How a Crankshaft Angle Sensor Works
Crankshaft Position Sensor (CKP) - Computer controlled vehicles us ea vast array of sensors to keep track of what the engine is doing, among the most important is the crankshaft position sensor. This sensor goes by a few different names depending on the manufacturer, crankshaft angle sensor, CKP sensor, crankshaft position sensor. Regardless of what is called, the function is the same, to accurately tell the PCM (powertrain control module) the position of the crankshaft for ignition timing and injector pulse. In this article we will explain what this very important piece of electronics does, and why it is necessary to make your vehicle perform at its optimum. Crankshaft position sensors have been around for many years, with the advent of fuel injection and computer controls it became necessary to keep tabs on the position of the crankshaft while the engine is running so the computer knows when spark should be applied, when a misfire is occurring and when the injectors should be fired. Injector firing is information that is compiled from the crankshaft position sensor and the camshaft position sensor as a set, the PCM notes the correlation and position of the two and fires the injectors from that information. Spark is controlled from information gathered by the crankshaft position sensor, which is basically the ignition timing. The PCM can advance the timing or retard it depending on what it sees the crankshaft doing through the crankshaft position sensor and feedback from the knock sensor (detonation-pinging) if so equipped. A crankshaft position sensor uses a simple magnetic coil and reluctor (toothed or slotted) wheels to determine the position of the crankshaft. The number of teeth or slots on the wheel depends on the number of cylinders in the engine, for instance a V-8 Ford wheel may have 36 teeth with 1 wide spaced slot, and a V-10 might only have 40 teeth plus the wide slot, depending on how the system is engineered. A wide slot or gap is used on the reluctor wheel so the PCM has a reference point on the crankshaft, it can then determine when the next cylinder needs spark by the amount of times the sensor is triggered after the wide gap in the teeth or slots. This gap is very important to the PCM, it also uses the amount of time it takes for the crankshaft to return to the gap to determine an engine misfire. When this happens, the PCM then uses known parameters to determine which cylinder is the misfire by seeing exactly when the crankshaft slows down in the firing order. When spark is applied the crankshaft should temporarily speed up, when that isn’t seen by the crankshaft position sensor, the computer knows that there is something wrong with that cylinder. Detonation can do the same thing, but for that the PCM would see information from the knock sensor that it is picking up detonation (pinging) and would then retard ignition timing to compensate.
Location of the crank angle sensor varies by manufacturer; some are in the front of the engine, some rear and a few in the center, so consult a repair manual for the exact location of the sensor in your vehicle. When a crankshaft position sensor fails, the vehicle usually wont start. The PCM has to see crankshaft rotation before it will turn on specific items, besides the fact that it doesn’t know when to apply spark due to no rotation of the crankshaft. These failures will usually set a trouble code in the PCM, referring to signal of the crankshaft position sensors, or lack thereof. If your crankshaft position sensor needs replacing, always use an OEM (Original Equipment Manufacturer) part or equivalent. A cheaper sensor may not last as long or perform as well. Replacement of the crankshaft angle sensor is usually fairly easy, depending on location. Before tackling this job, refer to a service manual for location, and then look to see if any special tools would be required to remove and reinstall it. Sometimes ¼ inch drive universal sockets are needed to remove the retaining bolts, as they aren’t always in an easily accessible spot. If further assistance is needed, our certified car repair technicians are ready to answer your car questions. Related Car Repair Information