Crankshaft position sensor

the crankshaft position sensor wiring. For example, in some Ford and Mazda vehicles, if the sensor wires are not secured properly, they could rub against a drive shaft, which can cause intermittent stalling.

How the crankshaft position sensor is tested

Whenever there is a suspicion that the problem might be caused by a crankshaft position sensor or if there is a related trouble code, the sensor must be visually inspected for cracks, loose connector pins or other obvious damage. The proper gap between the tip of the sensor and the reluctor wheel is also very important.

The correct testing procedure can be found in the service manual. We posted several links where you can access a service manual for a subscription fee at the bottom of this article.

For the pick-up coil type sensors, the testing procedure includes checking the resistance.

Crankshaft position sensor
The resistance of this crankshaft position sensor from
the 2008 Ford Escape measures at 285.6 ohms,
which is within specifications

For example, for the 2008 Ford Escape, the resistance of the crankshaft position sensor (CKP) should be between 250-1,000 ohms, according to Autozone. We measured 285.6 ohms (in the photo) which is within specifications. If the resistance is lower or higher than specified, the sensor must be replaced.

For the Hall-type sensors, the reference voltage (typically +5V) and the ground signal must be tested. The most accurate way to test a crankshaft position sensor is checking the sensor signal with an oscilloscope.

Sometimes, the sensor may have an intermittent fault that is not present during testing. In this case checking for Technical Service Bulletins (TSBs) and researching common problems may help.

For example, the crankshaft position sensor failure was very common in some early-90's GM cars. One of the symptoms was stalling when the engine is hot. According to many owners at various forums, the new crankshaft position sensor solved the problem.

Engine RPM graph
Signal from the crankshaft position sensor is
represented as "Engine RPM" in an OBDII scan tool.

The crankshaft position sensor can be checked with a scan tool, that shows it as "Engine RPM" or "Engine speed." For example, if the sensor causes intermittent stalling, you might be able to see that when the engine stalls, the RPM signal drops suddenly to zero, as oppose to slowing down gradually.

If the RPM signal suddenly drops to zero means that the signal from the crankshaft position sensor is lost. If the sensor works properly, the RPM signal should drop or rise gradually, as in this photo. We have tested this car with an OBDII "Torque" app on the mobile phone.

Crankshaft sensor replacement

Replacing a crankshaft position sensor is not very expensive. The part can cost from $35 to $115 and it's best to use an OEM part. In most cars it's fairly easy to replace, although sometimes the sensor could be difficult to remove due to corrosion.

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