You're driving along normally, the engine suddenly cuts out mid-drive, you turn the key and nothing. You wait ten minutes or so, the engine fires up like nothing happened. Next day, same story. The most common culprit for this kind of behaviour is the crankshaft position sensor (CKP) and the camshaft position sensor (CMP), two small parts the engine computer (ECU) cannot manage without.
What the crankshaft and camshaft sensors actually do
The crankshaft sensor tells the engine computer where the crankshaft is in its rotation and how fast it's spinning. Without that signal, the ECU cannot work out ignition and fuel injection timing. In other words, the engine has no idea when to fire a spark or inject fuel, so it stalls or refuses to start at all.
The camshaft sensor is a reference sensor. It tells the computer which stroke the engine is on, whether a given cylinder is in intake, compression, power or exhaust. On modern engines with variable valve timing (VVT, VANOS, VVT-i) the camshaft sensor matters even more, because the ECU uses it to control the camshaft position itself.
The two sensors work as a pair. The ECU constantly compares their signals, and if the correlation is off, you get a P0016 or P0017 fault code. That's why you have to think of them as a pair, not as two unrelated parts.
Classic crankshaft sensor failure symptoms
The most recognisable symptom is heat-related failure. The car drives perfectly while the engine is cold, and once it reaches operating temperature, it randomly stalls. Trying to restart right away gets you nowhere, the starter cranks the engine but it won't catch. After 10-20 minutes of cooling down, the sensor "recovers" and the engine fires up normally. The next day the same thing happens.
The second typical symptom is unstable idle. The engine "hunts", the tachometer needle jumps around, and you sometimes feel a loss of power under acceleration. Early on the check engine light may stay off, because the ECU sees an intermittent signal and doesn't log a permanent fault.
The third symptom is hard hot starting. Cold, the engine fires on the first crank; warm, it needs two or three cranks before it catches. A lot of drivers blame the battery or the starter, when the real culprit is a crankshaft sensor giving a weak signal once it heats up.
When the camshaft sensor fails and how it differs
The camshaft sensor leaves drivers stranded less often, but it causes a different kind of trouble. The classic giveaway is a longer time before first ignition. You turn the key, the engine cranks three or four seconds longer than usual, and then finally fires. In that moment the ECU is running without a camshaft signal and falling back on a backup strategy, trying to guess the stroke.
While driving you'll notice a mild loss of power, rough running and worse fuel economy. On engines with variable valve timing you may feel jerks when transitioning between low and mid revs. The engine usually doesn't stall, but it doesn't feel healthy either.
A very common cause of camshaft sensor failure is oil leaking from the valve cover gasket. Oil soaks the sensor connector, creates short circuits, and the sensor starts sending bad signals. If you change the sensor without replacing the gasket, the new sensor will meet the same fate within a few months.
Why the fault only shows up once the engine is warm
This is the diagnostic key that separates the crankshaft sensor from other faults. Inside the sensor there's a fine wire winding that generates voltage. When the engine warms up, heat expands the materials and a microscopic break in the winding gets wider. A cold winding works, a hot winding breaks the connection and the signal disappears.
That's how a sensor fault differs from a fuel pump fault. A pump fails under load, on hills or under acceleration; while the car is sitting at idle the pump still puts out enough pressure. The crankshaft sensor is the opposite, it fails thermally regardless of load, most often in stop-and-go traffic when the engine is sitting at operating temperature.
This distinction matters because a mechanic who skips this step can start swapping pumps, fuel filters and spark plugs before checking the sensor. An hour on the diagnostic tool saves you a couple of hundred KM in pointless work.
How it shows on a diagnostic tool and what to check before replacing
On an OBD scanner the typical codes are P0335 and P0336 for the crankshaft sensor, P0340 and P0341 for the camshaft sensor, plus P0016 and P0017 indicating a correlation issue between the two. Better diagnostic tools also let you watch the signal in real time, so you can see exactly when it drops out.
Before swapping the sensor, two things absolutely have to be checked. The first is the toothed reluctor ring on the flywheel or crankshaft pulley. If the ring is broken, bent or has lost a tooth, a new sensor won't fix the problem. The second is the state of the connector and wiring. Oil contamination, oxidised pins and a pinched cable produce the same symptoms as a bad sensor.
In our shop in Banja Luka we usually pin this fault down on the OBD, but we always start by checking whether the CMP sensor is sitting in oil and whether the CKP reluctor ring is sound. Replacing the sensor without that check is throwing money away. As for the part itself, an OEM-grade sensor (Bosch, VDO, Hella) lasts for years, while cheap unbranded sensors often fail the same way after 10-20,000 km.
Can you keep driving with the warning light on, and when to stop immediately
The short answer is no. Technically you can drive as long as the engine starts, but it's risky for two reasons. First is safety: if the engine has already cut out once while driving, next time it could die in a corner, on a railway crossing or while overtaking. Second, with a faulty CKP or CMP signal the timing can drift and you can end up with detonation, and on some engines, piston-to-valve contact.
The rule is simple. If the engine has stalled on its own once while driving, end the trip as soon as you reach somewhere safe and book a diagnostic check. If you see the check engine light without the engine cutting out, drive the car home and don't put off having it looked at. This isn't an expensive repair when it's done right, but it can turn expensive if you drive it into something worse.
If you're not sure what's going on with the car, stop by the shop and we'll do an OBD check on the spot. Better to check now than end up stuck on the side of the road.