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