaccurately from new. Ask what brand the shop is fitting — an OE-quality part from a known supplier is worth the small difference on a job whose labor you don't want to pay twice.

Independent shop or dealer?

This is a good independent job, with one qualifier: pick the shop for its diagnostic ability rather than its hourly rate. The part is inexpensive everywhere and the labor is usually modest, so essentially all of your risk sits in whether someone correctly identifies which of the five causes above you actually have. A technician who talks about scoping the signal, checking correlation data, and inspecting the connector before ordering a part will save you more than a lower labor rate ever will.

And if a shop has already replaced the sensor once and the code came back, don't buy a second sensor. Something upstream — wiring, oil, tone ring, or timing — is still there.

Stalling, hard to start when hot, or staring at a P0335? Find a local technician who can diagnose it properly on drivway.