Camshaft Position Sensor

The crankshaft sensor tells the computer the crank angle, but a four-stroke engine takes two crank revolutions per cycle, so crank angle alone cannot tell compression stroke from exhaust stroke. The camshaft turns once for every two crank turns. Comparing the two signals tells the computer exactly which cylinder is where in its cycle, so it can fire the correct coil and the correct injector at the correct instant. On an engine with variable valve timing, the same sensor reports where the camshaft actually is relative to the crank, so the computer can control the phaser and confirm it moved. One consequence matters before any of the diagnosis does. On engines that cannot run on the crank signal alone, a cam signal that drops out shuts the engine off — sometimes while you are driving. If that happens, the steering and brakes still work mechanically, but both get much heavier: power assist is gone as soon as the engine stops, and on many vehicles with electric power steering the assist cuts out too, while vacuum brake boost is usually good for only a pedal application or two. Keep both hands on the wheel, do not turn a mechanical key to OFF or LOCK and do not hold the stop button on a push-button car while moving, because the column can lock. Signal, coast to the shoulder, brake with one firm steady push rather than pumping, then restart or call for a tow. A vehicle that has stalled once at speed should not be driven in traffic, on a highway, or with passengers until the fault is found — an intermittent sensor gives no warning about when it will do it again.

The sensor faces a target on the camshaft, the cam gear, or the phaser — teeth, lobes, or a slotted ring. Two technologies are used. A variable reluctance sensor is a magnet wound with a coil, two wires, generating its own alternating voltage as teeth pass; its output grows with speed, so it can produce a weak signal at cranking speed if the air gap is wrong. A Hall-effect sensor has three wires — power, ground, and signal — and produces a clean square wave at any speed, including very slow cranking, which is why nearly all modern applications use it. The computer compares cam signal edges against the crank signal and checks that the relationship falls within an expected window. Variable valve timing closes another loop: the computer commands an oil control valve, engine oil pressure rotates the phaser on the end of the camshaft, and the cam sensor reports back how far it actually moved. That entire loop depends on adequate, clean oil at the right pressure. This is the single most important thing to understand about this part: a cam-to-crank correlation code says the two signals are not in the relationship the computer expects. That is a detection, not a verdict. The sensor is the instrument reading the relationship, not usually the thing that broke it.

Internal electronics degrading with heat, giving the classic pattern of working cold and dropping out once hot — an intermittent stall or a crank-no-start that fixes itself after an hour. A cracked housing or a hardened O-ring letting oil into the sensor. Oil wicking up through the wiring from a leaking seal, corroding the connector and sometimes reaching the computer's connector. Connector corrosion, spread terminals, and harness chafe, which are frequently the real fault. A contaminated or damaged target — metal debris stuck to the magnet, a cracked reluctor ring, a cam gear that has slipped. An incorrect air gap after a careless installation. And the impostors, which on correlation codes are more likely than the sensor itself: a stretched timing chain, worn chain guides, a weak or failing chain tensioner, a chain that has jumped a tooth, a VVT phaser stuck or worn, a clogged screen in the oil control valve, low oil level, low oil pressure, or oil that is overdue and too thick with sludge to move the phaser. Low or dirty oil sets cam timing codes routinely, and replacing the sensor will not touch that.

Mounted in the cylinder head or the timing cover, facing the end of a camshaft or the cam phaser. An engine may have one, two, or four of them. Which one the computer calls bank 1 versus bank 2, and sensor A versus sensor B, is vehicle-specific — bank 1 is the bank containing cylinder number 1, and on many V engines that is not the side you would guess. Look it up before removing anything, because replacing the wrong sensor is a common and avoidable mistake.

Typically $120–$450 at a US independent shop.

US independent shop, parts and labor, for an accessible sensor. The sensor itself is often inexpensive; buried sensors under an intake manifold or behind a timing cover raise labor considerably. If the diagnosis turns out to be a timing chain, phaser, or tensioner, the repair is in a completely different cost bracket — often four figures — which is exactly why the diagnosis has to come before the parts.

Ranges are wide because access varies enormously between vehicles — the same part can be a twenty-minute job on one engine and a half-day on another.